Tutorial: Lesson: Packaging Programs in JAR Files

The Java^TM Archive (JAR) file format enables you to bundle multiple files into a single archive file. Typically a JAR file contains the class files and auxiliary resources associated with applets and applications.

The JAR file format provides many benefits:

• Security: You can digitally sign the contents of a JAR file. Users who recognize your signature can then optionally grant your software security privileges it wouldn't otherwise have.

• Decreased download time: If your applet is bundled in a JAR file, the applet's class files and associated resources can be downloaded to a browser in a single HTTP transaction without the need for opening a new connection for each file.

• Compression: The JAR format allows you to compress your files for efficient storage.

• Packaging for extensions: The extensions framework provides a means by which you can add functionality to the Java core platform, and the JAR file format defines the packaging for extensions. Java 3D™ and JavaMail™ are examples of extensions developed by Sun^TM. By using the JAR file format, you can turn your software into extensions as well.

• Package Sealing: Packages stored in JAR files can be optionally sealed so that the package can enforce version consistency. Sealing a package within a JAR file means that all classes defined in that package must be found in the same JAR file.

• Package Versioning: A JAR file can hold data about the files it contains, such as vendor and version information.

• Portability: The mechanism for handling JAR files is a standard part of the Java platform's core API...

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Courtesy:- http://java.sun.com/