J2EE Interview Questions and Answers for 2023 Programming

• Increases Development Productivity: J2EE offers a component-based approach for the development of an application. Well-designed generic components may be reused and mapped to the desired function of the application and service to be produced, as this method can increase development productivity.  
• Support for upcoming Web Service Levels: The WS-I Basic Profile and web services are both fully supported by the J2EE 1.4 platform. This makes it possible to easily expose apps as web services. More importantly, this guarantees that web services created on the J2EE 1.4 platform are interchangeable with web services created on any platform that complies with WS-I standards as well as transferable between J2EE implementations.  
• Provides Industry-standard Interfaces: Interfaces for interacting with enterprise information systems (EIS) like the JDBC API, JMS, and J2EE Connector Architecture can be accessed with the J2EE 1.4.  

Additionally, J2EE 1.4 is the ideal foundation for integrating current EIS by exposing their data to users running on multiple interfaces thanks to the additional support for web services.  

• Scalable to accommodate changing demand: J2EE containers offer tools for scalable life cycle management, database connectivity, transaction support, and scaling without coding from application developers.  
• Offers a Customizable Security Framework: Flexibility is a key component of the security model. It makes it simple for application developers to specify the method-level security requirements for components. Specific data operations would only be accessible to users with the necessary permissions.  
• Modularity: When a fully functional server-side application is created, the resulting code is vast and complex. This vast and sophisticated application can be divided into several modules, each of which is in charge of carrying out a distinct duty. The program will be significantly simpler to maintain and comprehend as a result. 

• The Java IDL/CORBA: Developers can combine Java with CORBA with Java IDL support. They can produce Java classes that act as clients for CORBA objects that are expanded with more orbs, or they can produce Java objects and make them available in CORBA orbs. The first strategy offers an additional method for integrating a new application with the existing system using Java.  
• JDBC (Java Database Connectivity): The JDBC data access API offers a consistent method to access various databases. JDBC hides developers from some of the complexities, similar to ODBC. Additionally, JDBC access to databases is cross-platform.  
• JTA (Java Transaction Architecture): Applications can access various transaction monitoring through the standard API defined by JTA.  
• JMS (Java Message Service): The JMS is used for interacting with message-oriented middleware. It enables accredited messaging, transactional messaging, consistent messaging, and permanent subscriber support. It also supports point-to-point and public/subscribe domains. JMS offers an additional method for integrating your application with old backend systems.  
• RMI (Remote Method Invoke): Calls a method on a distant object. It makes use of serialization to transfer data from the client to the server. RMI, which is a lower-level protocol, is used by EJBS.  
• JTS (Java Transaction Service): The fundamental kind of CORBA OTS transaction monitoring is JTS. The implementation of the transaction manager is described by JTS. The Transaction manager is a Java Image that implements the OMG OTS specification at a low level while supporting the Java Transaction API (JTA) specification at a high level. Application servers, resource managers, standalone programs, and communication resource managers can all use the transaction services offered by the JTS transaction manager.  
• JSP (Java Server Pages): HTML and embedded Java Code make up a JSP page. After the client requests the page, the server executes the Java code and sends the produced HTML page to the client's browser.  
• Java Servlet: A web server's functionality is increased by a tiny Java software known as a servlet. It is executed on demand as a server-side program, much like a CGI Perl script. JSPS and servlets both offer similar capabilities, but servlets are implemented differently, while most HTML code contains a small piece of Java code called JSP, servlets are written fully in Java and produce HTML. 
• EJB (Enterprise JavaBeans): EJB is one of the factors that have contributed to J2EE technology receiving so much media attention. They offer a framework for creating and putting into use distributed business logic, greatly streamlining the creation of scalable and intricate enterprise systems. When and how EJB components interact with their containers are specified in the EJB specification. Common services like directory services, fault tolerance, transaction management, resource buffer pools, and security are provided by the container.

Since its initial release in 1999, J2EE has grown to become a comprehensive standard for developing and deploying portable, multi-tiered enterprise applications. The open-source process used to create the J2EE platform is partially responsible for its success (the Java Community Process). The J2EE framework has advanced more recently to incorporate the rising popularity of web services. New features and improvements to foundational J2EE technologies like JavaServer Pages (JSPs), Servlets, and Enterprise JavaBeans are included in the J2EE 1.4 platform.

However, the support for web services, which J2EE 1.4 supports, is the most intriguing new feature. These standards include UDDI, SOAP, WS-1 Basic Profile 1.0, and WSDL. A special platform for developing, deploying, and managing web services and enterprise applications is made possible by the combination of J2EE 's portability and web service interoperability.

To deliver the most recent web services features, it is possible to integrate the application server with the company IT infrastructure using the J2EE 1.4 platform. It allows companies to make their current J2EE applications available as web services. Both Java-based and non-Java web service clients can access exposed Servlets and Enterprise JavaBeans (EJBs) as web services.

Regardless of how they are implemented, J2EE applications can interact with other web services and operate as their web service clients.

The J2EE 1.4 Software Development Kit (SDK) gives the resources needed to design, test, and deploy web services and clients that communicate with other web services and clients that are operating on platforms with or without Java technology. Businesses can also expose their current J2EE applications as web services thanks to it.  

Web service clients using Java technology or those using non-Java technology can access components such as servlets and Enterprise JavaBeans (EJBs) as web services. Regardless of how they are implemented, J2EE applications can interact with other web services and serve as their web service clients. 

J2EE Standard Tools will include plug-ins for creating J2EE applications and will support creating, testing, and debugging J2EE applications on a variety of J2EE servers.  

The J2EE tools will consist of: 

• Service Tools. 
• More than simply launching a Virtual Machine (VM): 
  • Sophisticated environmental configurations and class loader models. 
  • Local and distant development scenarios are in progress. 
  • All J2EE compatible servers must be supported. 
    • Extensions used to manage exceptions. 
  • Run, Stop, Restart, Profile, and Debug Launchers. 
  • Editors and Wizards for Configuration, starting, halting, troubleshooting, and restarting applications servers.  
• J2EE Modules Tools 
  • EAR, RAR, WAR, EJB-JAR 
    • Web Applications, EJB, business software 
  • Assemble Modules 
    • Imports from Wizards 
  • Build modules 
  • Verification modules 
  • Edit modules 
    • Descriptors for deployment 
    • Packaging components 
  • Connection modules (ears) 
  • Support for server deployment  
• J2EE Components Editors 
  • JSP 
    • Standard editor for coloring, code assistance, refactoring, and formatting. 
    • JSR-45 Troubleshooting 
    • Content-based selection 
    • Hybrid editing 
    • Build Participation 
  • EJB Tools  
    • Code generation using Annotation  
    • Wizards 
    • Validation 
  • Web Services for Java 
    • Axis Adapter 
  • Navigational Tools  
    • J2EE Viewpoint(s) 
    • Module Views 
    • J2EE Frameworks 
    • Servers 
• J2EE Development Process Tools 
  • Testing Tools 
    • Unit and Integration Testing 
• Performance Tools 
  • Profiling  
    • Stress and Load Testing

Enterprise Developers and IT Companies. Reusable J2EE components give enterprise developers and IT Companies more competitive options. They can put together applications using a combination of common, commercially accessible components and their own unique components thanks to the J2EE framework. A variety of standardized J2EE functionality is readily accessible off the shelf, ranging from generic business application components to vertical market solutions.

An e-commerce site may be created by combining pre-made EJB components for shopping cart functionality, updated EJB components for specific customer services, and entirely customized layouts using JavaServer Pages technology to give the site a distinctive feel and look. 

The abbreviation EJB stands for Enterprise JavaBeans. It is based on JavaBeans technology and is a component of the J2EE platform. A server-client approach underlies the operation of the server-side platform known as EJB. This platform offers the software building blocks needed to create distributed and reliable business applications.  

The majority of the software’s components are written in Java. EJBs, Java application servers, and EJB containers make up the EJB architecture. Here, the EJB container essentially serves as a runtime environment where EJB applications can be run, while the Java application server is used to run the EJB container.  

EJB mostly concentrates on the applications’ business logic. An application’s basic functionality is represented by business logic. EJB can be used to streamline complex commercial applications. Additionally, you may easily create and implement extremely scalable and high-performance applications.

The architect is in charge of imagining the behavior of the system and designing a blueprint for it. The architect determines how the system’s components interact, as well as establishes and incorporates both functional and non-functional needs. This develops the infrastructure required for the system to function properly.  

The multi-tier architecture of the J2EE which comprises the Client Tier, Middle Tier, and EIS Tier, can only be understood by a J2EE architect in order to successfully create a platform for the creation and deployment of web applications for enterprises

1. Database field mapping and persistence management: Most database mapping may require logical comparisons, string operations, mathematical computations, and some other data modifications to be carried out by the bean developer.  
2. Manage security by defining users, groups, and roles: To efficiently manage security in a Java Client, the bean developer is required to create groups and roles and then add users to them. A group is a collection of users with common responsibilities or functions, for example working in the same faculty in a company.  
3. Creating Wrapper class: A class whose object contains or surrounds primitive data types is known as a wrapper class. Primitive data types can be stored in a field that is created when an object to a wrapper class is created, meaning it is possible to create a wrapper class object out of a primitive value.  
4. Using Deployment Tools: The responsibility of the Bean Developer is to select the Deployment Tool best suited to the assigned task. One of the most important phases of the software development life cycle is deployment, which may be thought of as the beginning of the application. Thus, one of the key elements in the development of software is the deployment tool selected.  
5. As technology evolves, a variety of sophisticated Java deployment tools have been created. These tools offer solutions to various tasks like automatically creating and testing codes, and supporting appropriate error monitoring.

EJB stands for Enterprise JavaBeans, it is a technology that encourages a basic approach to the development of multiplier applications thereby, mitigating app complexities and boosting the featured designer to place more attention on the business logic.

This platform manages state and transaction functions, collates resources, and performs basic research actions and multithread executions, thereby leveraging the developer and permitting creators to focus on actual business logic designs.

It also gives creators the chance to model the entire variety of objects useful in the enterprise by specifying the types of EJB components that may exist, they include: 

• Periodical beans 

They are also called ‘session beans.’ It describes the behavioral patterns related to the specific customer session like it can function as a service-web termination point during user purchase transactions on an electronic purchasing site. 

