JAR Files
Java 1.1 added support for Java ARchive
files, JAR files for short. JAR files bundle the many different
classes, images, and sound files an applet requires into a single
file. It is generally faster for a web browser to download one JAR
file than to download the individual files the archive contains,
since only one HTTP connection is required. An applet stored in a JAR
file, instead of as merely loose .class files,
is embedded in a web page with an <applet>
tag with an archive
attribute pointing to the JAR
file. For example:
<applet code=NavigationMenu archive="NavigationMenu.jar" width=400 height=80> </applet>
The code
attribute still says that the main class
of this applet is called NavigationMenu
. However,
a Java 1.1 web browser, rather than asking the web server for the
file NavigationMenu.class
as a Java 1.0 web
browser would, asks the web server for the file
NavigationMenu.jar
. Then the browser looks
inside NavigationMenu.jar
to find the file
NavigationMenu.class
. Only if it doesn’t
find NavigationMenu.class
inside
NavigationMenu.jar
does it then go back to the
web server and ask for NavigationMenu.class
. Now
suppose the NavigationMenu
applet tries to load an
image called menu.gif
. The applet will look for
this file inside the JAR archive too. It only has to make a new
connection to the web server if it can’t find
menu.gif
in the archive.
Sun wisely decided not to attempt to define a new file format for JAR files. Instead, they stuck with the tried-and-true zip format. ...
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