Oracle (Sun Microsystems) first introduced the J2EE (Java Enterprise Edition) standards to assist developers in creating, deploying, and maintaining enterprise-level commercial applications that are reusable, distributed, trustworthy, scalable, portable, and secure. J2EE, which stands for Java 2 Enterprise Edition, is a set of frameworks, an assortment of APIs, and numerous J2EE technologies (JSP, Servlets, etc.) that are used as standards for streamlining the creation of large-scale applications.

It aims to make the process of creating, building, and deploying enterprise-level applications that can operate on various platforms that accept Java easier. Because J2EE is still the most widely used standard among Java developers, it's critical for developers to be familiar with and skilled in J2EE ideas. In this article we have shortlisted the most commonly asked interview questions on J2EE for both experienced and freshers.

Top J2EE Interview Questions for Freshers and Experienced Professionals

1. What is J2EE?

J2EE, or Java Enterprise Edition, is a Java-based platform that combines services protocols with APIs (Application Programming Interfaces), giving users the ability to create enterprise-level applications that are multi-tiered, safe, stable, and quick. J2EE offers a variety of specifications for creating enterprise-level online applications, including web, enterprise, web service, and others.

2. What are the benefits of J2EE?

Given below are the benefits of J2EE:

  • Faster time to market: J2EE employs the idea of containers to make development simpler. This supports the separation of business logic from lifecycle management and resources, allowing developers to concentrate more on the business logic than the infrastructure. The EJB (Enterprise JavaBeans) container, for example, handles threading, distributed communication, transaction management, scaling, etc. and offers the developers the necessary abstraction.
  • Support for Web Series: A platform for creating and deploying web services is offered by J2EE. The Java API for XML-based Remote Procedure Call, or JAX-RPC, assists programmers in creating SOAP-based web services, clients, and endpoints that are portable and interoperable.
  • Compatibility: The "Write Once, Run Anywhere" guiding philosophy is used by the J2EE platform. It offers thorough standards and APIs that guarantee interoperability between various application providers and, as a result, the portability of programmes.
  • Simplified Connectivity: J2EE facilitates applications' connectivity, enabling the use of various devices' capabilities. Additionally, it offers JMS (Java Message Service) for asynchronous, loosely linked application integration. Additionally, it offers support for CORBA (Common Object Request Broker Architecture), which enables close system integration through remote calls.

3. Name various components of J2EE application architecture.

J2EE is made up of 3 main components (tiers) - Client tier, Middle tier, Enterprise data tier:

  • Client Tier: Programs and apps in this tier typically run on machines other than the server and interact with users. Different user inputs are taken in this instance, and the requests are submitted to the server for processing before being returned to the client with the result.
  • Middle Tier: Web components and EJB containers make up this tier. The web components that process the request and produce the response are either servlet or JSP pages. Static HTML codes, programmes, and applets from the client are packed with the server's components when the application is put together, along with the web components. The Enterprise Bean, which is running on the business tier, needs the EJB components to handle input from the user.
  • Enterprise Data Tier: Database servers, resource management programmes, and several other data sources are included in this tier and are accessible by various business tier components via a separate workstation. This tier makes use of technologies like JPA, JDBC, Java transaction API, Java Connector Architecture, etc.

4. What are the different technologies provided to the J2EE platform?

Given below are the important technologies provided to J2EE platform:

