Apache Commons Overview

Apache Commons is an Apache project that focuses on reusable Java components. Apache Commons consists of three components:
Commons Proper-A reusable Java component library.
Commons a workspace developed by the Sandbox-java component.
Commons dormant-the component library of the current inactive state.

Commons Proper is committed to creating and maintaining Java components that can be taken. These Java components are dependent on the other libraries as little as possible to make the components easy to apply. And the developers of these components do their best to keep the component interfaces stable, so that the users of the components do not have to worry about future interfaces being changed when implementing these components. The following is a list of these reusable components.

Components	Description
BCEL	Byte Code Engineering library-analyze, create, and manipulate Java class files.
Beanutils	Easy-to-use wrappers around the Java reflection and introspection APIs.
BSF	Bean Scripting Framework-interface to Scripting languages, including JSR-223
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.
Csv	Component for reading and writing comma separated value files.
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.
Functor	A functor is a function which can be manipulated as an object, or an object representing a, generic function.
Imaging	A Pure-java Image Library.
Io	Collection of I/O utilities.
Jci	Java Compiler Interface
Jcs	Java Caching System
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.
OGNL	An object-graph Navigation Language
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.
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.
Weaver	Provides an easy-to-enhance (weave) compiled bytecode.

Apache Commons Overview