It executes the task for the client and incorporates the business logic that allows programming which can be activated by the client. The types of session bean are stateful, stateless, and singleton periodical beans. 

• Structural beans  

Referred to also as ‘entity beans’ and it represents data collection, for example, data on the row or column of a database, it then incorporates operative features of the specific features they stand for. The main aim of structural beans is to persist for as long as the data they represent exists. 

• Information beans 

Also called ‘message-driven beans.’ They permit the J2EE apps to process information received in an asynchronous format. They behave like event listeners that instead receive Java messages forwarded by any application feature component which could either be a customer, a web feature, or an enterprise bean. It could also be gotten by other non-J2EE technological apps. It listens for specific message types like that from Java API servers. 

This is one of the most frequently asked J2EE interview questions for freshers in recent times.

The benefits of the Java 2 Platform, Enterprise Edition (J2EE) are inexhaustive, below are a few of such advantages derived from its use. 

Movable 

The J2EE app is not device or interface-dependent, this means if the application was designed on one device, it poses no difficulty when transferred to another platform or device for use. It remains intact and functions the same way as it would on its home platform where it was designed, so long as the receiver platform is J2EE -friendly. It delivers the “develop once, run everywhere” feature. 

The application has been preferred as it minimizes the difficulty often encountered when programmers attempt to move an application from one platform to a new and unfamiliar one. For instance, when transferring a software app from its production platform to the user-display premise for auditing. 

Recyclable 

The J2EE interface is made of different modules which can be reused in the making of subsequent applications. This reduces the sizes of applications that would be expected since the individual aspects are not made of freshly written functionalities. An example is the reuse of a database reader on another application which would be appropriate and function just fine, instead of building one from scratch for each developing J2EE -compatible application.  

Since the J2EE features can be reused, it boosts competitive preferences for developers of enterprises and IT businesses because the platform enables them to couple applications from a combination of numerous standard available sources, giving them the leverage to customize a range of efficient functionally off-shelf applications.  

Reliable 

A good number of requirements necessary for the smooth running of application platforms are built into the J2EE platform which makes it easy to use less because it does not require combining multiple platforms to get the job done. This time is saved on development processes with high-quality release products that are portable and durable, which ultimately results in increased efficiency of production processes and an enhanced turnover rate to the organization. 

Confidential 

Using the J2EE model platforms helps keep private and official documents safe and secure and gives developers the luxury of protecting highly sensitive files and documents than they would have been able to do with the use of other lesser applications. 

Adaptable and User-flexible 

The applications built via the J2EE technology are scalable and can adapt to the diverse Java-friendly interface, regardless of their sizes and processing capacities. The J2EE platform accords the developers and users the liberty to choose graphical interfaces within an organization's net frame or the global net. Clients can use the platform on a vast range of different gadgets like phones, laptops, and desktops, they can also run them via pure user-based interfaces like the basic HTML and Java applets. 

Through the interventions allowing the support of user-based interfaces for running the J2EE technology, there is room for the development of faster prototypes, individualized Java application clients, and those that support a wider range of end-users. Furthermore, the J2EE model allows for an automatic download feature when the Java-plug-in is activated and incorporates a support applet where required.

The J2EE model has numerous specifications that function in different scenarios like developing web pages, interpreting data from databases, and coordinating and organizing distributed queues. These are a function of the different technologies that the J2EE provides, and they are explained below, together with their features. 

Java Servlet (JS) Technology 

The JS-technology are Java based applications that run on Java servlet web servers in which developers create dynamic webs used to manage the requests made on web pages from a browser, send feedback of processes returned to the browser, and implement behaviors that are server-sided which utilizes the full powers of the Java APIs. 

Computer Generated Imagery (CGI) experiences drawbacks because it creates a different request each time it is handled by a CGI user program. This means that with an increasing number of users, a new process must be generated for every request made by these users, thereby wasting time and resources. As opposed to the CGIs, the JS technology does not possess this pitfall because the servlet applications are run by different threads. 

Java Server Pages (JSP) Technology 

The JSP involves developing processes that are server-sided which enables the generation of dynamic applications based on specific web designs. Examples the very popular HTML interface together with the ability of server-side change generator content.  

The updated JSP 2.0 model supports fixed templates, simple Java items, and easy flexibility. 

The features of the JSP technology are outlined below: 

• Java tags user embed Java codes within HTML which markedly increases performance such as <%--JSP code--%> 
• Possesses access to Enterprise Java APIs  
• Incorporates the use of servlets also on its JSP pages  
• The embedded code pages act in dynamic fast fashion online registration forms or dropdown boxes. 
• Java Beans Objects (JBO) can be accessed by JSP technology 
• Distinguishes the logic interface from a presentation layer 
• Simplifies the generation processes of dynamic web containers. 
• Handles all dynamics within the containing web  
• Does not need additional web features 

Enterprise Java Beans (EJB) Technology 

This architecture is used for developing highly resizable and huge applications at enterprises. 

Its features are: 

• Focus on the application's business logic since the app server generates the majority of the interactions at the system level. 
• It has a container that organizes all of its activities 
• Its components can function effectively on any friendly interface and are not solely dependent on their home platforms 

The types of EJBs are: 

• Periodical/ Session 
• Structural/ Entity beans 
• Information/ Message-driven beans 

Java Database Connectivity (JDBC) Technology 

This particular technology connects and implements queries using the JDBC drivers like the native, protocol, thin, or JDBC-ODBC link drivers. The JDBC technology features are: 

• Non-platform dependent 
• Can function in the development of different types of executable apps such as the JSP, EJB, Servlets, and Java applets 

Java Message Services (JMS) Technology 

The JMS functions as an API that provides messaging services by acting as a communication media between different systems in a particular network.  

Its features:  

• Conjoint or disjointed mode message exchange 
• It has APIs that permit operations to synchronously run between the JMS and other platform languages 
• Apps developed on message queues, sender and receiver concepts 

Its domains are: 

• Point messaging  
• Subscribe messaging

Java Transaction API (JTA) Technology 

This gives room for the distribution of performing transactions used to edit and update data by numerous computers functioning under a network. Its server controls the access granted to resources in the shared space. 

It provides the following features: 

• Automation of transaction processes 
• Preservation of data integrity despite a failed transaction 
• Consistency in transaction processes 
• The commitment of provided applications to transactions 

Java Mail Technology 

This API technology is used to develop and interpret emails. Their features are; the interdependencies of both protocols and platforms. 

Java Naming and Directory Interface (JNDI) Technology 

This API is used for naming and directory services that permits the discovery of specifically named data. 

It has the following features:  

• Execution Independence 
• Service Provider Interfaces (SPI) 
• Establishing links between Java apps and directories located externally 
• Name object binding technologies 
• Clients event interface 

J2EE Connector Architecture (JCA) Technology 

It is a standard system that establishes contracts between the app server and adapter framework. It is used to set up connections between applications and the EIS.

This is one of the most frequently asked Java J2EE interview questions for freshers in recent times.

For each J2EE technology, there are different components of the application's architecture, these are outlined and explained below. 

Java Servlet Architecture 

The JS technology includes the following architectural execution processes: 

• Request order is made and sent by the client 
• The request order is received by the web server 
• The request order is translated to the corresponding server 
• The servlet interprets and processes the request 
• Servlet generates output responses 
• Servet feedback on the web server 
• The web server sends a response get back to the client  

Java Server Pages (JSP) Architecture 

The working architecture of the JSP technology performs an important function in the management and processing of a client's request order through the following steps. 

• Request order is made and sent by the client 
• JavaBeans Object (JBO) is generated by the JSP technology 
• Request orders are processed by the JavaBeans through important data from the database where applicable 
• The response is forwarded and returned to the client. 

In a second architectural framework, Servlet functions as the control 

• Request order is made and sent by the client 
• The request order gets processed by Servlet 
• Servlet generates the JBO and opens a specific JSP interface 
• JSP has no place in the processing of a client's request order and just functions in the aspects of the presentation. 

Enterprise Java Beans (EJB) Architecture 

The EJB architecture in its simplest form involves  

• Receiving the client's request order 
• Processing of the requested order by the EJB technology 
• Feedback to the client 

Java Database Connectivity (JDBC) Architecture 

This architecture is sectioned into two forms; the 2-tier and 3-tier architectural designs. 

2-Tier Java Application Architecture 

This architecture accesses the interface database directly within the JDBC driver. This database may be found within the same or a different platform in the configuration established for the client. 

3-Tier Java Application Architecture 

On the other hand, the 3-tier architectural requests are delivered to a third party, otherwise called the middle-tier, that processes the order and directs it to the data source which in turn processes it and forwards it back to the middle-tier before it finally is sent to the client. This architecture controls data access methods and additional updates attached to the enterprise data. 

Java Message Services (JMS) Architecture 

The architectural framework includes the following 

• Object event wave 
• Spirit waves 
• Inter agent event 
• Sun Java Message  

Java Transaction API (JTA) Architecture 

This architecture includes two managed transactions 

• Container transactions 
• Component transactions 

Java Mail Architecture 

The JavaMail architectural framework includes the following: 

• Post office protocols (POP) 
• Internet Message Access Protocols (IMAP) 
• Multiple Internet Mail Extension (MIME) 

Java Naming and Directory Interface (JNDI) Architecture

• Access protocols for directories 
• CORBA ( Common Object Request Broker Architecture) 
• Services for Common Objects 
• Remote invocation methods for Java 
• Service name domains 

J2EE Connector Architecture (JCA) Architecture

The JCA architecture includes the tools for managing, and they include the following: 

• Connection managers 
• Transaction managers 
• Confidentiality managers 
• Lifecycle managers 
• Work managers 
• Transaction Inflow managers 
• Message Inflow managers 

The J2EE components are application parts incorporated into different client applications about the diverse tiers in the multi sectioned J2EE platform. These components of the J2EE are self-sustained action units located in the J2EE application acting either independently or coupled to combine corresponding files that facilitate communication between the components and the J2EE application. 