  • Java Server Pages (JSP): Delivering XML and HTML documents makes use of this. In addition to these, we may use other sorts of data using OutputStream.
  • Java API for XML Based RPC (JAX-RPC): This is used to create web applications and clients that employ Remote Procedure Calls and XML.
  • Java Servlets: The request-response approach can be used to access applications hosted by servers, which are extended by classes known as servlets.
  • Enterprise Java Beans: This is a server-side component that provides runtime environment, security, servlet lifecycle management, transaction management, and other services in order to encapsulate the business logic of the application.
  • J2EE Deployment API: It offers specifications for web services deployment.
  • J2EE Connector Architecture: This establishes a common framework for linking J2EE platforms with other EIS (Enterprise Information Systems), including mainframe operations, database systems, and many legacy applications written in other languages.
  • J2EE Authorization Contract for Containers: This is used to specify security agreements between application servers and authorization policy modules.
  • Java Management Extensions (JMX): They are used to provide tools for managing and monitoring networks, objects, devices, and applications.
  • Java API for XML Registries: This gives users a consistent API to access several XML Registries, enabling the infrastructure needed to create and deploy web services.
  • Java Message Service (JMS): This messaging standard enables distributed, loosely coupled, asynchronous, and reliable communication across various J2EE components so that they can create, send, receive, and read messages.
  • Java Transaction API (JTA): This is used to specify the Java standard interfaces for managers and transaction systems.
  • Java Naming and Directory Interface (JNDI): For Java-based applications, this API offers name and directory functionality.
  • JDBC Data Access API: This offers APIs for obtaining data from several data sources, including relational databases, flat files, and spreadsheets.
  • Common Object Request Broker Architecture (CORBA): In order to facilitate system communication implemented on many platforms, this standard for establishing Object Management Groups is provided.

5. How is JDK different from JIT?

A cross-platform software development environment called JDK (Java Development Kit) provides diverse collections of libraries and tools needed to create Java programmes and applets. It also includes JRE, which offers tools and libraries that support the execution of byte code. JDK is required for creating and executing Java programmes. while JIT refers to the Just In Time Compiler, a module found inside the JVM (which is inside JRE). For the purpose of reducing compilation time and improving speed, JIT compilers are used to compile some portions of byte code that perform similarly to machine code simultaneously.

6. What do you understand by build file?

A build file is used to automate numerous software development processes. The build file additionally specifies the versions of libraries that must be included in addition to this. The kinds of optimizations needed for the project are also included. When the project size grows, build offers a standardized method for building the project.

7. How are CLASSPATH and PATH different from each other in terms of J2EE?

Key environmental variables utilized by Java systems include PATH and CLASSPATH.

  • Whether Java is installed on the system or not has no bearing on PATH, a system-level variable. While JVM uses CLASSPATH, which is entirely Java-specific, to load the classes needed by running Java programmes.
  • The JDK binaries or native libraries like java.exe are referenced by the PATH variable. In contrast, the CLASSPATH variable directs users to Java binaries, such as bytecode-filled JAR files.

8. How is a multi tier client server architectural model advantageous?

The tiers that make up a multi-tier client-server architectural model all communicate with one another. The three-tier application paradigm shown below shows how the client/presentation, business logic, and database tiers interact with one another to handle requests and provide responses:

  • The user interface and business logic can both be altered independently.
  • Each tier may be individually coded or designed. Java or Python, for instance, can be used to code the intermediate tier, while Angular or React can be used to code the client tier, etc.
  • Between the components, abstraction is introduced. As an illustration, the client tier can access data without being aware of the origin of the response, the server infrastructure in the backend, etc.
  • Instead of needing to create a new connection for each user, the database may feature pooled connections that allow users to share data.

9. Why do we have JNDI and JDBC in J2EE?

JDBC, or Java Database Connectivity, offers instructions and APIs for establishing connections to databases from many vendors, including MySQL, Oracle, PostgreSQL, etc., in order to obtain data. Without knowing the precise host address or port, JNDI (Java Naming and Directory Interface) assists in creating a logical framework to access a resource from the database, EJB beans, messaging queues, etc. After registering a resource with JNDI, application components can subsequently be accessed by using the JNDI name.

10. What are the J2EE aplets? Why can we use it?

Applets are Java-based J2EE client components that run in a web browser or on a number of other platforms that support the applet development model. They assist in providing small, portable embedded Java programmes in HTML pages that will be run automatically when we browse the pages and are used to provide interactive capabilities to online apps.

11. What is EJB? How can you use it in J2EE?

One of the most crucial components of the J2EE platform, EJB, or Enterprise Java Beans, enables the creation and deployment of enterprise-level multi-tiered applications while keeping performance, scalability, and robustness in mind. When we wish to accomplish the following, we can utilize EJBs:

  • Clustering: EJBs can be utilized for the application's deployment in a cluster environment to provide high availability and fault tolerance.
  • Concurrency without using Threads: Due to the fact that EJBs are available in the EJB container and are instantiated using the object pool, concurrency can be achieved without the usage of actual threads. This aids in achieving performance without engaging Threads-related complexity.

