Pack200

abstract class Pack200

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:

<code>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 (&gt;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();
     }
  </code>

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

Public methods

open static fun newPacker(): Pack200.Packer!

open static fun newUnpacker(): Pack200.Unpacker!