Java Programing

Manifest-Version: 1.0 Created-By: 1.2.1 (Sun Microsystems Inc.) Basically the file just describes its version number. In SDK 1.1, the manifest contains entries describing each item in the archive. In our case, the beginning of our manifest file looks like this (in SDK 1.1 only): Manifest-Version: 1.0 Name: spaceblaster/game/Game.class Digest-Algorithms: SHA MD5 SHA-Digest: D5Vi4UV+O+XprdFYaUt0bCv2GDo= MD5-Digest: 9/W62mC4th6G/x8tTnP2Ng== Name: spaceblaster/game/Planetoid.class Digest-Algorithms: SHA MD5 SHA-Digest: SuSUd6pYAASO5JiIGlBrWYzLGVk= MD5-Digest: KN/4cLDxAxDk/INKHi2emA== … The first line is the same version number as before. Following it are groups of lines describing each item. The first line tells you the item’s name; in this case, the lines describing the files Game.class and Planetoid.class. The remaining lines in each section describe various attributes of the item. In this case, the Digest-Algorithms line specifies that the manifest provides message digests (similar to checksums) in two forms: SHA and MD5.[2] This is followed by the actual message digest for the item, computed using these two algorithms. [2] SHA and MD5 stand for Secure Hashing Algorithm and Message Digest 5. That’s all you really need to know about them; an explanation of these algorithms is beyond the scope of this book. As we’ll discuss in the next section, the META-INF directory and manifest file can also hold digital signature information for items in the archive. Since the message digest information is really necessary only for signed JAR files, it is omitted when you create an archive in SDK 1.2 and later. You can add your own information to the manifest descriptions by specifying a supplementary manifest file when you create the archive. This is a good place to store other simple kinds of attribute information about the files in the archive, perhaps version or authorship information. For example, we can create a file with the following keyword: value lines: Name: spaceblaster/images/planetoid.gifRevisionNumber: 42.7 Artist-Temperment: moody To add this information to the manifest in our archive, place it in a file called myManifest.mf and give the following jar command: % jar -cvmf myManifest.mf spaceblaster.jar spaceblaster We’ve added an additional option to the command, m, which specifies that jar should read additional manifest information from the file given on the command line. How does jar know which file is which? Because m is before f, it expects to find the manifest information before the name of the JAR file it will create. If you think that’s awkward, you’re right; get the names in the wrong order, and jar will do the wrong thing. Be careful. - 64

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