There are four main components of J2EE applications namely: 

1. Client Tier 
2. Web Tier 
3. Business Tier 
4. Enterprise Information System (EIS) 

Examples of client tiers are client applications and applets which run on a client-user platform. The web and business tiers include components like the servlets and server pages (JS and JSP) on the J2EE server. The Enterprise Information System (EIS) component operates on its personalized server, the EIS server. 

Note, the features of Java components can be distinguished from Java program features because the former are only parts and needs to be coupled under a J2EE compliant specification platform and managed by the J2EE servers after they are delivered. 

Expect to come across this, one of the most important J2EE interview questions for experienced professionals in Web Development, in your next interviews.

A J2EE module is a software storage unit made up of multiple components aimed to be released under the same container type upon delivery. J2EE module can easily be released or coupled into J2EE applications. The types of J2EE modules are: 

• Client Application Module

This module is made up of class-level files and descriptions for client app release which are coupled as JAR files with the code .jar extension. 

• WEB Design Module

This design module contains JSP files, class-level files, and descriptors for web-web release files for Graphics Interchange Formats (GIFs) and Hypertext Markup Language (HTML). All these files are coupled as a JAR file with a war (Web Archive) inscription .war extension. 

• Resource Adapt Module

The Resource Adapt Module incorporates the level classes, Java platforms, native spaces, release resource adapt descriptors, and some others into rar ( Resource Adapter Archive) JAR files tagged .rar extension 

• Enterprise JavaBeans Module

This module contains the level-class files specific to EBs (Enterprise Beans) and a developer for EJB descriptor, they are all packaged as JAR files with the code .jar extension.

A client in the J2EE application functions on a platform that aids handling which requires a better or more complex user interface than that provided. The Java client is simply developed to operate within the JVM (Java Virtual Machine) located on a client's gadget, for instance, a laptop, phone, and others. Various client types support J2EE technology. 

Web or Thin Clients

This client works without the aid of a query database to operate cumbersome enterprise rules or to attach legacy apps by downloading complex systems to the enterprise beans operating platform on J2EE where they perform better by utilizing special features like high speed, high confidentiality, and reliable features. 

The thin client has two aspects namely; 

• Dynamic web interface that is made of different encoding markup languages such as HTML, XML 
• The web browser that attends to the requests gotten from the servers. 

Application Clients

These clients operate on provided client machines and different task execution processes available that may need a complex high-yield user interface which can be provided by a language markup. Application clients have direct access to the EJB components in the system servers, but if the application requires access, the J2EE client app can open an HTTP link to create a connection for communication background servlet web browser. 

Web Services Clients

This includes applications such as the sun Java system which enables the sending and receipt of applications from certain web services which are activated by the construction of SOAP messages across HTTPS, for example, the SOAP Apache app 2.2. They also have built-in support for these clients' web services which are coupled to the application servers of the Java framework. 

Java Message Service (JMS) Clients

The JMS clients are program language plans for JMS providers used for information dissemination. This client can be made of any J2EE . For instance, it could be made of a web app, container client, or an EJB feature. In this case, a specified type of EJB is assessed, which is the message-driven beans via the JMS by transporting information to the JMS endpoint.

Common Object Request Broker Architecture (CORBA) Clients 

These are clients' apps documented in CORBA-supportive languages such as languages used in Java programming like C++ and C. These clients can be used when unsupported programs or certain application servers are uploaded to the system application servers.

JDK signifies Java Development Kit while JIT represents Just In Time Compiler.  

The JDK possesses JREs (Java Runtime Environment ) which is an executed JVM ( Java Virtual Machine). Together with the JREs, it contains other tools for development such as  

• Libraries 
• Compiler tools 
• Debugging tools 
• Bundling tools 
• Tools for deployment 

While, the JIT (Just In Time Compiler), is an aspect of the JVM used to boost and shorten the program execution time. It combines and collates the components of similar functional code bytes at the same time, thereby, shortening the compilation time. 

‘The compiler’ here represents a media that interprets the set of instructions on a JVM into specific sets of instructions for the processing units.  

The JIT is activated to run after commencing the execution of the program, on the fly interface. The JIT has permission to information on the runtime and optimizes the codes to improve the efficiency of performance.

A must-know for anyone looking for top J2EE interview questions for developers, this is one of the frequently asked J2EE interview questions.

The concept of PATH and CLASSPATH in J2EE can be a bit confusing and may be mistaken for each other, but they are different and not interchangeable.  

The major distinguishing attribute is that PATH is used in Java-based programs to compile codes, whereas, CROSSPATH is utilized by application loaders to discover, compile and upload Java bytecodes that are kept in the .class file 

1. Centralization: A multi-tier client-server architectural model’s main advantage is that it enables centralized management. It is easy to obtain all the necessary information in one location. This is quite advantageous since the network administrator has total control over management and administration. Any problem that emerges across the entire network may be fixed in one place. In addition, updating data is made simpler. 
2. Flexibility: Users can quickly increase the number of servers or clients. There are no issues with authorization to expand network resources because the server is centralized. As a result, the installations only require a few individuals. 
3. Security: Data is effectively protected because of the multi-tier client-server architecture model. Therefore, it is possible for only authorized users to access the data with login and password as well as two-factor authentication. Additionally, if the data is lost, a single backup can quickly restore the records. 
4. Operation – Since all files are stored on a single server, handling them is easy. The required file records can easily be monitored and assessed using a client-server network.

A build file is a set of instructions that explains how to link and compile the several independent files that make up a program. It specifies to the compiler which libraries and frameworks to be included in a program as well as the various versions.  

In addition, it can define the build settings like which optimizations to use or whether to include a memory and limit check, as well as other optimizations settings. It is also used to automate the process of creating a software build and any related task such as converting computer source codes into binary codes, running automated tests, packaging binary codes, and publishing located source codes to a central, shared repository.  

It is very important to make DevOps operations effective while saving effort and time, mostly for the Continuous Integration/Continuous Development (CI/CD) strategy, which is one of the seven DevOps principles to be employed, making Build File very important in DevOps.

EJB stands for Enterprise JavaBeans, commonly known as server-side software components; it will be mostly used as the business logic for the applications. The software components, servlet lifecycle management, web services, computer security, and transaction process are some of the web containers utilized for runtime environments.  

Since the client-server architecture style known as EJB operates on the server side of the computer network, it has been included in apps. Additionally, EJB, a JavaBean technology, is used to distribute web components on the client side and provides the ability to reuse components across different web applications. 

How Does EJB Work In J2EE ? 

• The JavaBean class will employ many annotations for the EJB specifications in EJB, which will be useful for meeting user needs based on business objectives. EJB has a unique set of versions and has adopted the Java Naming Directory Interface (JNDI) feature.  

The directory service, which is one of the resources on servers using JNDI, is used to find or allocate resources like EJB, data sources, and JMS queue services. The servers have a default scheme name for the JNDI resources, but if we modified the name of the configuration portion, it should be overruled.  

• Java beans will function with EJB, which has two varieties which are session beans and message–driven beans. Client-server interactions will use session beans, which encapsulate the application’s business logic through programmatic client invocation on either a local machine or a distant machine. Web services will be used by the client to access the bean.  

There will be three distinct sorts of session beans which are Stateless, Stateful, and Single. Stateless beans are thread-safe and execute much more quickly than stateful beans since there is no permanent state in web containers when the client uses these types of beans. Multiple clients simultaneously share these beans.  

• Stateful beans have the ability to store the states in containers; when the client ends the session, the server also deletes these states. Singleton beans exchange their states with numerous clients and have a single instance session over the life of the application. These beans perform quickly in comparison to stateful beans since they are thread-safe, making development easier.  
• Similar to JMS message listeners, Message Driven Beans (MDB) are used as asynchronous message receivers, but they receive message responses as JMS messages as opposed to events. Every time the container calls the MDB beans using the onMessage() method after receiving a message, we can map the messages using JNDI services.  

Using the onMessage() method will result in a single transaction for the whole MDB process. The recipient message is once more redelivered if the message procedure involves a rollback.

Don't be surprised if this question pops up as one of the top J2EE interview questions for senior developers in your next interview.

Similar to how an image is placed on a website, a J2EE applet is a program created in the Java Programming Language that may be added to an HTML document. When a page is accessed with an applet using a browser that supports Java technology, the applet’s code is downloaded to the computer and run by the browser’s Java Virtual Machine (JVM).

J2EE applets are used to help a user create applications that are more organized and modular by using web components. They offer a means of decoupling application programming.

The Struts architecture is built using Model View Controller (MVC), the most well-liked Java application design idea. Model View Controller, often known as struts, is a design pattern that is used when you wish to separate the presentation of application data, user interface elements, and business logic in your application.

The program becomes reusable and expressive as a result of the MVC design for struts. With it, users don’t have to start from scratch when a problem arises and some sort of change needs to be done. Once the pattern is known, which is easily learned, it is possible to change it when needed.

The strut architecture is made up of the MVC pattern as well as a number of other elements that make up the framework.  

The Model contains the business logic of the code and is in charge of processes involving data, such as access to the data, validating it, and determining how it will be saved in databases or data stores.  

The View is in charge of everything that the user will be able to see. It also collects all necessary user inputs, generates requests that should be submitted to the controller for handling, and accepts the controller’s replies, which can then be displayed on the user’s screen. When using the View component of the MVC framework, it is possible to use HTML, resource files, and custom tag libraries.  

The Controller serves as a bridge between the View and the Model. It is in charge of organizing and managing every request that comes from the user-facing view side. The controller starts a specific piece of business logic code as soon as the request comes in, handles the Model structure, and then sends the appropriate data to the View in the form of a Model.

The term “ORM” refers to Object-Relational Mapping, which uses objects to link a programming language’s database systems with the ability to apply principles from object-oriented programming and SQL. Any database management system where object mapping to the table can be accomplished in the virtual system is capable of supporting ORM implementation.  

ORM goes together with Database Abstraction Layer (DBAL) because ORM prevents users from writing code that contains database queries. Instead, it only allows users to work with objects belonging to particular classes that correspond to database records. The ORM class completes all database queries in a fully transparent manner.  

Another principle of ORM is not starting from scratch. Every programming language has open-source ORM libraries available. Usually, these libraries give a superclass that resembles a “database object,” from which it gives other classes.

