Apache Commons是Apache旗下的一个开源项目，包含了很多开源的工具，用于解决平时编程经常会遇到的问题，减少重复劳动
这里是Apache commons的官方网站
下面是工具的简单介绍：
| Components | |
|---|---|
| Attributes | Runtime API to metadata attributes such as doclet tags. |
| BCEL | Byte Code Engineering Library - analyze, create, and manipulate Java class files |
| BeanUtils | 针对java bean的工具集，对bean进行了很多包装，可以方便地对bean进行操作，有关java bean的情况参看这里 |
| Betwixt | 用来将javabean映射为xml文件以及将xml文件映射回javabean |
| Chain | Chain of Responsibility pattern implemention. |
| CLI | 用于解析命令行参数的工具 |
| Codec | 用来编码和解码，包括Base64，URL，Soundx等等 |
| Collections | Java Collections类的拓展， collections是java.util包下的一个类，包括有关集合的操作 |
| mpress | Defines an API for working with tar, zip and bzip2 files. |
| Configuration | 用来帮助处理配置文件，支持多种存储方式（propertities,xml,plist,JDBC等等） |
| Daemon | Alternative invocation mechanism for unix-daemon-like java code. |
| DBCP | Database connection pooling services. |
| DbUtils | 简化JDBC的数据库操作 |
| Digester | xml和java对象间的映射 |
| 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. |
| 发送email的方法 | |
| 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方法的集合，可以看为java.io包的扩展 |
| 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 | 用XPath的方法查看javabean，有关XPath的情况看这里 |
| 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 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. |
ps:原来在commons项目中的httpclient组件现在变为 Apache HttpComponents的一部分
参考：
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