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And What About This JARDiff Stuff?

JARDiff is a mechanism for updating incrementally JAR files. It is a part of the JNLP specification, but it can be used outside usual JNLP deployment as well. Figure 4 shows its mechanism.

Figure 4 The JARDiff working mechanism.

As discussed, the JARDiff format is a way to perform incremental updates to a JAR file. It consists of a special JAR file sent to the client, which describes the differences between two JAR files—OldJAR and NewJAR, for example.

The differencing information is stored in the META-INF/INDEX.JD text file, which describes the copies of new or changed files in the NewJAR file relative to the OldJAR file.

The file is composed of lines <command> space <value>. The first line describes the JARDiff format version (currently 1.0):

version <version>

And following are lines of two types:

remove <fully qualified class in OldJar but not in NewJAR>
move <fully qualified class in OldJAR> <fully qualified class in NewJAR >.

They describe the differences between the already installed OldJAR file and the to-be-installed NewJAR file.

The following sections summarize the pros and cons of using JNLP.

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