Apache commons-a general toolkit project under Apache

Apache commons is an open-source project under Apache. It contains many open-source tools to solve common programming problems and reduce repetitive work.

This is the official Apache Commons website.

The following is a brief introduction to the tool:

Components
Attributes	Runtime API to metadata attributes such as doclet tags.
Bcel	Byte Code Engineering Library-analyze, create, and manipulate Java class files
Beanutils	For Java Bean tool sets, bean is encapsulated to facilitate bean operations. For details about Java Bean, see here.
Betwixt	Javabean is used to map Javabean to an XML file and ing the XML file back to JavaBean.
Chain	Chain of responsibilityPattern implemention.
CLI	Tool used to parse command line parameters
Codec	Used for encoding and decoding, including base64, URL, soundx, etc.
Collections	Java collections class extension. collections is a class under the java. util package, including operations on the Collection
Mpress	Defines an API for working with tar, zip and Bzip2 files.
Configuration	It is used to process configuration files and supports multiple storage methods (propertities, XML, plist, JDBC, and so on)
Daemon	Alternative invocation mechanic for Unix-Daemon-like Java code.
DBCP	Database Connection Pooling services.
Dbutils	Simplify JDBC database operations
Digester	Ing between XML and Java objects
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	Email sending Method
Exec	API for dealing with external process execution and environment management in Java.
Fileupload	File upload capability for your servlets and Web applications.
Io	Io method set, which can be seen as Java. Io package Extension
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	Use the XPath method to view JavaBean. For more information about XPath, see here.
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.
Sanselan	A pure-Java Image Library.
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 merge acts 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.

 

PS: The httpclient component in the Commons project has now become part of Apache httpcomponents

 

Refer:

Http://commons.apache.org/index.html

Http://www.cnblogs.com/jackyrong/archive/2006/10/15/529599.html

Http://www.360doc.com/content/09/1209/16/203871_10726760.shtml