Module java.base
Package 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

    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 the Java Deployment Guide for techniques and details.

    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.