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.

Summary

Inherited methods

From class java.lang.Object Object clone() Creates and returns a copy of this object. boolean equals(Object obj) Indicates whether some other object is "equal to" this one. void finalize() Called by the garbage collector on an object when garbage collection determines that there are no more references to the object. final Class<?> getClass() Returns the runtime class of this Object. int hashCode() Returns a hash code value for the object. final void notify() Wakes up a single thread that is waiting on this object's monitor. final void notifyAll() Wakes up all threads that are waiting on this object's monitor. String toString() Returns a string representation of the object. final void wait(long millis, int nanos) Causes the current thread to wait until another thread invokes the notify() method or the notifyAll() method for this object, or some other thread interrupts the current thread, or a certain amount of real time has elapsed. final void wait(long millis) Causes the current thread to wait until either another thread invokes the notify() method or the notifyAll() method for this object, or a specified amount of time has elapsed. final void wait() Causes the current thread to wait until another thread invokes the notify() method or the notifyAll() method for this object.

Public methods

Pack200.Packer newPacker ()

Pack200.Unpacker newUnpacker ()