XZ for Java

Introduction

XZ for Java aims to be a complete implementation of XZ data compression in pure Java.

Features:

• Full support for the .xz file format specification version 1.2.1
• Single-threaded streamed compression and decompression
• Single-threaded decompression with limited random access support
• Raw streams (no .xz headers) for advanced users, including LZMA2 with preset dictionary

Threading is planned but it is unknown when it will be implemented.

The main source code is compatible with Java 8 and later but there are classes that are for Java 9 or later (module-info.java and speed optimizations). The default build options require OpenJDK 11 or later, and create Java 8 compatible binaries.

Building with Apache Ant

All output files go into the build directory.

• Type ant to compile the classes and create the JAR files.
• Type ant doc to build the javadoc HTML documentation.
• Type ant -projecthelp to see all available targets.

Reproducible builds

Reproducible builds should be possible. A timestamp needs to be specified which will be used for file modification times in the JAR metadata. The timestamps are stored using the local timezone, thus it's good to override it to GMT/UTC. On POSIX systems, the following commands are equivalent:

$ ANT_OPTS=-Duser.timezone=GMT \
      ant -Dant.tstamp.now.iso=2024-07-29T14:10:26Z

$ SOURCE_DATE_EPOCH=1722262226 TZ=UTC0 ant

When the Git repository is available, using the committer date is one way to get a reasonable value:

$ SOURCE_DATE_EPOCH=$(git log -n1 --pretty=%ct) TZ=UTC0 ant

Old build environments

• If you are using Ant older than 1.10.2:

  Edit build.xml and remove the modificationtime="${timestamp}" attributes from the <jar> elements.

• If you are using Ant older than 1.9.8:

  Edit build.xml and remove the release attributes from the <javac> tags, that is, remove all occurrences of these two lines:

  release="${sourcever}"
  
  release="${sourcever9}"
  

  The downside of the above is that then the -source and -target options will be used instead of --release.

• If you are using OpenJDK version older than 9:

  To build with OpenJDK 8, use -Djava8only=true on the ant command line. Then the files requiring Java >= 9 won't be built, and xz.jar won't be a modular JAR.

• If you are using OpenJDK version older than 8:

  These versions are no longer supported. Try XZ for Java 1.9 which is Java 5 compatible and only requires editing build.properties to build.

Building without Apache Ant

If you cannot or don't want to use Ant, just compile all .java files under the src directory (possibly skip the demo files src/*.java). For module support and speed optimizations (Java >= 9), compile also all .java files under the src9 directory.

Demo programs

You can test compression with XZEncDemo, which compresses from standard input to standard output:

java -jar build/jar/XZEncDemo.jar < foo.txt > foo.txt.xz

You can test decompression with XZDecDemo, which decompresses to standard output:

java -jar build/jar/XZDecDemo.jar foo.txt.xz

Contact information

• Home page: https://tukaani.org/xz/java.html
• Email: Lasse Collin [email protected]
• IRC: Larhzu on #tukaani on Libera Chat
• GitHub: https://github.com/tukaani-project/xz-java