Commons下很多组件都很有用，也许你会发现辛辛苦苦写了半天的东西在这里面就有了！比如DBCP，BeanUtils，Mail和FileUpload等等。
地址:http://jakarta.apache.org/commonsComponents
Attributes Attributes provides a runtime API to metadata attributes such as doclet tags, inspired by the Nanning and XRAI projects as well as JSR 175 and C# attrbutes.
BeanUtils Commons-BeanUtils provides easy-to-use wrappers around the Java reflection and introspection APIs.
Betwixt Betwixt provides services for mapping JavaBeans to XML documents, and vice versa.
Chain Chain provides a "Chain of Responsibility" pattern implemention for organizing complex processing flows.
CLI CLI provides a simple API for working with Comamnd Line arguments, options, option groups, mandatory options and so forth.
Codec Codec contains some general encoding/decoding algorithms. Includes some phonetic encoders, Hex, Base64, and a URL encoder.
Collections Commons-Collections provides a suite of classes that extend or augment the Java Collections Framework.
Configuration Commons-Configuration Tools to assist in the reading of configuration/preferences files in various formats.
Daemon An alternative invocation mechanism for unix-daemon-like java code.
DBCP Commons-DBCP provides database connection pooling services.
DbUtils DbUtils is a JDBC helper library that factors out mundane resource cleanup code for common database tasks.
Digester Commons-Digester is an XML-to-Java-object mapping utility commonly used for parsing XML configuration files.
Discovery Commons-Discovery provides tools for locating resources (including classes) by mapping service/reference names to resource names using a variety of schemes.
EL Commons-EL provides an interpreter for the Expression Language which is defined by the JavaServer Pages(TM) specification, version 2.0.
Email Email provides a simple library for sending e-mail from Java.
FileUpload FileUpload makes it easy to add robust, high-performance, file upload capability to your servlets and web applications.
HttpClient Commons-HttpClient provides a framework for working with the client-side of the HTTP protocol.
IO IO is a collection of I/O utilities.
Jelly Jelly is an XML based scripting and processing engine. Jelly borrows many good ideas from both JSP custom tags, Velocity, Cocoon and the scripting engine inside XDoclet. Jelly can be used from the command line, inside Ant or inside a Servlet.
Jexl Jexl is an expression language which entends the Expression Language of the JSTL by bringing in some of the lessons leaned by the Velocity community.
JXPath Commons-JXPath provides utilities for manipulating Java classes that conform to the JavaBeans naming conventions using the XPath syntax. It also supports maps, DOM and other object models.
Lang Commons-Lang provides a very common set of utility classes that provide extra functionality for classes in java.lang.
Latka Commons-Latka is an HTTP functional testing suite for automated QA, acceptance and regression testing.
Launcher The Launcher Component is designed to be a cross platform Java application launcher. Commons-launcher eliminates the need for a batch or shell script to launch a Java class. The original Java classes come from the Jakarta Tomcat 4.0 project.
Logging Commons-Logging is a wrapper around a variety of logging API implementations.
Math Math is a library of lightweight, self-contained mathematics and statistics components addressing the most common practical problems not immediately available in the Java programming language.
Modeler Commons-Modeler provides mechanisms to create Model MBeans compatible with the Java Management Extensions (JMX) specification.
Net Net is a a collection of network utilities, based on the NetComponents codebase, including FTP clients etc.
Pool Commons-Pool provides a generic object pooling interface, a toolkit for creating modular object pools and several general purpose pool implementations.
Primitives Commons-Primitives provides smaller, faster and easier to work with types supporting Java primitive types. Currently Primitives is primarily focused on collections of primitives.
Resources Resources provides a lightweight framework for defining and looking up internationalized message strings keyed by a java.util.Locale and a message key.
Transaction Commons Transaction provides implementations for multi level locks, transactional collections and transactional file access and some other utility classes commonly used in transacional Java programming.
Validator The commons-validator package provides a simple, extendable framework to define validators (validation methods) and validation rules in an xml file. There is support for internationalization of validation rules and error messages.
VFS VFS is a Virtual File System component for treating files, FTP, SMB, ZIP and such like as a single logical file system.
The Sandbox
This project also contains a workspace that is open to all Jakarta committers. It's a place to try out new ideas and prepare for inclusion into the Commons portion of the project or into another Jakarta project. Users are free to experiment with the components developed in the sandbox, but sandbox components will not necessarily be maintained, particularly in their current state.
Sandbox
Cache Cache provides object caching services.
Clazz Clazz focuses on introspection and class manipulation.
Compress Commons Compress defines an API for working with tar, zip and bzip2 files.
Contract This component makes all the nice features available to the java programming language that come along with contract based programming.
Convert Commons-Convert aims to provide a single library dedicated to the task of converting an object of one type to another.
Events Commons-Events provides additional classes for firing and handling events. It focusses on the Java Collections Framework, providing decorators to other collections that fire events.
Feedparser Generic FeedParser interface and concrete implementations for Atom, FOAF, OPML and RSS.
Functor A functor is a function that can be manipulated as an object, or an object representing a single, generic function.
I18n This component adds the feature of localized message bundles that consist of one or many localized texts that belong together. Think of an error message that consists of title, text, summary and error details.
Id Id is a component used to generate identifiers.
Javaflow Continuation implementation to capture the state of the application.
JCI Java Compiler Interface
JJar Jakarta JAR Archive Repository
Mapper Mapper is a thin abstraction layer around a project's chosen data mapping technology (a.k.a. DAO pattern).
Messenger Messenger is an easy to use and lightweight framework for working with JMS in the web tier.
Pipeline This component provides a set of pipeline utilities designed around work queues that run in parallel to sequentially process data objects data objects.
Scaffold Scaffold is a toolkit for building web applications.
SQL Commons SQL is a component for working with databases and generating DDL. It contains a simple set of beans that represent a relational database schema such as a Database, Table, Column etc.
ThreadPool ThreadPool is a simple component for asynchronously dispatching work to another thread in a pool for simple multi threaded programming.
Workflow Workflow provides a framework for building workflow management systems.
XMLIO Simple and fast importer for XML configuration or import files.