J2EE FAQs or Interview Questions

J2EE FAQs or Interview Questions.

1.What is J2EE?
J2EE is an environment for developing and deploying enterprise applications. The J2EE platform consists of a set of services, application programming interfaces (APIs), and protocols that provide the functionality for developing multi tiered, and web-based applications.

2. What is the J2EE module?
A J2EE module consists of one or more J2EE components for the same container type and one component deployment descriptor of that type.

3.What are the components of J2EE application?
A J2EE component is a self-contained functional software unit that is assembled into a J2EE application with its related classes and files and communicates with other components. The J2EE specification defines the following J2EE components:
o Application clients and applets are client components.
o Java Servlets and Java Server Pages TM (JSPTM) technology components are web components.
o Enterprise JavaBeansTM (EJBTM) components (enterprise beans) are business components.
o Resource adapter components provided by EIS and tool vendors.

4. What are the four types of J2EE modules?
1. Application client module
2. Web module
3. Enterprise JavaBeans module
4. Resource adapter module
5. What does application client module contain?

The application client module contains:
o class files,
o an application client deployment descriptor.
Application client modules are packaged as JAR files with a .jar extension.

6. What does Enterprise JavaBeans module contain?
The Enterprise JavaBeans module contains:
o class files for enterprise beans
o An EJB deployment descriptor.
EJB modules are packaged as JAR files with a .jar extension.

7.What does resource adapt module contain?
The resource adapt module contains:
o all Java interfaces,
o classes,
o native libraries,
o other documentation,
o A resource adapter deployment descriptor.
Resource adapter modules are packages as JAR files with a .rar (Resource adapter Archive) extension.

8.How many development roles are involved in J2EE application?
There are at least 5 roles involved:

1. Enterprise Bean Developer
* Writes and compiles the source code
* Specifies the deployment descriptor
* Bundles the .class files and deployment descriptor into an EJB JAR file
2. Web Component Developer
* Writes and compiles Servlets source code
* Writes JSP and HTML files
* Specifies the deployment descriptor for the Web component
* Bundles the .class, .jsp, .html, and deployment descriptor files in the WAR file
3. J2EE Application Client Developer
* Writes and compiles the source code
* Specifies the deployment descriptor for the client
* Bundles the .class files and deployment descriptor into the JAR file
4. Application Assembler : The application assembler is the company or person who receives application component JAR files from component providers and assembles them into a J2EE application EAR file. The assembler or deployer can edit the deployment descriptor directly or use tools that correctly add XML tags according to interactive selections. A software developer performs the following tasks to deliver an EAR file containing the J2EE application:
* Assembles EJB JAR and WAR files created in the previous phases into a J2EE application (EAR) file
* Specifies the deployment descriptor for the J2EE application
* Verifies that the contents of the EAR file are well formed and comply with the J2EE specification
5. Application Deployer and Administrator
* Configures and deploys the J2EE application
* Resolves external dependencies
* Specifies security settings & attributes
* Assigns transaction attributes and sets transaction controls
* Specifies connections to databases
* Deploys or installs the J2EE application EAR file into the J2EE server
* Administers the computing and networking infrastructure where J2EE applications run
* Oversees the runtime environment
But a developer role depends on the job assignment. For a small company, one developer may take these 5 roles altogether.

9. What is difference between J2EE 1.3 and J2EE 1.4?
J2EE 1.4 is an enhancement version of J2EE 1.3. It is the most complete Web services platform ever.
J2EE 1.4 includes:
o Java API for XML-Based RPC (JAX-RPC 1.1)
o SOAP with Attachments API for Java (SAAJ),
o Web Services for J2EE(JSR 921)
o J2EE Management Model(1.0)
o J2EE Deployment API(1.1)
o Java Management Extensions (JMX),
o Java Authorization Contract for Containers(JavaACC)
o Java API for XML Registries (JAXR)
o Servlet 2.4
o JSP 2.0
o EJB 2.1
o JMS 1.1
o 2EE Connector 1.5

The J2EE 1.4 features complete Web services support through the new JAX-RPC 1.1 API, which supports service endpoints based on Servlets and enterprise beans. JAX-RPC 1.1 provides interoperability with Web services based on the WSDL and SOAP protocols.

The J2EE 1.4 platform also supports the Web Services for J2EE specification (JSR 921), which defines deployment requirements for Web services and utilizes the JAX-RPC programming model.

In addition to numerous Web services APIs, J2EE 1.4 platform also features support for the WS-I Basic Profile 1.0. This means that in addition to platform independence and complete Web services support, J2EE 1.4 offers platform Web services interoperability.

The J2EE 1.4 platform also introduces the J2EE Management 1.0 API, which defines the information model for J2EE management, including the standard Management EJB (MEJB). The J2EE Management 1.0 API uses the Java Management Extensions API (JMX).

The J2EE 1.4 platform also introduces the J2EE Deployment 1.1 API, which provides a standard API for deployment of J2EE applications.

The J2EE 1.4 platform includes security enhancements via the introduction of the Java Authorization Contract for Containers (JavaACC). The JavaACC API improves security by standardizing how authentication mechanisms are integrated into J2EE containers.

The J2EE platform now makes it easier to develop web front ends with enhancements to Java Servlet and JavaServer Pages (JSP) technologies. Servlets now support request listeners and enhanced filters. JSP technology has simplified the page and extension development models with the introduction of a simple expression language, tag files, and a simpler tag extension API, among other features. This makes it easier than ever for developers to build JSP-enabled pages, especially those who are familiar with scripting languages.

Other enhancements to the J2EE platform include the J2EE Connector Architecture, which provides incoming resource adapter and Java Message Service (JMS) plug ability. New features in Enterprise JavaBeans (EJB) technology include Web service endpoints, a timer service, and enhancements to EJB QL and message-driven beans.

The J2EE 1.4 platform also includes enhancements to deployment descriptors. They are now defined using XML Schema which can also be used by developers to validate their XML structures.

Note: The above information comes from SUN released notes.

10. Is J2EE application only a web-based?
NO. A J2EE application can be web-based or non-web-based. If an application client executes on the client machine, it is a non-web-based J2EE application. The J2EE application can provide a way for users to handle tasks such as J2EE system or application administration. It typically has a graphical user interface created from Swing or AWT APIs, or a command-line interface. When user request, it can open an HTTP connection to establish communication with a Servlet running in the web tier.