Package io.pack200

Class Pack200


  • public abstract class Pack200
    extends java.lang.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 io.pack200.Pack200;
        import io.pack200.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
    Author:
    John Rose, Kumar Srinivasan
    • Nested Class Summary

      Nested Classes 
      Modifier and Type Class Description
      static interface  Pack200.Packer
      The packer engine applies various transformations to the input JAR file, making the pack stream highly compressible by a compressor such as gzip or zip.
      static interface  Pack200.Unpacker
      The unpacker engine converts the packed stream to a JAR file.
    • Method Summary

      All Methods Static Methods Concrete Methods 
      Modifier and Type Method Description
      static Pack200.Packer newPacker()
      Obtain new instance of a class that implements Packer.
      static Pack200.Unpacker newUnpacker()
      Obtain new instance of a class that implements Unpacker.
      • Methods inherited from class java.lang.Object

        clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait
    • Method Detail

      • newPacker

        public static Pack200.Packer newPacker()
        Obtain new instance of a class that implements Packer.
        • If the system property io.pack200.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 io.pack200.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.