在Java社区，有那么一小撮人，觉得Java API还不足用，至少还不够好用，就起了给增强Java API的念头，于是Apache Commons项目诞生了。为了便于被使用，Apache Commons项目采用了与Java API的包一致的方式组织，于是出现了一系列子项目。
伴随着Apache Commons项目的发展，有些子项目保持了顽强的生命力，而有些则慢慢沦为弃子，还有些新的子项目不断产生。于是，Apache Commons项目首先被分为如下3个独立的组件库：
- Apache Commons Sandbox，Java组件开发的试验空间
- Apache Commons Dormant，遗留Java组件库（不建议使用）
- Apache Commons Proper，Java组件库
事实上，大家开发过程中，通常能够想起来的都属于Apache Commons Proper库，这也是我们后续要讨论的库。所以，默认提到Apache Commons项目都是指Apache Commons Proper库中的组件。
Apache Commons Proper库中的组件都是以子项目的形式组织，列表如下：
| Components | Description | Latest Version | Released |
|---|---|---|---|
| BCEL | Byte Code Engineering Library - analyze, create, and manipulate Java class files | 6.2 | 2017-11-08 |
| BeanUtils | Easy-to-use wrappers around the Java reflection and introspection APIs. 为Java Bean的动态属性（运行时才确定的属性）提供getter/setter方法。 主要工具类：PropertyUtils（推荐），BeanUtils |
1.9.3 | 2016-09-26 |
| BSF | Bean Scripting Framework - interface to scripting languages, including JSR-223 | 3.1 | 2010-06-24 |
| Chain | Chain of Responsibility pattern implemention. | 1.2 | 2008-06-02 |
| CLI | Command Line arguments parser. | 1.4 | 2017-03-09 |
| Codec | General encoding/decoding algorithms (for example phonetic, base64, URL). | 1.11 | 2017-10-20 |
| Collections | Extends or augments the Java Collections Framework. | 4.1 | 2015-11-27 |
| Compress | Defines an API for working with tar, zip and bzip2 files. | 1.17 | 2018-06-03 |
| Configuration | Reading of configuration/preferences files in various formats. | 2.2 | 2017-10-12 |
| Crypto | A cryptographic library optimized with AES-NI wrapping Openssl or JCE algorithm implementations. | 1.0.0 | 2016-07-22 |
| CSV | Component for reading and writing comma separated value files. | 1.5 | 2017-09-03 |
| Daemon | Alternative invocation mechanism for unix-daemon-like java code. | 1.0.15 | 2013-04-03 |
| DBCP | Database connection pooling services. | 2.3.0 | 2018-05-12 |
| DbUtils | JDBC helper library. | 1.7 | 2017-07-20 |
| Digester | XML-to-Java-object mapping utility. | 3.2 | 2011-12-13 |
| Library for sending e-mail from Java. | 1.5 | 2017-08-01 | |
| Exec | API for dealing with external process execution and environment management in Java. | 1.3 | 2014-11-06 |
| FileUpload | File upload capability for your servlets and web applications. | 1.3.3 | 2017-06-13 |
| Functor | A functor is a function that can be manipulated as an object, or an object representing a single, generic function. | 1.0 | 2011-??-?? |
| Geometry | Space and coordinates. | 1.0 | 2018-??-?? |
| Imaging (previously called Sanselan) | A pure-Java image library. | 0.97-incubator | 2009-02-20 |
| IO | Collection of I/O utilities. | 2.6 | 2017-10-15 |
| JCI | Java Compiler Interface | 1.1 | 2013-10-14 |
| JCS | Java Caching System | 2.2 | 2017-08-02 |
| Jelly | XML based scripting and processing engine. | 1.0.1 | 2017-09-27 |
| Jexl | Expression language which extends the Expression Language of the JSTL. | 3.1 | 2017-04-14 |
| JXPath | Utilities for manipulating Java Beans using the XPath syntax. | 1.3 | 2008-08-14 |
| Lang | Provides extra functionality for classes in java.lang. Lang 3.0开始使用commons-lang3的构件名称。 主要工具类：StringUtils， ArrayUtils |
3.7 | 2017-11-08 |
| Logging | Wrapper around a variety of logging API implementations. | 1.2 | 2014-07-11 |
| Math | Lightweight, self-contained mathematics and statistics components. | 3.5 | 2015-04-17 |
| Net | Collection of network utilities and protocol implementations. | 3.6 | 2017-02-15 |
| Numbers | Number types (complex, quaternion, fraction) and utilities (arrays, combinatorics). | 1.0 | 2017-??-?? |
| OGNL | An Object-Graph Navigation Language | 4.0 | 2013-??-?? |
| Pool | Generic object pooling component. | 2.5.0 | 2017-12-19 |
| Proxy | Library for creating dynamic proxies. | 1.0 | 2008-02-28 |
| RDF | Common implementation of RDF 1.1 that could be implemented by systems on the JVM. | 0.3.0-incubating | 2016-11-15 |
| RNG | Implementations of random numbers generators. | 1.0 | 2016-12-13 |
| 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. |
0.9 | 2008-12-01 |
| Statistics | Statistics. | 0.1 | ????-??-?? |
| Text | Apache Commons Text is a library focused on algorithms working on strings. 处理文本（非字符串） |
1.3 | 2018-03-21 |
| Validator | Framework to define validators and validation rules in an xml file. | 1.6 | 2017-02-21 |
| VFS | Virtual File System component for treating files, FTP, SMB, ZIP and such like as a single logical file system. | 2.2 | 2017-10-06 |
| Weaver | Provides an easy way to enhance (weave) compiled bytecode. | 1.3 | 2016-10-18 |
参考链接：
http://commons.apache.org/