JAR File Format

The Java^TM Tutorial

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Trail: To 1.1 -- And Beyond!
Lesson: What's New in 1.1?

JAR File Format

JAR (Java ARchive) is a platform-independent file format that allows you to bundle a Java applet and its requisite components (.class files, images and sounds) into a single file. Using the new ARCHIVE attribute of the <APPLET> tag, this JAR file can be downloaded to a browser in a single HTTP transaction, greatly improving the download speed. In addition, JAR supports compression, which reduces the file size, further improving the download time.
Finally, the applet author can digitally sign individual entries in a JAR file to authenticate their origin. You read about this in Security and Signed Applets.
To help you get started, here's a brief introduction to some of the basics of using JAR files. You create and manipulate JAR files with the jar utility program. The command-line arguments to jar are similar to those of the UNIX tar program. Table 19 lists the most common manipulations of a JAR file along with the jar command or HTML tags for doing them.
To create a JAR file: jar cvf JARfilename listoffiles

To list the contents
of a JAR file: jar tvf JARfilename

To extract the entire
contents of a JAR file: jar xvf JARfilename

To extract a specific
file from a JAR file: jar xvf JARfilename FileToExtract
To specify the use of a
JAR file with an applet:
<applet code=AppletClassName.class
        archive="JarFileName.jar"
        width=width height=height>
</applet>

Where to Find Documentation

Please refer to the trail The Java Archive (JAR) File Format

. JAR files are also discussed in Combining an Applet's Files into a Single File

, which shows you how to use JAR files with your applets and talks about the benefits of doing so.

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To create a JAR file:	`jar cvf JARfilename listoffiles`
To list the contents of a JAR file:	`jar tvf JARfilename`
To extract the entire contents of a JAR file:	`jar xvf JARfilename`
To extract a specific file from a JAR file:	`jar xvf JARfilename FileToExtract`
To specify the use of a JAR file with an applet:	<applet code=AppletClassName.class archive="JarFileName.jar" width=width height=height> </applet>