12. What is the architecture model of Struts?

Strut is an application development framework for creating enterprise-level applications that combines JSP, Java Servlets, messages, and custom tags. MVC (Model-View-Controller) architecture is the foundation of it.

  • View: JSP technology is used by Struts to develop views for enterprise-level applications.
  • Model: The internal system state is defined by this component. Depending on the architecture of the application, it could either be a Java Beans cluster or a single bean.
  • Controller:It manages user actions that process requests and give answers to them. It is a servlet.

13. What is ORM?

By leveraging metadata that describes the relationship between the database and the objects, object-relational mapping, or ORM, converts Java class objects to tables in relational databases and vice versa.

14. What constitutes web components?

Web components are made up of Java Servlets and Java Server Pages (JSP) elements. Java Servlets process requests and responses on the fly. Servlets that enable a natural method to create static content are executed through JSP pages.

15. What is EJB platform?

The Enterprise JavaBeans are referred to as EJBs. While you focus on building business logic, the EJB platform handles tasks like transaction and state management, resource pooling, multithreading, and simple searches.

16. What is JSF?

JSF, or Java Server Faces, is a web framework designed to make the creation of user interfaces more straightforward. It is a common display solution for web applications with a Java foundation. It offers reusable UI components and is built on the MVC (Model-View-Controller) pattern.

17. What factors should a J2EE application possess for operating in a global economy?

The following are the factors that a J2EE application possess for operating in a global economy:

  • Language Requirements: For a wider user base, a programme should support the national language as well as regional ones.
  • Financial Consideration: Depending on the government, every nation has its own taxes, regulations, and tariffs. When creating a J2EE application, all of these elements should be taken into account.
  • Legal Differences: Every government has its own set of customary laws, privacy laws, and demands for every nation. A designed application must abide by all applicable laws.

18. What are Connectors? Describe the Connector Architecture.

Connectors are used to offer connectivity to various enterprise information systems through standard extension protocols. Resource adapters and system-level contracts, both of which are unique to enterprise information systems, make up a connector architecture. Plugging the resource adapters into the container. For a resource adapter to be plugged into J2EE applications, it must satisfy certain contracts that the connector architecture prescribes, such as security, transaction, resource management, etc.

19. What are the design goals of J2EE architecture?

The following are the design goals of J2EE architecture:

  • User Interaction: The user experience should be smooth and connect to a variety of devices, including computers, mobile phones, laptops, etc.
  • Data Connectivity: A J2EE application's link to legacy systems needs to be stable enough to support business operations.
  • Service Availability: To guarantee that the application is accessible around-the-clock in order to meet necessary business objectives.
  • Ease of Accessibility: Applications should be accessible to users from any location and on any device.
  • Abstraction and Flexibility: The server should handle the configuration details while the developer should concentrate on the business logic.

20. What is JRMP?

JRMP, or Java Remote Method Protocol, is a tool used for Remote Method Invocation (RMI), which allows Java objects to be passed as arguments. When moving items from one JVM to another using object serialization, RMI uses this underlying protocol to marshal objects as a stream.

21. How is 32-bit JVM different from 64-bit JVM?

In contrast to 32-bit operating systems, 64-bit operating systems use the 64-bit JVM. As opposed to the 4G limit of 32-bit JVM, we can select higher heap size memory in 64-bit JVM up to 100G. When running in a 64-bit JVM, Java programmes consume more memory than when running in a 32-bit JVM. The Ordinary Object Pointer's larger size is to blame for this. However, this can be avoided by instructing the JVM to utilize 32-bit pointers by using the -XXCompressedOOP option. In contrast to the 32-bit JVM, which utilizes 8-byte headers and a maximum of 4-byte internal references, the 64-bit JVM employs 12-byte object headers and a maximum of 8-byte internal references.

