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HEADS UP: As of February 1, 2016, Preon switched from a GPL license to a permissive MIT license.

HEADS UP: Preon needs a new maintainer. In fact, I pretty much haven't worked on it for years now. Meanwhile, people are considering it to be useful. However I moved on, from Java to Scala and now Node.js, and I don't see myself return to Java in a while. If you happen to be interested to take over ownership of this project, then send me an email: wilfredspringer at

Circle CI

Preon aims to provide a framework for dealing with binary encoded data; or more specifically, it aims to deal with situations in which bytes are considered to be overkill. The project is named after the "point-like" particles, conceived to be subcomponents of quarks and leptons. Let's just say very small particles that you don't see with the naked eye, but you probably rely on them without knowing.

Preon is to bitstream encoded content what JAXB is to XML, or Hibernate to relational databases. You define your in memory representation of the data structure in Java classes, and add annotations to 'tell' how it should be mapped onto a bitstream encoded representation. Preon takes care of the rest: it will give you a decoder, hyperlinked documentation on the encoding format, and - if you want - annotated hexdumps explaining you exactly what you're looking at.

Distinctive features

  • Preon does not a assume a finite set of compression algorithms. There are many ways to compress data. Preon allows compression experts to add components that from that part on become part of Preon's declarative language. Preon is extensible.
  • Preon is capable of generating documentation that would not look bad on Wikipedia.
  • Preon does not assume all data can be loaded in memory in a single go. Instead, it will pull data in on demand, only if it's needed. All logic required to understand how to jump to different parts of the file are hidden from the user.
  • Preon does not assume there will only be a single thread consuming the data.
  • Preon is declarative in nature, but the dependencies between different data elements inside an encoded representation can be modelled as complex expressions.
  • Preon was used to creata a Java bytecode parser without writing a single line of imperative code.

More documentation

A word on codehaus

Preon used to be hosted at the Codehaus. Unfortunately, the Codehaus no longer exists. You may still find reference to Codehaus in the source code. I might rename the package names of future versions to something that no longer references Codehaus.

Issue tracker, JavaDocs, etc.

The issue tracker used to be based on the one hosted by Codehaus. With that one gone, future issues will be tracked in Github.


Bit syntax for Java






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