Added in API level 1

Pack200

abstract class Pack200
kotlin.Any
   ↳ java.util.jar.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

Nested classes
abstract

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.
abstract

The unpacker engine converts the packed stream to a JAR file.
Public methods
open static Pack200.Packer!

Obtain new instance of a class that implements Packer.
open static Pack200.Unpacker!

Obtain new instance of a class that implements Unpacker.

Public methods

newPacker

Added in API level 1
open static fun newPacker(): Pack200.Packer!

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.

Return
Pack200.Packer! A newly allocated Packer engine.

newUnpacker

Added in API level 1
open static fun newUnpacker(): Pack200.Unpacker!

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.

Return
Pack200.Unpacker! A newly allocated Unpacker engine.