J2EE Interview Questions - FAQ Part 2

1. What is the purpose of the web container?
   
   Answer:
   Servlet and JSP containers are collectively referred to as Web containers.
   The web container manages the execution of JSP page and servlet components for J2EE applications.
   Web components and their containers run on the J2EE application server.

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2. What is the (EJB) Enterprise JavaBeans container?
   
   Answer:
   It manages the execution of enterprise beans for J2EE applications.
   Enterprise beans and their container run on the J2EE server.

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3. What is Applet container?
   
   Answer:
   The applet container manages the execution of applets.
   The applet container consists of a Web browser and Java Plugin running on the client together.

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4. How do we package J2EE components?
   
   Answer:
   J2EE components are packaged separately and bundled into a J2EE application for deployment.
   The following elements are assembled into a module and added to the J2EE application.
   1. Each component,
   2. its related files such as GIF and HTML files or server-side utility classes, and
   3. a deployment descriptor .
   
   A J2EE application is composed of one or more enterprise bean,Web, or application client component modules.
   The final enterprise solution can use one J2EE application or be made up of two or more J2EE applications.
   A J2EE application and each of its modules has its own deployment descriptor.
   A deployment descriptor is an XML document with an .xml extension that describes a component’s deployment settings.

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5. What is a thin client?
   
   Answer:
   A thin client is a lightweight interface to the application that does not have such operations like
   1. query databases,
   2. execute complex business rules, or
   3. connect to legacy applications.

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6. What are types of J2EE clients?
   
   Answer:
   The following are the types of J2EE clients:
   1. Applets
   2. Application clients
   3. Java Web Start-enabled rich clients, powered by Java Web Start technology.
   4. Wireless clients, based on Mobile Information Device Profile (MIDP) technology.

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7. What is a deployment descriptor?
   
   Answer:
   A deployment descriptor is an Extensible Markup Language (XML) text-based file with an .xml extension that describes a component’s deployment settings. A J2EE application and each of its modules has its own deployment descriptor. For example, an enterprise bean module deployment descriptor declares transaction attributes and security authorizations
   for an enterprise bean. Because deployment descriptor information is declarative, it can be changed without modifying the bean source code. At run time, the J2EE server reads the deployment descriptor and acts upon the component accordingly.

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8. What is the EAR file?
   
   Answer:
   An EAR file is a standard JAR file with an .ear extension, named from Enterprise Archive file.
   A J2EE application with all of its modules is delivered in an EAR file.

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9. What is JTA and JTS?
   
   Answer:
   1. JTA is the abbreviation for the Java Transaction API.
   2. JTS is the abbreviation for the Jave Transaction Service.
   
   JTA provides a standard interface and allows you to demarcate transactions in a manner that is independent of the transaction manager implementation. The J2EE SDK implements the transaction manager with JTS. But your code does not call the JTS methods directly. Instead, it invokes the JTA methods, which then call the lower-level JTS routines.
   Therefore, JTA is a high level transaction interface that your application uses to control transactions and JTS is a low level transaction interface.
   EJB uses behind the scenes (client code does not directly interact with JTS. It is based on object transaction service(OTS) which is part of CORBA. )

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10. What is JAXP?
    
    Answer:
    JAXP stands for Java API for XML.
    XML is a language for representing and describing text-based data which can be read and handled by any program or tool that uses XML APIs. It provides standard services
    1. to determine the type of an arbitrary piece of data,
    2. encapsulate access to it,
    3. discover the operations available on it,
    4. and create the appropriate JavaBeans component to perform those operations.