A collection of web platform APIs called web components allows users to build new, reusable, encapsulated HTML elements that can be used in web pages and online apps. These Web Components are made up of: 

• HTML Templates: Used to declare markup when a page load is specified by the HTML <template> element. In other words, it is possible to store some markup on the page using the template element, which can be copied and reused. To specify how the component is to be rendered in the browser, enter HTML and CSS code inside the <template> tag.  
• Shadow DOML: Hides all custom element markup and styling.  
• HTML Imports: Includes HTML documents into one another. The link element’s rel attribute is given the import keyword.  
• Custom Elements: Construct new HTML tags thanks to custom elements. This is done by creating a new element, improving already-existing HTML tags, or extending components created by other programmers. 

Although the four components are intended to function as a whole, it is also possible to utilize each one alone. 

JSF is a user interface framework written with Java, that is based on server-side components. The creation of web applications uses it. It has robust API and tag libraries and offers a clearly defined programming model.  

Components are added to web pages, and connections between components and server-side objects are made using the JSF Tag libraries. Additionally, it includes tag implementers that handle the component tag. These capabilities and tools allow users to quickly and easily construct the server-side user interface.

Java Bytecode is loaded, validated, and executed by the Java Virtual Machine (JVM). It is referred to as the interpreter or the core of the Java Programming Language, as it executes Java code. Both JDK and JRE require JVM, which is specifically in charge of turning bytecode into machine-specific code. JVM also carries out a bunch of tasks like memory management and security. It can also execute programs that have been converted to Java bytecode from other programming languages.  

JIT is a crucial component of the JVM in Java. It greatly speeds up execution performance compared to the previous level. In other words, the greatest performance environment is provided by a lengthy, computer-intensive program. At compilation or runtime, it improves the Java application’s performance.  

Java Development Kit (JDK) is a software development kid, frequently referred to as a superset of JRE. The creation of Java applications and Java applets is made possible by this fundamental component. All the tools needed to compile, debug, and run a program created on the Java platform are included in JDK.  

The Java Runtime Environment (JRE) is a group of software programs in charge of running Java programs and applications on a computer. JRE is only required when installing applications, and not writing or compiling code.

• User Interaction: The user experience needs to be seamless and compatible with a range of gadgets, such as laptops, mobile phones, etc.  
• Data Connectivity: In order to enable business activities, a J2EE application’s connection to legacy systems must be reliable. 
• Service Availability: To ensure that the application is accessible 24/7 in order to fulfill essential business goals. 
• Easy Access: Applications should be simple to use and accessible on any device and from any location.

The Java-specific, steam-based protocol known as Java Remote Method Protocol (JRMP) looks up and references remote objects. Java objects are necessary on the client and server sides. It is a wire-level protocol that utilizes TCP/IP and RMI.

Below table reflects the difference between the J2EE and Spring. 

This is a common yet one of the most important J2EE interview questions and answers for experienced professionals, don't miss this one.

Client, EJB, and web components are all included in the compressed and bundled file known as an Enterprise Archive File (EAR). It has the extension .ear. Using EAR files, it is possible to deploy numerous modules to the application server at once.  

A file that has been compressed and packaged together with all web components is referred to as a WAR file. With just one request, this file makes it straightforward to test and publish web programs.  

A JAR file is a Java Archive File. It contains each class file and library that an API is made up of. These are compressed and bundled together in the .jar file. These are used to deploy the entire application, including classes and resources in a single request.

• The 64-bit JVM is used by 64-bit operating systems as opposed to 32-bit operating systems.  
• As opposed to the 4G cap of the 32-bit JVM, the 64-bit JVM allows a bigger heap size of up to 100G.  
• Java programs use more memory when operating in a 64-bit JVM than when running in a 32-bit JVM. This is due to the larger size of the Ordinary Object Pointer.  
• The 64-bit JVM uses 12-byte object headers and a maximum of 8-byte internal references, as opposed to the 32-bit JVM’s use of 8-byte headers and a maximum of 4-byte internal references.

Struts is an enhanced web application framework with a no-limitation source that broadens the Java Servlet Application Programming Interface (API). It was formerly known as Jakarta Struts when it was created by Mcclanahan Craig in the year 2000 and donated to the foundation, Apache, which was replaced in 2007 by the Struts 2. 

Struts frameworks are large frameworks used to develop business-large apps with designs that are easy to use. They are referred to as the legacy that should be adhered to if subsequently required by the user. 

The Struts Framework: 

• The struts framework provides the Action and controller servlets, which are incorporated into the libraries and Integrated Development Environment (IDE). They are included in the frameworks Extensible Markup Languages (XML) and on boarded onto a standard architectural platform known as the Model, View, Controller (MVC), which is used to develop the Java 2 Platform, Enterprise Edition (J2EE ). 
• This model (the addition of logic to interrelate with the available database) is distinguished from the view (which is the HTML page seen by the user) and controller.  
• The servlets are used at the commencement of the project. The action series develops the displayed user templates, while the controller servlet delivers the information between both view and model users.  
• Struts configurations are established by programmers such as config.xml which maintains the model, controller, and view display. 
• Servlet maps are then used to demand Struts Action Objects (SAOs) using the earlier established configuration. 
• In the event of an information alteration, an update to the Extensible Markup Languages (XML) file would be sufficient. 
• Data is stored momentarily as Action Form Objects (AFO), and orders are executed. 
• A string (Action Forward) is brought back by the Model to build the controller and direct it to forward an output page to the user. 
• After processing requests, Action Objects sorts out new data and sends the results to the right display point. 
• The JavaBeans form is then used to pass information about the model and client pass. 
• The library custom tag is used to document the content of the beans, thus the Java code will not be needed. 
• Struts templates called the “Tiles mechanisms” are then used as a layer for representation. 
• The Java annotations are used to represent information to create applications that can be integrated into other frameworks. 
• Anytime an order is placed, an action is created and the servlet answers the model calls. 

The use of struts is simplified by the provision of UI, control, and action tags. 

• The Strut themes  
• HTML (Default theme) 
• css_html  
• simple 

Advantages of Struts in the J2EE Framework 

• The struts framework assists in binding received files with enterprise logic and the display of deliveries using HTML.  
• Struts encourages the development of flexible, adaptable, and sustainable apps built on strong technological standards like the Jakara Server Pages (JSPs), JavaBeans, and Extensible Markup Languages (XML). 
• Due to the Model, View, Controller (MVC) framework, it is easy to use, efficient, and easily understood by developers and has less creation time. 
• As a result of XML and property files, changes can be made to files without having to alter the original Java code. 
• It aids developers in properly maintaining documentation.

Before designing an Interactive User Interface (UI) for J2EE apps the following points should be considered. 

• Knowledge of the proposed users 
• The simplicity of the interface 
• The need for consistency, standard, and the application of common UI elements 
• An efficient and flexible page layout 
• The resourceful use of graphic textures and colors for aesthetics 
• Clarity of design 
• Freedom for user-based control 

The J2EE interface gives rise to a group of minimal-level routines in form of servlet APIs that allow developers the opportunity to directly design the release that is streamed into the search interface. The APIs serve as the foundation for which the hierarchical layers are set, which include the Interface displayer, and front controller feature needed for a common several-paged application, all these simplify the dynamic output release. Also, the UI and controller framework possess many different attributes which serve several functions.  

Several UI technology methods exist when creating a J2EE application 

• JSP 
• JSF (JavaServer Faces) 
• Basic HTML 5 and JavaScript 

There are different conditions to use the above UI technologies based on the benefits of one over the other in a given scenario. 

One of the most frequently posed J2EE scenario based interview questions, be ready for this conceptual question. Here is how to approach this question -

HashTables are: 

• Also called hash maps 
• Value map keys embeds the class of the dictionary, and maps keys to values. 
• The values contained in the hash tables are based on the keys.
• It uses a hash feature to collate an index called the hashcode which is input into a collection of lists, each of which serves as a todo called ‘bucket’, and its position is identified by calling out the method of the hashcode(). 
• During a search, the key is hashed and this shows where the respective value is kept. 
• The J2EE hashtable class possesses specific and unique elements, prevents null values or keys, and can be synchronized

The workings of J2EE  

Hashtable was previously a part of the main Java and is a standard dictionary implementation. J2EE was designed with the hashtable added to its framework also to implement a map. It saves keys and values in the hash table.

During the utilization of a hashtable, the following steps are taken: 

• Indicate the object to be used as a key 
• Incorporate the value you like to include in that key 
• Hash the key 
• Use the generated hashcode as the index (that is, where the values are saved on the table)

Available Constructors In The Hashtable Class 

Example of a hashtable for a mini-client book 

In a normal setting, the hash function assigns a specific bucket to each key, however, in certain instances, some hash table designs utilize a flawed hash function that may result in a hash collision where the function develops an exact index for different keys.

Properly dimensioned hashtables have lookup times that are not determined by the number of elements on the table. Also, some designs permit alterations like additions and deletions to be made to the value-key pairs.

Hashing best describes the concept of, a space-time trade-off where an infinite memory exists and all the keys on a table can be used directly as an index to look up their value within one access memory. Alternatively, where an infinite time exists, values can be saved without considering their keys, and elements can be retrieved utilizing a binary or linear search. 

Hibernate is a powerful framework used to keep and retrieve data from a Java platform to a database table. It is a high-operational Object-Relational Mapping (ORM) tool in J2EE that maps classes to tables, often in rows, and assigns values to mapped table columns. It is also used to map various J2EE data types to the SQL. Hibernate translates the HQL queries into the usual SQL queries, which subsequently the database actions.

It is a persistence platform, that stores data permanently to storage platforms like SQL databases and fetches them back at any period such as towards or after the end of the execution processes.

Hibernate-supported databases include: 

• The MySQL database 
• PostgreSQL database 
• Oracle database 
• DB2/NT database 
• Sybase SQL server database 
• Microsoft SQL Server Database and others. 

The Architecture of Hibernate: 

There are 3 available configurations in Hibernate; 

Hibernate.cfg.xml 

It is an XML file that is saved and rooted within the application's classpath, and this file is what encompasses the Hibernate configuration. 

Hibernate.properties 

It is a property file that bears the pair of value-keys for the various Hibernate configurations. 

Program configurations 

This represents the Java file configurations that are to be done manually. 

