| Zip files and Jar Files | Java Archive (JAR) files provide a compact way to store a number of classes or other data resources. | |
| The format of a jar file is similar to a zip file. | ||
| java.util.zip
java.util.jar |
Classes in java.util.zip and java.util.jar packages provide methods for reading writing data with steam methods that compress and decompress files. | |
| The JAR file format add a manifest file to the zip format. This file gives extra information about each of the data items in the file. | ||
| Extra information may include digital signatures to positively identify applications as coming from a know source. | ||
| Connection over a network is time consuming. Loading large classes across the network is slow. | ||
| JAR | A JAR file can be used to package an application classes and resources in a compressed file to be sent across the network. | |
| The JAR file can contain class files, images, sounds, applet, etc.. | ||
| JAR files can be used for application distribution. Specially Java beans. | ||
| Creating JAR files | The jar command can be used to create jar files. The options most likely used are: | |
| c | Create a new archive | |
| x | extract file from the archive | |
| f | specify the archive’s file name | |
| O | Don’t use zip to compress the file. This allows the placing of the JAR files in a directory in the current path. | |
| v | view the archive table contents. | |
| Creating a jar file: | ||
| jar –cf Jungle.jar Panther.class Leopard.class | ||
| Using a JAR in an Applet | <applet code=ExampleApplet.class
archive=”jars/example.jar” width=255 height=110 </applet> |
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| archive tag | The archive keyword is used to specify the JAR file to be used when the applect needs a class and other resources. | |
| The applet looks in the JAR file first, then on the server. | ||
| More than one JAR file can be define in the archive parameter. | ||