The Apache Commons Compress library defines an API for working with ar, cpio, Unix dump, tar, zip, gzip, XZ, Pack200, bzip2, 7z, arj, lzma, snappy, DEFLATE and Z files.
The code in this component has many origins:
The current release is 1.8.1 and requires Java 5.
Below we highlight some new features, for a full list of changes see the Changes Report.
Compress 1.8.1 is a bug fix release with fixes for the tar, ar and snappy formats as well as the IOUtils class. In addition CompressorStreamFactory can now autodetect the .Z compress format.
The compress component is split into compressors and archivers. While compressors (un)compress streams that usually store a single entry, archivers deal with archives that contain structured content represented by ArchiveEntry instances which in turn usually correspond to single files or directories.
Currently the bzip2, Pack200, XZ, gzip, lzma and Z formats are supported as compressors where gzip support is mostly provided by the java.util.zip package and Pack200 support by the java.util.jar package of the Java class library. XZ and lzma support is provided by the public domain XZ for Java library. As of Commons Compress 1.8.1 support for the lzma, Z and Snappy formats is read-only.
The ar, arj, cpio, dump, tar, 7z and zip formats are supported as archivers where the zip implementation provides capabilities that go beyond the features found in java.util.zip. As of Commons Compress 1.8.1 support for the dump and arj formats is read-only - 7z can read most compressed and encrypted archives but only write unencrypted ones. LZMA(2) support in 7z requires XZ for Java as well.
The compress component provides abstract base classes for compressors and archivers together with factories that can be used to choose implementations by algorithm name. In the case of input streams the factories can also be used to guess the format and provide the matching implementation.