22. What is the purpose of heap dumps and how do you analyze a heap dump?

Heap dumps are a snapshot of all active objects being used by active Java programmes on the Java heap memory. The heap dump contains comprehensive information for each item, including type, class name, address, size, and relationships to other objects. Numerous tools are useful when examining Java heap dumps. For instance, JDK itself offers the jhat tool for heap dump analysis. Heap dumps are also used for memory leak analysis. Memory leaks are a phenomenon that happens when there are objects that are no longer needed by the application but are still represented as referenced objects by the garbage collection, making it impossible to free that memory. Following are the causes that result in memory leaks:

  • Constantly creating new instances of objects without relinquishing them.
  • Open connection objects, such as database connections, post the necessary operation.
  • Static variables preserving object references.
  • Adding objects to a hashmap without modifying the equals() method of the hash code. If these techniques are left out, the hashmap will continue to expand while taking duplicates into account.
  • Infinite caches.
  • Techniques that are uninvoked by listeners.

As a result, the application keeps using more and more memory, which finally causes OutOfMemory Errors and can cause the application to crash. To find memory leaks in heap dumps, we can analyze the data using the visualVM for Eclipse Memory Analyzer tools.

23. What are EAR, WAR, and JAR?

Enterprise Archive File, or EAR, is a compressed and packaged file that contains client, EJB, and web components. Its extension is.ear. We can deploy many modules simultaneously to the application server using EAR files.

The term "WAR" refers to a file that contains all web components that have been compressed and packaged together. This file makes it simple to test and deploy web apps with just one request.

Java Archive file is referred to as a JAR. It includes all of the class files and libraries that make up APIs. The.jar file contains these compressed and packaged together. These are employed for the single-request deployment of the full application, including classes and resources.

24. What is Spring?

A lightweight open source framework for creating enterprise apps is called Spring. It solves the enterprise application development complexity and offers simple J2EE development. Rod Johnson was the author of the original draught. In June 2003, it was made available under the Apache 2.0 license.

25. What is Hibernate?

Hibernate is a Java-based Object Relational Mapper technology that offers an abstraction layer for accessing or changing database data. The developer should not worry about how the connections to the databases are formed, how the data translation from Java application to Database and vice versa occurs because it handles all implementations inside. Strong object-oriented concepts supported by Hibernate include inheritance, association, polymorphism, compositions, and collections that aid in query creation when using the Java method and HQL (Hibernate Query Language).

26. Can you describe the phases of the servlet life cycle?

Given below are the five phases:

  • Classloading phases: The web container must first load the servlet class file with the.class extension.
  • Instantiation phases: The servlet must then be instantiated by executing the default function Object.
    • Initialize phases: This stage involves running the servlet's init() method, where the servlet configuration will be given to it. This is a lifecycle method offered by the Servlet interface that is only executed once during the lifetime of the servlet.
  • Request handling: By utilizing the service() function of the Servlet interface, the servlets in this instance deliver services to various requests.
  • Remove phases: The Servlet interface destroy() lifecycle method, which is used to clear the configuration and close resources before servlet destruction, will be called during this phase. The waste will then be picked up after this.

27. What are different modules used in Spring?

Given below are the various modules used in Spring:

  • The Core container module
  • Object/Relational mapping module
  • DAO module
  • Application context module
  • Aspect Oriented Programming
  • Web module
  • MVC module

28. What is a backing bean?

Backing beans are JavaBeans components that relate to JavaServer Pages and contain JavaServer Faces components. The backing bean outlines the characteristics for the page components as well as the methods that process them. Event handling, validation, and navigational processing are a few examples of this processing.

29. What is the build file?

An XML file with one or more asant targets is referred to as a build file. A target is a list of assignments that a user hopes to complete. A user can specify which target should be executed when asant is started. If there isn't a target, the project's default target is carried out.

30. Explain business logic.

The code that contains an application's functionality is known as business logic. This logic is implemented in the EJB (Enterprise JavaBeans) architecture by the enterprise bean's methods.

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J2EE establishes standards and specifications for a number of different parts, including e-mailing, database connectivity, security, XML parsing, CORBA communication, etc., that aid in the creation of sophisticated, dependable, secure, and distributed servlets and client-server applications. It offers a number of API interfaces that serve as standards for vendor adapters from various companies and J2EE components. This makes sure that vendor programmes are not a dependency of the application components. As a result, Java developers working in the software development industry have a strong preference for J2EE. 

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