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There are no STRUCTURAL differences between the files; they are all archived using zip-jar compression.
However, they are intended for different purposes.
--Jar files (files with a .jar extension) are intended to hold generic libraries of Java CLASSES, resources, auxiliary files, ETC.
--War files (files with a .war extension) arre intended to contain complete Web applications. In this context, a Web APPLICATION is defined as a single group of files, classes, resources, .jar files that can be packaged and accessed as one servlet context.
--Ear files (files with a .ear extension) arre intended to contain complete enterprise applications. In this context, an enterprise application is defined as a collection of .jar files, resources, classes, and multiple Web applications.
Each type of file (.jar, .war, .ear) is PROCESSED uniquely by application servers, servlet containers, EJB containers, etc.

There are no structural differences between the files; they are all archived using zip-jar compression.
However, they are intended for different purposes.
--Jar files (files with a .jar extension) are intended to hold generic libraries of Java classes, resources, auxiliary files, etc.
--War files (files with a .war extension) arre intended to contain complete Web applications. In this context, a Web application is defined as a single group of files, classes, resources, .jar files that can be packaged and accessed as one servlet context.
--Ear files (files with a .ear extension) arre intended to contain complete enterprise applications. In this context, an enterprise application is defined as a collection of .jar files, resources, classes, and multiple Web applications.
Each type of file (.jar, .war, .ear) is processed uniquely by application servers, servlet containers, EJB containers, etc.

The web MODULE contains:
--JSP FILES,
--class files for SERVLETS,
--GIF and HTML files, and
--a Web deployment descriptor.
Web modules are packaged as JAR files with a .war (Web ARchive) extension.

The web module contains:
--JSP files,
--class files for servlets,
--GIF and HTML files, and
--a Web deployment descriptor.
Web modules are packaged as JAR files with a .war (Web ARchive) extension.

The application client MODULE CONTAINS:
--CLASS files,
--an application client DEPLOYMENT descriptoor.
Application client modules are packaged as JAR files with a .jar extension.

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

1. Application client MODULE
2. WEB module
3. Enterprise JavaBeans module
4. Resource ADAPTER module.

1. Application client module
2. Web module
3. Enterprise JavaBeans module
4. Resource adapter module.

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:

Application CLIENTS and applets are client components.

Java Servlet and JavaServer PagesTM (JSPTM) technology components are web components.

Enterprise JavaBeansTM (EJBTM) components (enterprise beans) are BUSINESS components.

Resource adapter components provided by EIS and tool vendors.

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:

Application clients and applets are client components.

Java Servlet and JavaServer PagesTM (JSPTM) technology components are web components.

Enterprise JavaBeansTM (EJBTM) components (enterprise beans) are business components.

Resource adapter components provided by EIS and tool vendors.

A J2EE module consists of one or more J2EE COMPONENTS for the same CONTAINER TYPE and one component DEPLOYMENT descriptor of that type.

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

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 multitiered, web-based applications.

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 multitiered, web-based applications.