JavaTM Archive (JAR) Features
JAR (Java Archive) is a platform-independent file format that aggregates many files into one. Multiple Java applets and their requisite components (.class files, images and sounds) can be bundled in a JAR file and subsequently downloaded to a browser in a single HTTP transaction, greatly improving the download speed. The JAR format also supports compression, which reduces the file size, further improving the download time. In addition, the applet author can digitally sign individual entries in a JAR file to authenticate their origin. It is fully backward-compatible with existing applet code and is fully extensible.JAR File Specification and Overview
This version of the Java platform extends the utility of the JAR format. Enhancements include added functionality for the command-line JAR tool for creating Jar-file indexes for faster access to Jar-file contents. There are also new standard APIs for a "delete-on-close" mode for opening Jar files.
The API of classes java.util.zip and java.util.jar have been enhanced with the addition of the following:Tutorial
On the Java Software website: