Developing Java Beans

Using JAR Files with HTML

Since JAR files allow us to package a collection of files into one, and to compress the archive, they offer the opportunity to improve the download performance of applets that are retrieved from the Web via HTTP transactions. Basically, we can download the entire archive file in a single HTTP transaction. This reduces the number of trips we must make over the network to get all of the classes and associated files needed for an applet. Without an archive, multiple HTTP transactions may be required to download the required class files. There is also a performance boost because the archive can be compressed, reducing the download time.

The ARCHIVES Attribute

The ARCHIVES attribute is used in the HTML file to indicate that an archive file is used. The filename is relative to the location of the HTML page. Let’s look at the HTML file we used for running the PickleUser applet from the previous chapter:

<APPLET 
  ARCHIVE="BeansBook.jar"
  CODE=PickleUser.class 
  WIDTH=350 
  HEIGHT=125>
</APPLET>

The ARCHIVES attribute specifies that the BeansBook.jar archive file should be downloaded. Class files will be searched for in the specified archive first. If the class is not found in the archive, then the normal mechanism of searching the server and local file system will be used. Notice that the CODE attribute is still used to specify the starting class for the applet.

When you run this HTML file with appletviewer, the PickleUser class will be loaded from the archive. The applet ...