Hibernate Query Language (HQL) is a type of query language of the Hibernate framework that operates with the use of recurring objects and their persisting properties. The syntax of HQL is similar to that of the SQL but differs in that it executes object and property operations of classes that are persistent instead of using columns and tables, however, the SQL statements can be used directly in the Hibernate framework. 

The Hibernate framework converts the queries in HQL into specifically designed databases to execute specific actions. The query platforms are the techniques and feature functionalities required to display, operate, and navigate the HQL query in an object-defined manner. 

Certainly, there are drawbacks to the use of Hibernate, despite its high performance and exquisite nature. 

• Need to learn numerous APIs 

The daunting task and enormous effort required to learn Hibernate APIs stands as a discouraging factor, although Hibernate in itself is a simplified framework to use, however, it is often tasking to learn how to use it.  

• Difficulty Debugging 

With Hibernate, oftentimes, debugging files to optimize performance may be challenging. 

• Slower than a Java Database Connectivity (JDBC) 

Due to the numerous SQL statements generated by Hibernate during its runtime, this slows down its activities such that a basic JDBC seems faster in application compared to Hibernate. 

• Not recommended for Batch processing 

The basic JDBC is what remains recommended for batch processing for better functionality. 

• Unsuitable for minimal projects 

Small and less-sized projects are those with fewer tables and columns, this defeats the aim of using Hibernate, hence it is unsuitable and unrecommended. 

• Prevents multiple inserts 

Using the Hibernate framework negates the application of some types of queries that are not JDBC-supported. For instance, it prevents the addition of multiple insert objects like persistent data to the database using the same particular query. Hence, a developer will be required to write a different query for individual objects. 

• Develops complex queries 

Hibernate generates several joint queries causing multiple query conversations for complex data. The recurrent mapping between objects and queries results in a reduction in the level of performance and prolonged query conversation time interval.

These are the benefits of using Hibernate: 

1. No new written code is required to map it because it operates the mapping of the J2EE data classes to the table of the database using configurations, annotations, or an XML file. 
2. The objects in this Java tool can be directly saved and retrieved by the application of the framework's simplified APIs. 
3. In an event of an alteration made to the table or any of its databases, a basic change to only the XML file and related Java class would suffice. 
4. Only known Java files and data types will require to be worked on, there often is no need to work on the SQL data type. 
5. No application server is necessary for its effective functionality. 
6. With easy and simplified retrieval techniques, the complexity of the database is minimized. 
7. The data-access query used by Hibernate is highly simplified and easy to operate 

Web components can be defined as a conglomeration of different technological methods that permits the development of custom elements that are reusable with their enclosed feature functionalities made away from the remaining codes, which are subsequently used in web applications. 

The Web Components are helpful to developers in the context of reusing codes that are beneficial to their developing processes. This however is not as basic and easy as it may appear for the custom markups. For example, the complex HTML and its related patterns, may sometimes still need written custom UI controllers because overusing them recurrently can render a design messy.  

Web components aim to proffer solutions to such problems associated with reusing codes, using its major technologies which when combined, create a wide range of custom elements with enclosed functionality that can be recycled for reuse wherever applicable without the risk of code collision. 

The three main web component technologies are: 

Custom Elements 

These are a group of APIs in a JavaScript set that permits the expansion of custom elements and their patterns, which can be applied as recommended in the desired interface. 

Shadow Document Object Model (DOM) 

These are a group of JavaScript APIs used to combine an enclosed ‘shadow’ to an element that is separate from the main DOM, and in charge of related features. With this, elements feature privacy can be maintained, so they can be designed, scripted, and styled as pleased without colliding with other aspects of the documents. 

HTML Templates 

These are elements that assist the writing of markup templates that are not shown on the display page. These can be recycled repeatedly as the foundation of a customs elements’ structure. Such as <template> and <slots>. 

The Implementation Strategies For The Web Component: 

1. Design a class specifically for the web component features using its syntax  
2. Register the new custom element using the custom element registry. Indicate the name to be identified with, the specific class, and maybe the location where the element was retrieved from. 
3. Include a shadow DOM to the custom element if needed.  
4. Define the HTML template using the basic DOM and clone the template before attaching it to the shadow DOM 
5. Make use of the custom element in a similar way you would use any common HTML feature on the home page 

Object Relational Mapping (ORM) is a feature tool used to create and establish a link between a relational database and an object by generating a navigation plane between the object state and the column of the database. It can operate several databases such as updates, inserts, and delete feature functionalities. 

ORM serves as a bridge between Object-Directed Programs(ODP) and relational databases. 

While using different ODP languages, there is a need to create different operational performances such as creating - reading - updating - deletion (CRUD) data.

The ORM frameworks are: 

1. Hibernate 
2. ORMLite 
3. iBATIS 
4. TopLink 
5. JPOX 

The types of mapping include 

• Single-to-single 

Here, every feature in an entity is related to a particular feature in another entity. 

• Single-to-numerous 

In this entity, one particular feature can be related to multiple features in another entity. 

• Numerous-to-single 

Multiple features in an entity are related to a single feature in another entity. 

• Numerous-to-numerous 

Several features in an entity are related to multiple features in another entity. Here, either of the sides can represent the owning side. 

The functioning of the ORM within the J2EE framework is executed by setting up maps which are of two types, based on direction. 

Unidirectional mapping relationship 

Here, the relationship is such that only one party can make properties referral to the other. Only one side is established within this framework and empowered with the ability to make updates to the database system. 

Bidirectional mapping relationship 

In this relationship, two sides are involved, one is the owing side which is seen in the unidirectional relationship and acts similarly, and the other aspect is the inverse side, with this structure, every feature aspect possesses a relationship platform and can make a referral of entities or properties to the other. 

Hibernate is an interface existing between the Java app and the Hibernate framework. Several session methods are existing and are in use within the Hibernate framework such as the Save () and Update() methods.  

Save () Method  

Also called the Hibernate save is a feature that can be used to store entities in the database. This method is onboarded outside the confines of a transaction resulting in the storage of only primary entities.  

The save() method makes a TRANSIENT entity PERSISTENT by associating it with an org.hibernate.Session. 

Before the persistence of an entity, the save() method links a developed identifier to the identification field, after it is returned. Therefore, it must quickly execute the SQL statement to be inserted regardless of whether it is within or outside the transaction. This is because identifiers are created solely for the main entity, and this can result in inconsistency of data if there is a failure to flush the changes made or in cases where the application develops errors. 

Update () 

The update () method is a more simplified pattern that functions thus, 

1. It operates the SQL update queries for feature entities that are persistent. 
2. It discards transient objects lacking an identifier-associated entity. 

Just To Note: 

• For entries that are persistent, the save() method functions as an update() method and operates the update SQL queries. 
• For entries that are detached, an identifier already exists within such framework and the pattern of behavior of the save() method will be dependent on the identity generator when operating the insert query. 
• Applying both the Save () or Update () methods will provide both functions on the premise of identification fields that are available within the entity, and in most instances, it is preferred to use both as opposed to using just the save() or the update () methods. If the identifier is absent, the framework summons the save () entity, and if it is present, the update () entity is called. 
• Both the save () and update () entities can be utilized with both persisting and transient entities. In this case, the entities that persist will be acted upon by the update () method and get updated, while the transient entities will be inserted into the framework's database to be saved. 

One of the most frequently posed J2EE developer interview questions, be ready for this conceptual question.

The get() and load() methods are other Hibernate techniques used to retrieve data from a database. At a glance, both of these methods may look similar but are innately distinct from each other. 

The get() method retrieves an object by deriving it from the cached Hibernate database while the load() method retrieves data by returning the reference of a hypothetical object that may not be in existence, it loads the data either from a database or a cache after accessing other objects properties. 

The use of get() in retrieving non-existing data would automatically redirect it to null, this is because it attempts to load the data immediately after it is called up. This is different with the load() method, here, it is possible to print the ID, however, just after attempting to access other fields, a database query is fired and yields org.Hibernate.objectnotfoundexception. This happens when there is no record located in that particular identifier because it is specific to the Hibernate runtime exception, therefore, there is no need to catch it directly. 

To reiterate the differences between the get() and load() methods; 

• The data is loaded by get() at the instant it is called upon while load() sends a proxy object and loads the data at instances when it is specifically needed. 
• The Load() method facilitates sluggish loading, which makes it a better method. 
• The load() method throws an exception when the sought data is unavailable, therefore, it can be utilized when there is the certainty of the existence of data in the database 
• Get(0) can be used to ensure the presence of sought data in the database. 

By sharing issues and helpful solutions, design patterns in programming enable you to take advantage of the collective knowledge of the developer community. The definition and context of an issue, a potential solution, and the results of that solution must all be included in a design pattern.

Design patterns can be divided into two groups for the sake of J2EE application architecture: those that address general software development concerns and those that focus on J2EE -specific issues.

The bare minimum of known issues that a sound application architecture should address is identified by J2EE specific design patterns. When it comes to directing the creation of architecture, the first category, which includes software development patterns that aren’t J2EE specific, performs just as well.  

A staple in J2EE design patterns interview questions and answers, be prepared to answer this one using your hands-on experience. Here is the answer -

There are three categories of design patterns in J2EE, each with various subcategories:

Presentation Layers Design Pattern: 

1. Intercepting Filter Pattern: A request and response can be intercepted and altered both before and after the request is complete with an intercepting filter pattern. It is used when a user needs centralization, and common processing across requests, including recording details about each request, compressing an outgoing answer, or examining the data encoding method of each request. 
2. Front Controller Pattern: In a scenario where a user wants to create a centralized request handling method so that all requests are handled by a single handler, the front controller pattern is best suited for this. This handler can handle requests’ authentication, authorization, logging, and tracking before forwarding them to the appropriate handlers. 
3. View Helper Pattern: The processing of the data for the business model is separated from the static view, such as a JSP.
4. Composite View Pattern: Building composite views from several subviews is the responsibility of the composite view pattern. The composite view pattern enables the framework to be linked to both the content and the layout. This greatly streamlines the application’s development process.

