Welcome to the Apache Commons

The Commons is an Apache project focused on all aspects of reusable Java components.

The Apache Commons project is composed of three parts:

You may also read our charter, which spells out the goals of the project in greater detail.

The Commons Proper

The Commons Proper is dedicated to one principal goal: creating and maintaining reusable Java components. The Commons Proper is a place for collaboration and sharing, where developers from throughout the Apache community can work together on projects to be shared by the Apache projects and Apache users.

Commons developers will make an effort to ensure that their components have minimal dependencies on other libraries, so that these components can be deployed easily. In addition, Commons components will keep their interfaces as stable as possible, so that Apache users (including other Apache projects) can implement these components without having to worry about changes in the future.

This article gives an overview of (some of) the components which can be found here.

We welcome participation from all that are interested, at all skill levels. Coding, documentation and testing are all critical parts of the software development process. If you are interested in participating in any of these aspects, please join us!

Components
Attributes Runtime API to metadata attributes such as doclet tags.
BeanUtils Easy-to-use wrappers around the Java reflection and introspection APIs.
Betwixt Services for mapping JavaBeans to XML documents, and vice versa.
Chain "Chain of Responsibility" pattern implemention.
CLI Command Line arguments parser.
Codec General encoding/decoding algorithms (for example phonetic, base64, URL).
Collections Extends or augments the Java Collections Framework.
Compress Defines an API for working with tar, zip and bzip2 files.
Configuration Reading of configuration/preferences files in various formats.
Daemon Alternative invocation mechanism for unix-daemon-like java code.
DBCP Database connection pooling services.
DbUtils JDBC helper library.
Digester XML-to-Java-object mapping utility.
Discovery Tools for locating resources by mapping service/reference names to resource names.
EL Interpreter for the Expression Language defined by the JSP 2.0 specification.
Email Library for sending e-mail from Java.
Exec API for dealing with external process execution and environment management in Java.
FileUpload File upload capability for your servlets and web applications.
IO Collection of I/O utilities.
JCI Java Compiler Interface
Jelly XML based scripting and processing engine.
Jexl Expression language which extends the Expression Language of the JSTL.
JXPath Utilities for manipulating Java Beans using the XPath syntax.
Lang Provides extra functionality for classes in java.lang.
Launcher Cross platform Java application launcher.
Logging Wrapper around a variety of logging API implementations.
Math Lightweight, self-contained mathematics and statistics components.
Modeler Mechanisms to create Model MBeans compatible with JMX specification.
Net Collection of network utilities and protocol implementations.
Pool Generic object pooling component.
Primitives Smaller, faster and easier to work with types supporting Java primitive types.
Proxy Library for creating dynamic proxies.
SCXML An implementation of the State Chart XML specification aimed at creating and maintaining a Java SCXML engine. It is capable of executing a state machine defined using a SCXML document, and abstracts out the environment interfaces.
Transaction Implementations for multi level locks, transactional collections and transactional file access.
Validator Framework to define validators and validation rules in an xml file.
VFS Virtual File System component for treating files, FTP, SMB, ZIP and such like as a single logical file system.

The Commons Sandbox

This project also contains a workspace that is open to all Apache committers. It's a place to try out new ideas and prepare for inclusion into the Commons portion of the project or into another Apache project. Users are free to experiment with the components developed in the sandbox, but sandbox components will not necessarily be maintained, particularly in their current state.

Sandbox
CLI2 Redesign of Commons CLI.
CSV Component for reading and writing comma separated value files.
Finder Java library inspired by the UNIX find command.
Flatfile Java library for working with flat data structures.
Functor A functor is a function that can be manipulated as an object, or an object representing a single, generic function.
I18n Adds the feature of localized message bundles that consist of one or many localized texts that belong together. Think of an error message that consists of title, text, summary and error details.
Id Id is a component used to generate identifiers.
Javaflow Continuation implementation to capture the state of the application.
JNet JNet allows to use dynamically register url stream handlers through the java.net API.
Monitoring Monitoring provides a simple, lightweight toolkit to instrument java application monitoring capabilities, including performances and thread concurrency.
Nabla Nabla provides automatic differentiation classes that can generate derivative of any function implemented in the Java language.
OpenPGP Interface to signing and verifying data using OpenPGP.
Performance A small framework for microbenchmark clients, with implementations for Commons DBCP and Pool.
Pipeline Provides a set of pipeline utilities designed around work queues that run in parallel to sequentially process data objects data objects.

The Commons Dormant

These are Commons Sandbox components that have been deemed inactive since they have seen little recent development activity. If you wish to use any of these components, you must build them yourselves. It is best to assume that these components will not be released in the near future.

Dormant
Cache Cache provides object caching services.
Clazz Clazz focuses on introspection and class manipulation.
Contract This component makes all the nice features available to the java programming language that come along with contract based programming.
Convert Commons-Convert aims to provide a single library dedicated to the task of converting an object of one type to another.
Events Commons-Events provides additional classes for firing and handling events. It focusses on the Java Collections Framework, providing decorators to other collections that fire events.
Feedparser A Java RSS/Atom parser designed to elegantly support all versions of RSS (0.9, 0.91, 0.92, 1.0, and 2.0), Atom 0.5 (and future versions) as well as easy ad hoc extension and RSS 1.0 modules capability.
JJar Jakarta JAR Archive Repository
Latka Commons-Latka is an HTTP functional testing suite for automated QA, acceptance and regression testing.
Mapper Mapper is a thin abstraction layer around a project's chosen data mapping technology (a.k.a. DAO pattern).
Messenger Messenger is an easy to use and lightweight framework for working with JMS in the web tier.
Resources Resources provides a lightweight framework for defining and looking up internationalized message strings keyed by a java.util.Locale and a message key.
Scaffold Scaffold is a toolkit for building web applications.
ThreadPool ThreadPool is a simple component for asynchronously dispatching work to another thread in a pool for simple multi threaded programming.
Workflow Workflow provides a framework for building workflow management systems.
XMLIO Simple and fast importer for XML configuration or import files.

Where do I get releases?

The individual components have independent releases. Some releases for some components may be available only through the mirroring system. Some releases for some components (typically the older ones) are not available through the mirroring system.

See the individual websites listed above for the specific downloads, or use the Releases menu option.

Where do I get nightly snapshots?

Nightly snapshots of the Commons SVN can be found here.

These are meant to provide easy access to the actual project SVN tree. As this is our live development workspace, there are no guarantees as to what you will find there, although we do our best to maintain a buildable source tree.

How do I contribute, give feedback, fix bugs and so on?

The Commons project really needs and appreciates any contributions, including documentation help, source code and feedback.

Related Components @Apache

Some other Apache Projects also have commons subprojects.

So, if you can't find what you need here, you might like to take a look there. Some components which started out here have migrated to these other places.