J2EE Components and Deployment

J2EE (Java 2 Enterprise Edition) components are written in Java. The 'Java' in the name indicates the programming language. C, C++, and C# are not used for J2EE components.

The statement is False. HTML pages and applets are client-side technologies that execute in the browser on the client machine, not on the J2EE server. The J2EE server serves these resources but doesn't manage or execute them - that happens on the client side.

Java Bean is NOT a J2EE container or application component. The J2EE containers are: Application Client Container, Applet Container, Web Container (for servlets/JSP), and EJB Container (for enterprise beans). JavaBean is a Java class convention for reusable components, not a J2EE container type.

The statement is False. J2EE components cannot interact directly - they must go through protocols and APIs defined by the J2EE specification. For example, web components communicate with EJBs through remote/local interfaces, not direct method calls. This loose coupling enables the container's services (transactions, security, etc.).

Page bean is NOT a valid enterprise bean type. EJB specification defines only three types: session beans (stateful/stateless), entity beans (now replaced by JPA entities), and message-driven beans. There is no such thing as a 'page bean' in EJB.

The deployment descriptor is an XML file that contains configuration information for J2EE components. It describes how the application should be deployed, including settings for servlets, EJBs, security roles, and resource references. The descriptor allows the application assembler and deployer to customize the application without modifying source code.

A Resource Adapter is a system-level software driver that connects a Java application to an Enterprise Information System (EIS). It implements the JCA (Java Connector Architecture) specification and provides connectivity to external resources like databases, legacy systems, or ERP systems. The other options are not standard J2EE terminology.

Applets run within a browser sandbox and are subject to strict security restrictions. They cannot directly access databases or other resources on the client or server for security reasons. Application clients, web components, and EJBs can all access databases when properly configured, making applet the only component that generally cannot.

JDBC (Java Database Connectivity) is the standard Java API for connecting to relational databases. It provides methods to execute SQL queries, retrieve results, and manage database transactions. JMS is for messaging, Java IDL for CORBA connectivity, and JAF (JavaBeans Activation Framework) for handling MIME data types.

Java IDL (Interface Definition Language) allows Java applications to invoke external CORBA objects using the IIOP (Internet Inter-ORB Protocol). It provides interoperability between Java and CORBA-based systems. JDBC is for databases, JMS for messaging, and JAF for data type handling.

EAR (Enterprise Archive) files contain all modules of a J2EE application - web modules (WAR), EJB modules (JAR), and resource adapters (RAR). It is the complete deployment unit. WAR files are for web components only, JAR for EJBs or Java classes, and RAR for resource adapters.

EJB components are packaged as JAR (Java Archive) files, which contain the enterprise bean classes and deployment descriptors. The deployment descriptor (ejb-jar.xml) provides configuration information. WAR is for web components, EAR for complete applications, and RAR for resource adapters.

Web components (servlets, JSPs, HTML pages) are packaged as WAR (Web Application Archive) files. The WAR contains the web components, deployment descriptor (web.xml), and static content. JAR is for EJBs, EAR for complete applications, and RAR for resource adapters.

Application client modules are packaged as JAR files containing the client classes and deployment descriptor. The client can be a standalone Java application or a web-based client. WAR is for web components, EAR for complete applications, and RAR for resource adapters.

The correct installation sequence is: first add the EAR file to the server, then configure the deployment descriptor settings, verify the content meets J2EE specifications, and finally deploy. You must add the application before configuring its deployment settings, and verification should occur before actual deployment.

J2EE products from different vendors can support different databases. For example, one application server might support Oracle, DB2, and SQL Server, while another might support MySQL and PostgreSQL. The J2EE specification does not mandate specific database support, leaving it to vendor implementation.

Entity beans are designed for persistent data storage and automatically handle database operations. The container manages the underlying SQL and JDBC calls, allowing developers to work with Java objects instead of writing database code. Session beans handle business logic, message-driven beans process JMS messages.