# Package org.apache.commons.compress.compressors.pack200

package org.apache.commons.compress.compressors.pack200

Provides stream classes for compressing and decompressing streams using the Pack200 algorithm used to compress Java archives.

The streams of this package only work on JAR archives, i.e. a `Pack200CompressorOutputStream` expects to be wrapped around a stream that a valid JAR archive will be written to and a `Pack200CompressorInputStream` provides a stream to read from a JAR archive.

JAR archives compressed with Pack200 will in general be different from the original archive when decompressed again. For details see the API documentation of Pack200.

The streams of this package work on non-deflated streams, i.e. archives like those created with the `--no-gzip` option of the JDK's `pack200` command line tool. If you want to work on deflated streams you must use an additional stream layer - for example by using Apache Commons Compress' gzip package.

The Pack200 API provided by the Java class library doesn't lend itself to real stream processing. `Pack200CompressorInputStream` will uncompress its input immediately and then provide an `InputStream` to a cached result. Likewise `Pack200CompressorOutputStream` will not write anything to the given OutputStream until `finish` or `close` is called - at which point the cached output written so far gets compressed.

Two different caching modes are available - "in memory", which is the default, and "temporary file". By default data is cached in memory but you should switch to the temporary file option if your archives are really big.

Given there always is an intermediate result the `getBytesRead` and `getCount` methods of `Pack200CompressorInputStream` are meaningless (read from the real stream or from the intermediate result?) and always return 0.

During development of the initial version several attempts have been made to use a real streaming API based for example on `Piped(In|Out)putStream` or explicit stream pumping like Commons Exec's `InputStreamPumper` but they have all failed because they rely on the output end to be consumed completely or else the `(un)pack` will block forever. Especially for `Pack200InputStream` it is very likely that it will be wrapped in a `ZipArchiveInputStream` which will never read the archive completely as it is not interested in the ZIP central directory data at the end of the JAR archive.

- Related Packages
  Package
  Description
  org.apache.commons.compress.compressors
  Provides a unified API and factories for dealing with compressed streams.
- Class
  Description
  Pack200CompressorInputStream
  An input stream that decompresses from the Pack200 format to be read as any other stream.
  Pack200CompressorOutputStream
  An output stream that compresses using the Pack200 format.
  Pack200Strategy
  The different modes the Pack200 streams can use to wrap input and output.
  Pack200Utils
  Utility methods for Pack200.