Business Layer Design Pattern: 

1. Business Delegate Pattern: The business delegate hides the actual implementation of the business services and serves as a client-side business abstraction. It lessens the connectivity between the system’s business services and presentation-tier customers. 
2. Service Locator Pattern: It is a design pattern used in software development to tightly group the steps necessary to acquire a service under a robust abstraction layer. This design makes use of a central register called the “service locator,” which, in response to a request, returns the data required to carry out a certain operation. When service clients or service consumers request specific instances of a service, the ServiceLocator is in charge of providing those instances.
3. Session Façade Pattern: The creation of enterprise apps is the primary use of the Session Façade design. The pattern captures the interaction that takes place between the low-level components. It is implemented as a Session EJB, a higher-level component. Then, in order for the app or a component of the app to work, it must have a single, standard interface.
4. Transfer Object Pattern: When a user wishes to send data with various attributes all at once from the client to the server, the transfer object pattern is used. The Transfer Object Pattern is a straightforward POJO class with getter and setter methods that are serialized to enable network transfer 

Integration Layer Design Pattern: 

1. Data Access Object Pattern: The DAO pattern is used to differentiate between high-level business services and low-level data accessing APIs or actions.
2. Web Service Broker Pattern: XML and web protocols are both used by the web service broker. This pattern can be used to expose and broker the services. It serves as a general gateway or addresses that the client apps can use to access a wide range of services.

JTable class is a component of the Java Swing Package, the JTable class is typically used to show or update two-dimensional data that has both rows and columns. It’s a lot like a spreadsheet. This creates a table with data arrangement.

JTable Constructors: 

1. JTable() creates a table with blank cells.
2. JTable(int rows, int columns) creates a table with the dimensions or rows * columns. 
3. JTable(Object[][] data, Object []Column) creates a table with the supplied name, and []Column specifies the names of the columns in the table.

Features of JTable: 

1. addColumn(TableColumn []column) adds a column to the end of the JTable. 
2. clearSelection() selects each row and column that have been chosen. 
3. editCellAt(int row, int col) edits the specified indices if they are valid and the corresponding cell is editable.
4. setValueAt(Object value, int row, int col) sets the cell value as “value” for the location row, col in the JTable.

Below is an example of a Java JTable: 

import Javax.swing.*;
public class TableExample {
JFrame f;
TableExample(){
f=new JFrame();
String data[][]={ {"101","Amit","670000"},
{"102","Jai","780000"},
{"101","Sachin","700000"}};
String column[]={"ID","NAME","SALARY"};
JTable jt=new JTable(data,column);
jt.setBounds(30,40,200,300);
JScrollPane sp=new JScrollPane(jt);
f.add(sp);
f.setSize(300,400);
f.setVisible(true);
}
public static void main(String[] args) {
new TableExample();
}
}

Output: 

The two patterns are the Proxy Pattern and the Chain of Responsibility.  

The Proxy Pattern enables users to build a middleman that serves as an interface to another resource while simultaneously masking the component’s inherent complexity. When using a Proxy pattern, there is an assured response to the request if the communication between the client and server locations is functional.  

The Chain of Responsibility pattern processes a request from the client sent to a chain of objects, which is used to establish loose coupling in software design. Later, each object in the chain will choose for itself who will handle the request and whether or not it has to be forwarded to the following object in the chain. The response is not certain in the case of the Chain of Responsibility. It implies that even if the request makes it all the way to the top of the chain, it might not be handled.

One of the fundamental Java EE design patterns is the business delegate pattern. It is utilized to disconnect or lessen the link between the business services and the presentation tier. Additionally, the lookup function in the business layer code contained within the presentation tier code must be removed in order to hide the implementation details of the services.  

The business delegates frequently take on the role of adapters in order to invoke the business objects that are present in the presentation tier. The business delegate pattern is set up so that a client sends a request and establishes a connection with a business delegate object that utilizes a business service. The business service that the business delegated access to is created by the lookup service.

A staple in J2EE design patterns interview questions and answers, be prepared to answer this one using your hands-on experience.

Communication between items is demonstrated through behavioral patterns. The designer can concentrate on how objects communicate thanks to behavioral patterns. Examples of behavioral patterns include command, chain of responsibility, memento, template method, state, observer, interpreter, strategy, and visitor.

a.  Command: The objects include a function and all required input and output parameters. The objects that will initiate the action and the objects that perform the action are kept apart when various actions are carried out by triggering these items from the outside. The objects can be used in a variety of operations and can be kept in collections. When additional functionality is required, adding new command objects is also a simple process

b. Chain of Responsibility: A group of function classes and the command classes necessary to initialize those classes make up this design pattern. Function classes record the type of work they perform and choose the function class that will be the next in the array. When a process needs to perform a given number of functions sequentially, this design pattern might be employed. 

c. Memento: An object can maintain its state and then reset to the state it was in before the most recent action was taken thanks to this design pattern. In other words, it offers a mechanism to hide some of the object’s states and return to them when needed.

d. Template Method: In the hierarchy of classes, the template method is the top class. This top class reveals the model that subclasses should adhere to; the details are left up to the subclasses. This design technique prevents code redundancy in lower classes. In the higher class, the common codes of the lower classes are gathered in one location. This is done at some point when a change to this shared part is required.

e. State: If an object’s behavior changes as its state changes, the State design pattern may be employed. Using this design pattern removes the cumbersome “if/else” or “switch” statements from controlling the diverse behaviors of objects depending on their state if we have objects that respond differently in different circumstances.

f. Observer: When an object’s state changes and we wish to notify other objects of those changes, we utilize this design pattern. In other words, a large number of objects that are in the position of listeners continuously monitor an object’s state, and these observers are alerted when something changes.

g. Interpreter: This design pattern’s goal is to translate a specialized computer language. The main concept is to split each sign of this specialized language into its own class. In database management systems, this design pattern can be used to parse languages similar to SQL.

h. Strategy: The object decides which method to use when several are appropriate for a given task. The specifics of how the method should be used are isolated from the object that will use with the help of this design pattern. Additionally, the code is removed from the lengthy “if/else” or “switch” lines while utilizing this design pattern.

i. Visitor: This design pattern can be applied to a wide variety of objects. The items remain unchanged. Visitor objects carry out the action. This design pattern can be applied when the system does not introduce new objects but constantly requires the addition of new operations. The action-related codes are grouped into one main object

1. Intercepting filter pattern: Intercepting Filter applies a filter to both incoming requests and outgoing answers. These filters can be added and deleted declaratively, making it possible for them to be used in several combinations without being overtly noticeable. The final filter in the group vectors controls the initial target object after the preprocessing and/or postprocessing is finished. This is frequently a Front Controller for an incoming request, although it could also be a View.
2. Composite view pattern: Composite View refers to creating a View out of multiple atomic components. To build a single template, various smaller static and dynamic views are combined. A frequent fusion of other patterns from the catalog is shown by the Service to Worker and Dispatcher View patterns. The two patterns both have a controller that collaborates with a dispatcher, views, and helpers as part of their shared structure. Dispatcher View and Service-to-Worker have comparable participant responsibilities, but they differ in how those roles are split up. Dispatcher View, in contrast to Service to Worker, delays business processing until after view processing has been completed.  
3. Front controller pattern: The presentation tier’s common processing logic, which may otherwise be mistakenly placed in a View, is included in the Front Controller. A controller manages navigation, security, content retrieval, and view management while outsourcing dispatching to a View to a Dispatcher component.  
4. Application controller pattern: The processing of views and commands is centrally controlled, retrieved, and invoked by the application controller. The Application Controller Pattern is in charge of locating and calling commands, as well as locating and dispatching to views, whereas a Front Controller serves as a centralized access point and controller for receiving requests.
5. Context object pattern: Context Objects allow you to communicate state throughout your whole application in a manner that is protocol-independent. Testing is made simpler by using context objects, which allows for a more generic test environment with less reliance on a particular container.
6. View Helper Pattern: The separation of formatting-related code from other business logic is encouraged by View Helper. It advises encapsulating the functionality for starting content retrieval, performing validation, and modifying and formatting the model in Helper components. The presentation formatting is subsequently put into the View component. A View may be made up of several subcomponents to construct its template, in contrast to Helper components, which commonly delegate to the business services through a Business Delegate or an Application service.
7. Dispatcher view pattern: To manage client requests and create a dynamic display as the response, Dispatcher View integrates a controller, dispatcher, views, and helpers. Since content retrieval is a task that is delayed until after view processing, controllers do not assign it to helpers. A dispatcher, which can be contained within a controller, a view, or another component, is in charge of view management and navigation.
8. Service to worker pattern: Before control is sent to the view, the service to worker handles basic request handling and invokes business logic. Before handing control over to the view, it centralizes control and request handling to retrieve a presentation model. A dynamic response is produced by the view depending on the presentation model.

• Application service pattern: Application Services give a standard service layer to the business titer services by centralizing and aggregating behavior. Other services or business objects may interact with an application service. A layer of services can be added to your application by using an application service to call another application service.
• Business delegate pattern: Business delegate offers a point of entry for using remote services in the business layer and lessens connection across remote tiers. To enhance performance, a business delegate may also cache data as required. A Business Delegate maintains a one-to-one relationship with a Session Façade by encasing it. A Session Façade is triggered by an Application Service using a Business Delegate.
• Service locator pattern: The implementation strategies for locating business service components are encapsulated by Service Locator. A Service Locator is used by a Business Delegate to connect to a Session Façade. A service locator can be used by other clients who need to find and connect to Session Façade, other business-tier services, and web services.
• Session façade pattern: By masking the complexity of the interactions between business services, Session Façade offers coarse-grained services to the clients. Numerous Application Service implementations or Business Objects may be called by a Session Façade. A Value List Handler may also be contained within a Session Façade.
• Transfer object pattern: By reducing the number of calls necessary to obtain data from another tier, the Transfer Object Pattern offers the finest methods and approaches for exchanging data across tiers (i.e., across system boundaries) and so lowering network overhead.
• Business object pattern: The conceptual domain model is put into practice by Business Object using an object model. Business objects divide your application’s business data and logic into independent layers. Business objects often stand in for permanent items, and Domain Store enables transparent persistence.
• Value list handler pattern: The GoF iterator design is used by the Value List Handler to provide query execution and processing services. The Value List Handler stores the results of query execution in a cache and provides clients with requested subsets of the results. It is possible to avoid the costs involved with locating numerous entity beans by employing this strategy. The Value List Handler runs a query and retrieves the results from the persistent store using a Data Access Object. 
• Composite entity pattern: Using local entity beans and POJOs, Composite Entity implements a business object. A Composite Entity employs Data Access Objects to aid persistence when it is implemented using bean-managed persistence.  
• Transfer object assembler pattern: From several sources, the Transfer Object Assembler creates a composite Transfer Object. These sources could be Data Access Objects, EJB components, or any other Java object at random. The best time to apply this pattern is when the client needs to get data for the entire model or a specific component of the model.

