JavaTM Archive (JAR) Features

Documentation Contents
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.

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.

JAR File Specification and Overview JAR Files and the Extensions Framework Enhanced Jar Tool Reading and Writing JAR Files: API Specification

The API of classes and java.util.jar have been enhanced with the addition of the following: The previous implementation of caching downloaded Jar files created problems for long-running server application and for RMI. Each open JarURLConnection creates a temporary local file that holds Jar-file date, and a JarFile object is created on top of the temporary file. Because the open file handle/descriptor on each temporary file was never closed, the files could quickly take up disk space for long-running server applications. The new API provides a solution for this problem by supporting a new "delete-on-close" mode for opening Zip and Jar files.

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