Apache Commons 是一个关注于可复用的 Java 组件的 Apache 项目。Apache Commons 由三部分构成：
Commons Proper - 一个可复用的 Java 组件库。
Commons Sandbox - Java 组件开发的工作区。
Commons Dormant - 当前非活动状态的组件库。
Commons Proper 致力于创建和维护可服用的 Java 组件。这些 Java 组件都是尽可能小地依赖其他的库使得组件能够方便地应用。而且这些组件的开发者尽力地保持组件接口的稳定，这样组件的使用者在实现这些组件的时候就不必担心未来接口会发生变化。以下是这些可复用组件的列表。
| 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. |
| 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 that can be manipulated as an object, or an object representing a single, 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 way to enhance (weave) compiled bytecode. |