• Service Activator Pattern: Corporate applications can use JMS to provide asynchronous processing thanks to Service Activator. An Application Service, Session Façade, or Business Objects can all be called by a Service Activator. To offer parallel asynchronous processing for lengthy operations, you can also use multiple Service Activators.
• Domain Store Pattern: A potent tool for implementing transparent persistence for your object model is provided by Domain Store Pattern. Data Access Objects are one of the many other patterns it mixes and connects.
• Web Service Broker Pattern: Using XML and common web protocols, Web Service Broker exposes and brokers one or more services from your application to external clients as a web service. Application Service and Session Façade can communicate with a Web Service Broker. A Web Service Broker processes a request asynchronously using one or more Service Activators.
• Data Access Object Pattern: Loose coupling between the resource and business levels is made possible by Data Access Objects. The whole data access logic required to create, access, remove, and update data from persistent storage is included in a data access object. Transfer Object is used by Data Access Object to send and receive data.

• MVC Pattern: A data model, presentation information, and control information must all be included in an application, according to the Model View Controller (MVC) design pattern. Each of them needs to be divided into separate items to follow the pattern.  
• Business Delegate Pattern: The Business Delegate serves as a client-side business abstraction, hiding the actual implementation of the business services by providing an abstraction for them. It lessens the connectivity between the system’s Business services and presentation-tier customers.
• Composite Entity Pattern: EJB persistence technique uses the Composite Entity pattern. An EJB entity bean called a composite entity serves to represent a graph of an object. Internally dependent object beans are automatically updated when a composite entity is updated since they are handled by an EJB entity bean 
• Data Access Object Pattern: Low-level data accessing APIs or operations are separated from high-level business services using the Data Access Object Pattern.
• Front Controller Pattern: According to the front controller design pattern, each request for a resource in an application will first be handled by one handler before being forwarded to the handler who is most suited to handle that particular sort of request. Other helpers may be employed by the front controller to complete the dispatching mechanism. 
• Intercepting Filter Pattern: Having a straightforward system for adding and removing processing components, where each component completes a particular filtering function, is the key to tackling this challenge flexibly and unobtrusively.  
• Service Locator Pattern: The service locator pattern is a design pattern used in software development to tightly abstract the steps necessary to access a service. This design makes use of a central register called the Service Locator, which, in response to a request, returns the data required to carry out a certain operation. 
• Transfer Object Pattern: Transfer Object Pattern may include all of the data from a source or only a portion of the data. They can store information from a single source or several. When used, DTOs take over as the method for transferring data across systems. 

A staple in J2EE advanced interview questions and answers, be prepared to answer this one using your hands-on experience.

The Web container in J2EE is a holder for web applications in the J2EE framework. The primary responsibility of the web container is to establish the operational environment for web applications, it extends the server functionality features by availing developers of a conducive environment to operate servlets and JavaServer Pages (JSPs).

The servlets create a component platform that is self-enabling for building web-based apps. The web applications are a combination of servlets, pages of HTML, class groups, and other features that combine to form a complete app in the J2EE . 

The web container also grants web-apps access to local EJBs which are resident within the naming directory of Java. 

The login control of the web container for web applications can be controlled by establishing different log levels, this controls the kind of data that will be logged. To establish log levels for a web container, the following operations can be performed:

1. Find the web container application to be operated on in the J2EE interface 
2. Expand the tab for the container 
3. Select the web container from the numbered list of J2EE containers that are outlined 
4. The page will get displayed on the logging-in web container in the administration interface of the application. 
5. Choose the preferred log level from the drop-down  
6. Complete this task by clicking on the save bar. 
7. If there is a need to generate more features for the web container, the properties button in the application interface can be used. 

Connection pooling is the collection of a cache of database links that are preserved to enable the recycling and reuse of connections by developers when a subsequent request for that database is made. Connection pools serve as performance-enhancing tools used in the operation of a database and its commands.

The normal expansion and maintenance of a database connection for every user, especially for those made for a changing database application, is daunting, cumbersome, and resource-wasting. But in connection pooling, a connection is kept in a pool for reuse after it has been developed, this eliminates the need for creating a new connection.

If all the connections are in use, a separate connection is created and added to the connection pool. The use of this concept also serves to minimize the amount of time a developer would spend on creating a connection and the time a user will spend waiting for the database connection to be established. 

Spring framework is also simply referred to as just “Spring”. It is a framework of an open-source application that makes technical resources available for the support of Java applications that are being built such as the J2EE application framework. It also assists in the development of high-performance applications using certain Java objects like the plain old Java object (POJOs). 

Spring is seen as a low-cost source framework that still maintains app security and flexibility. It enhances the coding techniques and minimizes the general app-generation time due to its lightness. It is effective at making use of system resources and requires a lot of support. 

The spring framework works in the following ways: 

It utilizes a web application architectural framework that is organized into three layers, each of which is interdependent for the proper functioning of the application.

Display or View Layer 

It acts as a UI and is the most outer layer of the architecture responsible for presenting the contents and user interactions.

Enterprise Logic Layer 

It is the middle or central layer responsible for the program's logic. 

Data Access Layer 

This is the deepest and innermost layer of the framework responsible for the retrieval of data from their sources. 

Since these layers are dependent on themselves. There is a free flow of communication among them. Therefore, the function within the confines of “dependency” and a basic application will possess numerous classes in thousands and several dependencies.  

The benefits of the spring framework are: 

• Pre-designed templates 

There are pre-made templates contained in spring such as the templates for Hibernate which alleviates the stress on developers to create complex and cumbersome codes. 

• Simplified tests 

The presence of the dependency addition techniques makes the spring application be considered freely coupled and this makes the application easier to test in a framework. The server is needed by the EJB and Struts applications to operate the app. 

• Rapid design 

The design creation process is fast due to the assistance of the dependencies, making it easier to incorporate the frameworks and aid the build-up of the J2EE apps. 

• Powerful abstraction 

The Spring framework accommodates powerful abstractions for the J2EE apps such as the JPAs.  

• Properly organized framework 

Spring is an MVC platform that delivers good web framework options for the creation of applications with the help of struts or other app frameworks. 

• Light weighted 

In comparison to other EJBs, the spring framework is lightweight and this aids the deployment of apps on systems with a limited memory and processing unit. 

• Frequent management of transactions 

Spring establishes scaled platforms that encourage local transactions such as in the use of one database to execute up-scaled international transactions. 

Application Client Module: The application client is a standalone Java program that executes on the client machine inside of a JVM that is supported. To carry out activities like system or application administration. When utilizing the J2EE business tier capabilities, they provide an interface that is comparable to the ones already present on the native client. While interacting with a servlet, it can also establish an HTTP connection.  

Advantages: 

Both web browsers and application containers are capable of hosting an application client. 

It can access all J2EE services because it has the appropriate libraries.  

Web Module: A server-side entity called a web component can reply to HTTP queries. They are used by browsers and other web-based clients to communicate with J2EE applications. They include filters, web event listeners, Java servlets, and JSP pages. JSP pages are used to produce dynamic web pages and server-independent web-based applications, whereas Java servlets are used to handle requests and build responses. The construction of a web component involves the following four steps: 

• Writing code for web components.  
• Placing the web component and its resources in a package. 
• Installing an application container web component. 
• Accessing the web component’s link.  

Enterprise JavaBeans Module: The Java API known as Enterprise JavaBeans (EJB) is used for the common development of enterprise software. They are server-side software elements that summarize and encapsulate an enterprise application’s business logic. A runtime domain for web-related software services such as computer dependability, Java Servlet Lifecycle (JSL) management, and the transaction process is generated by the Enterprise JavaBeans web repository. 

The server-side business software that is typically found in enterprise applications can be easily implemented using the EJB enumeration, a subset of the Java EE enumeration. Lifecycle management, security, object pooling, and transaction management are among their responsibilities. The specification divides Enterprise JavaBeans into three categories:  

• Session Beans: Business logic for the application is included in session beans, which can be requested by local, remote, or service clients.  
• Entity Beans: They are a contained representation of business objects that are made accessible through a persistent method. 
• Message-Driven Beans: They contain business logic that may be requested by passing messages, just like session beans do.  

Resource Adapter Module: A resource adapter is a system-level software driver that, when a resource adapter for the particular Enterprise Information System (EIS) is delivered to the server, enables J2EE components to interface with a backend EIS through a JCA-compliant application server. J2EE components and applications built with J2EE components can execute business functions through the Resource Adapter, as it’s fully compliant with the Java Platform and should work with any application server that is J2EE certified.

• By implementing Action Interface: The action interface defines one no-argument method and five constants which are Success, None, Error, Input, and Login.  

public interface Action { 
public static final String SUCCESS = "success"; 
public static final String NONE = "none"; 
public static final String ERROR = "error"; 
public static final String INPUT = "input"; 
public static final String LOGIN = "login"; 
public String execute() throws Exception; 
} 

An example of the LOGIN action class: 

<!DOCTYPE struts PUBLIC 
"-//Apache Software Foundation//DTD Struts Configuration 2.0//EN" 
"http://struts.apache.org/dtds/struts-2.0.dtd"> 
 <struts> 
  <package name="user" extends="struts-default"> 
   <action name="Login" class="com.w3spoint.action.Login"> 
  <result name="success">/welcome.jsp</result> 
  <result name="error">/login.jsp</result> 
   </action> 
  </package> 
 </struts> 

Output:

Enter Username and Password:

Click on Login:

• Using Struts2 @Action annotation: The URL pattern for an Action class is defined by the @Action annotation in Struts2. The methods of an action class can each be retrieved using a different URL. The ability to hide the package name in the URL is provided by this feature. 

