IT. Expert System.

Java Standard Edition (SE)

Pack200


compact1, compact2, compact3
java.util.jar

Class Pack200



  • public abstract class Pack200
    extends Object
    Transforms a JAR file to or from a packed stream in Pack200 format. Please refer to Network Transfer Format JSR 200 Specification at http://jcp.org/aboutJava/communityprocess/review/jsr200/index.html

    Typically the packer engine is used by application developers to deploy or host JAR files on a website. The unpacker engine is used by deployment applications to transform the byte-stream back to JAR format.

    Here is an example using packer and unpacker:

    
        import java.util.jar.Pack200;
        import java.util.jar.Pack200.*;
        ...
        // Create the Packer object
        Packer packer = Pack200.newPacker();
    
        // Initialize the state by setting the desired properties
        Map p = packer.properties();
        // take more time choosing codings for better compression
        p.put(Packer.EFFORT, "7");  // default is "5"
        // use largest-possible archive segments (>10% better compression).
        p.put(Packer.SEGMENT_LIMIT, "-1");
        // reorder files for better compression.
        p.put(Packer.KEEP_FILE_ORDER, Packer.FALSE);
        // smear modification times to a single value.
        p.put(Packer.MODIFICATION_TIME, Packer.LATEST);
        // ignore all JAR deflation requests,
        // transmitting a single request to use "store" mode.
        p.put(Packer.DEFLATE_HINT, Packer.FALSE);
        // discard debug attributes
        p.put(Packer.CODE_ATTRIBUTE_PFX+"LineNumberTable", Packer.STRIP);
        // throw an error if an attribute is unrecognized
        p.put(Packer.UNKNOWN_ATTRIBUTE, Packer.ERROR);
        // pass one class file uncompressed:
        p.put(Packer.PASS_FILE_PFX+0, "mutants/Rogue.class");
        try {
            JarFile jarFile = new JarFile("/tmp/testref.jar");
            FileOutputStream fos = new FileOutputStream("/tmp/test.pack");
            // Call the packer
            packer.pack(jarFile, fos);
            jarFile.close();
            fos.close();
    
            File f = new File("/tmp/test.pack");
            FileOutputStream fostream = new FileOutputStream("/tmp/test.jar");
            JarOutputStream jostream = new JarOutputStream(fostream);
            Unpacker unpacker = Pack200.newUnpacker();
            // Call the unpacker
            unpacker.unpack(f, jostream);
            // Must explicitly close the output.
            jostream.close();
        } catch (IOException ioe) {
            ioe.printStackTrace();
        }
     

    A Pack200 file compressed with gzip can be hosted on HTTP/1.1 web servers. The deployment applications can use "Accept-Encoding=pack200-gzip". This indicates to the server that the client application desires a version of the file encoded with Pack200 and further compressed with gzip. Please refer to Java Deployment Guide for more details and techniques.

    Unless otherwise noted, passing a null argument to a constructor or method in this class will cause a NullPointerException to be thrown.

    Since:
    1.5
    • Method Detail

      • newPacker

        public static Pack200.Packer newPacker()
        Obtain new instance of a class that implements Packer.
        • If the system property java.util.jar.Pack200.Packer is defined, then the value is taken to be the fully-qualified name of a concrete implementation class, which must implement Packer. This class is loaded and instantiated. If this process fails then an unspecified error is thrown.

        • If an implementation has not been specified with the system property, then the system-default implementation class is instantiated, and the result is returned.

        Note: The returned object is not guaranteed to operate correctly if multiple threads use it at the same time. A multi-threaded application should either allocate multiple packer engines, or else serialize use of one engine with a lock.

        Returns:
        A newly allocated Packer engine.
      • newUnpacker

        public static Pack200.Unpacker newUnpacker()
        Obtain new instance of a class that implements Unpacker.
        • If the system property java.util.jar.Pack200.Unpacker is defined, then the value is taken to be the fully-qualified name of a concrete implementation class, which must implement Unpacker. The class is loaded and instantiated. If this process fails then an unspecified error is thrown.

        • If an implementation has not been specified with the system property, then the system-default implementation class is instantiated, and the result is returned.

        Note: The returned object is not guaranteed to operate correctly if multiple threads use it at the same time. A multi-threaded application should either allocate multiple unpacker engines, or else serialize use of one engine with a lock.

        Returns:
        A newly allocated Unpacker engine.


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