@Result(name="success",location="/user/user.jsp") 
public class UserAction extends ActionSupport{ 
private static final long serialVersionUID = 1L; 
@Action("/url/one") 
public String one() { 
    return SUCCESS; 
} 
} 

• Extending ActionSupport Class: A number of interfaces, including Action, Validatable, Serializable, and LocaleProvider, are implemented by the ActionSupport class. The action interface is less frequently utilized than the ActionSupport Class.

Any regular Java class that has an execute() method that returns a String can be set up as an action class. 

A staple in J2EE design patterns interview questions and answers, be prepared to answer this one using your hands-on experience.

An interface called externalization lets users create unique guidelines and their own serialization process. Serialization is a method for writing an object’s state into a byte stream. Java serialization isn’t particularly effective to serialize bloated objects that have numerous characteristics and properties, and in cases like these, externalization would be more effective.

For instance, it is possible to externalize the Serialization interface after implementing it in a class using the writeExternal() function. The readExternal() method will be used to generate an instance of the object when users reconstruct an externalized object on their end. Thus, serialization is made available through externalization, making it easy to control object steam and choose what to store there.

In a scenario where only a portion of an object needs to be serialized, externalization is very helpful as only the object’s required fields would be serialized.

There are four development roles in the J2EE Application:

• Presentation Content Developer: Today, one of the issues with most internet application development efforts is that the focus is too much on creating the business logic itself and not enough on creating an appealing and aesthetically pleasing user interface. The outcome is a refusal to utilize the program or just switching to another approach to get the same outcome. These quick yet unsatisfactory contacts can have a long-lasting impact on an organization’s productivity and effectiveness.

Organizations are starting to understand that an application’s actual usability – including its ergonomics and GUI aesthetics – is a crucial component of its success. The majority of Java developers should be able to fully educate themselves in order to give any development value as the intricacy of Web GUI development and the quality of GUI interface needed by business application customers both reach new heights.

To design and implement the J2EE application interface, organizations must work with experts in the fields of art, ergonomics, mass communication, and creative content.

• Web Component Developer: A J2EE compliant web server’s architecture requires that a Web Component Developer create the presentation logic necessary to support a web-based J2EE client interface. A web component developer should ideally have experience creating JavaServer Pages, Servlets, Web-based applets, and other Web-related technologies like HTML and XML
• Business Component Developer: The ability to translate business needs into business logic, which is implemented on the J2EE platform as Enterprise JavaBeans, is the key competency required of business component developers. They should have technical knowledge of the J2EE platform architecture and how it can connect with the EIS tier, as well as knowledge of the business domain they are building for. 
• EIS Integrators: Occasionally, a J2EE project needs to integrate heavily with numerous EIS layer systems that are not Java-based, or perhaps the technologies are more proprietary in nature. In such cases, the design, development, and implementation of the communication pipeline between the J2EE platform and the particular enterprise information system will require the involvement of an EIS integration specialist.

J2EE 1.4 is an enhanced version of J2EE 1.3. It is the most complete web services platform ever.  

J2EE 1.4 includes: 

1. Java API for XML-Based RPC (JAX_RPC 1.1) 
2. SOAP with Attachments API for Java (SAAJ) 
3. Web services for J2EE (JSR 921) 
4. J2EE Management Model (1.0) 
5. J2EE Deployment API (1.1) 
6. Java Management Extensions (JMX) 
7. Java Authorization Contract for Containers (JavaACC) 
8. Java API for XML Registries (JAXR) 
9. Servlet 2.4 
10. JSP 2.0 
11. EJB 2.1 
12. JMS 1.1  
13. J2EE Connector 1.5  

The new JAX-RPC 1.1 API, which allows service endpoints based on Servlets and enterprise beans, is a feature of the J2EE 1.4 that offers whole support for web services. Interoperability with Web services built on the WSDL and SOAP protocols is offered by JAX-RPC 1.1.  

The web services for the J2EE standard (JSR 921), which specifies Web service deployment criteria and makes use of the JAX-RPC programming style, is also supported by the J2EE 1.4 platform. The WS-I Basic Profile 1.0 is supported by the J2EE 1.4 platform in addition to a large number of web service APIs. This indicates that J2EE 1.4 enables platform Web services interoperability in addition to platform freedom and full Web services capability.  

The J2EE Management 1.0 API, which provides the information model for J2EE management and includes the common Management EJB (MEJB), is also introduced by the J2EE 1.4 platform. The Java Management Extensions API (JMX) is utilized by the J2EE Management 1.0 API. The J2EE Deployment 1.1 API, which offers a standard API for deploying J2EE applications, is another addition to the J2EE 1.4 platform. 

The Java Authorization Contract for Containers (JavaACC) was added to part of the J2EE 1.4 platform to improve security. By establishing a uniform method for integrating authentication systems into J2EE containers, the JavaACC API enhances security.  

Thanks to improvements made to the Java Servlet and JavaServer Pages (JSP) technologies, the J2EE platform now makes it simpler to design web front ends. Request listeners and improved filters are now supported by servlets.  

With the advent of a basic expression language, tag files, and a more straightforward tag extension API, among other things, JSP technology has simplified the page and extension development models. This makes it simpler than ever for developers, especially those who are comfortable with scripting languages, to create JSP-enabled pages. 

The web client is a crucial component, and it also has the following two components that describe how it works: 

1. Dynamic portion: This provides dynamic web pages utilizing a variety of markup languages, including HTML, XML, and others. This portion is produced by the web components that are active in the web tier. The pages can only be rendered by a web browser. 
2. Static portion: This delivers static pages to the client from the server that don’t change in response to requests. It provides information that is static and always static, such as support information or information about us. 

The web client is referred to as a “thin client,” which is a very basic web-based client that doesn’t do any queries, business rule execution, or application connection. It offers efficient operations and gives the server’s applications protection, speed, and a variety of services.

The applet is a type of application client that runs on the client side and gives the user a way to manage the task that enables them to use the interface. A graphic user interface is offered, and assistance tools are available. Swing and the advanced window toolkit are used in the command line interface to build the graphical user interface.

The applets were created in Java. This is installed on the web browser and executed on the virtual machine that Java uses. The plug-in is necessary for the client system’s use of security policy, which correctly executes the program in the web browser. The components build web client programs and execute the application on the client side using API keys. The files are not required on the client system because no security is permitted. It offers an application design utilizing applets that is more modular.

The Servlet and JavaBeans component architecture is used by the application client to communicate over the HTTP connection. The application client also comprises a number of components to control the overall data flow for the server and the client’s communication needs.

This, along with other interview questions on J2EE for freshers, is a regular feature in J2EE interviews, be ready to tackle it with the approach mentioned below.

An application client is a program that runs on the client side and gives the user a way to manage the task that enables them to use the interface. A graphical user interface is offered, and assistance tools are available. Swing and the advanced window toolkit are used in the command line interface to build the graphical user interface. 

Due to the application being managed at the business tier, these clients can use them immediately. The servlet and JavaBeans component architecture is used by the application client to communicate over the HTTP connection. The application client also comprises a number of components to control the overall data flow for the server and the client’s communication needs. 

Instance variables can be used with an object by using JavaBeans components. Instance variables are used on the server side to obtain data from the user and set it on the server using get and set methods. It offers a wide range of options and components that can be used for the client tier. The business logic that the server provides to execute the applications is how the client and server communicate.  
 
By browsing the pages that are being created and transferring data from the web layer, the web browser is used to communicate through the server. The J2EE application employs a thin client or thick client that offers the client both light and heavy capabilities while minimizing server load.

A component and the low-level, platform-specific functionality that enables it are connected through containers. A web component, enterprise bean, or application client component must be put together into a J2EE module and deployed into its container before it can be performed.  
 
The J2EE application itself, as well as each component, must have container settings specified as part of the assembly process. The J2EE server’s foundational support, including features like security, transaction management, Java Naming and Directory Interface Trademarked (JNDI) lookups, and remote connectivity, can be tailored using container settings. Some of the highlights are as follows:  

Only authorized users are able to access system resources when a web component or enterprise bean is configured using the J2EE security paradigm. 

To ensure that every method in a transaction is regarded as a separate unit, the J2EE transaction model allows you to declare relationships between the methods that make up a single transaction.  
For application components to access naming and directory services, JNDI lookup services offer a uniform interface to several name and directory services throughout the company.

Enterprise beans and clients’ low-level communications are handled via the J2EE remote connectivity concept. A client can call methods on an enterprise bean after it has been built as though it were located in the same virtual machine.

Due to the flexible services offered by the J2EE architecture, application components inside a single J2EE application can act differently depending on where they are deployed. For instance, an enterprise bean may have security settings that permit it to access database information at one level in a production environment and at a different level in a different production environment.

The container also controls access to the J2EE platform APIs as well as non-configurable services such as database connection resource pooling, data persistence, enterprise bean and servlet life cycles, and access to the J2EE platform APIs.

Although data persistence is a non-configurable service, the J2EE architecture allows you to override container-managed persistence by incorporating the necessary code in your enterprise bean implementation when you need more control than the default container-managed persistence. 

The Enterprise Bean Developer platform utilizes numerous services for various components, and it is always necessary to specify the task, such as:  

The JAR file, utilized by Java itself, is a crucial file that contains all the archived files. It is utilized for the subsequent tasks: 

• The source code needs to be correctly written and compiled. 
• The program that needs to start is specified using the deployment descriptor. 
• A bundle is created by combining class files with the .class file extension so that it may be utilized as a single file. The descriptor must be present in the JAR file for it to work.  

The J2EE API enables the integration of the offered components by the system and applications. It makes this possible in the following ways and manners: 

1. All levels of the enterprise bean incorporate the application used using the API. The unified application model is utilized in this. 
2. The request and response are presented in a more straightforward way by the J2EE API. This method makes it possible for the JSP page and servlet to be easily represented so that they may be implemented on the server. 
3. It adheres to the JAAS-based reliable security model and makes it possible to employ the security mechanism across the board for all application models. 
4. It enables simple API integration utilizing JAXP, an XML-based data transfer architecture that has been created to give the new attributes and manage them from a single location.       
5. It employs the J2EE connection architecture in a more straightforward way and offers compatibility between the connector. 
6. Using the JDBC APIs, enables database connectivity across numerous database systems.