Tomcat是Apache 软件基金会(Apache Software Foundation)的Jakarta 项目中的一个核心项目，由Apache、Sun 和其他一些公司及个人共同开发而成。由于有了Sun 的参与和支持，最新的Servlet 和JSP 规范总是能在Tomcat 中得到体现，因为Tomcat 技术先进、性能稳定,而且免费，因而深受Java 爱好者的喜爱并得到了部分软件开发商的认可，成为目前比较流行的Web 应用服务器。Tomcat 很受广大程序员的喜欢，因为它运行时占用的系统资源小，扩展性好，支持负载平衡与邮件服务等开发应用系统常用的功能；而且它还在不断的改进和完善中，任何一个感兴趣的程序员都可以更改它或在其中加入新的功能。

下载:Tomcat 6.0.20

http://people.apache.org/~remm/tomcat-6/v6.0.20/bin/
　　Apache Tomcat Version 6.0.20
　　Release Notes

=============================
　　KNOWN ISSUES IN THIS RELEASE:
　　=============================

* Dependency Changes
　　* JNI Based Applications
　　* Bundled APIs
　　* Web application reloading and static fields in shared libraries
　　* Tomcat on Linux
　　* Enabling SSI and CGI Support
　　* Security manager URLs
　　* Symlinking static resources
　　* Enabling invoker servlet
　　* Viewing the Tomcat Change Log
　　* When all else fails

===================
　　Dependency Changes:
　　===================

Tomcat 6.0 is designed to run on JSE 5.0 and later.
　　In addition, Tomcat 6.0 uses the Eclipse JDT Java compiler for compiling
　　JSP pages. This means you no longer need to have the complete
　　Java Development Kit (JDK) to run Tomcat, but a Java Runtime Environment
　　(JRE) is sufficient. The Eclipse JDT Java compiler is bundled with the
　　binary Tomcat distributions. Tomcat can also be configured to use the
　　compiler from the JDK to compile JSPs, or any other Java compiler supported
　　by Apache Ant.

=======================
　　JNI Based Applications:
　　=======================

Applications that require native libraries must ensure that the libraries have
　　been loaded prior to use. Typically, this is done with a call like:
　　static {
　　System.loadLibrary("path-to-library-file");
  　}
　　in some class. However, the application must also ensure that the library is
　　not loaded more than once. If the above code were placed in a class inside
　　the web application (i.e. under /WEB-INF/classes or /WEB-INF/lib), and the
　　application were reloaded, the loadLibrary() call would be attempted a second time.
　　To avoid this problem, place classes that load native libraries outside of the
　　web application, and ensure that the loadLibrary() call is executed only once
　　during the lifetime of a particular JVM.

=============
　　Bundled APIs:
　　=============

A standard installation of Tomcat 6.0 makes all of the following APIs available
　　for use by web applications (by placing them in "lib"):

* annotations-api.jar (Annotations package)
　　* catalina.jar (Tomcat Catalina implementation)
　　* catalina-ant.jar (Tomcat Catalina Ant tasks)
　　* catalina-ha.jar (High availability package)
　　* catalina-tribes.jar (Group communication)
　　* el-api.jar (EL 2.1 API)
  　* jasper.jar (Jasper 2 Compiler and Runtime)
　　* jasper-el.jar (Jasper 2 EL implementation)
　　* jasper-jdt.jar (Eclipse JDT 3.3 Java compiler)
　　* jsp-api.jar (JSP 2.1 API)
  　* servlet-api.jar (Servlet 2.5 API)
　　* tomcat-coyote.jar (Tomcat connectors and utility classes)
　　* tomcat-dbcp.jar (package renamed database connection pool based on Commons DBCP)

You can make additional APIs available to all of your web applications by
　　putting unpacked classes into a "classes" directory (not created by default),
　　or by placing them in JAR files in the "lib" directory.
　　To override the XML parser implementation or interfaces, use the endorsed
　　mechanism of the JVM. The default configuration defines JARs located in
　　"endorsed" as endorsed.
　　Web application reloading and static fields in shared libraries:

================================================================
　　Some shared libraries (many are part of the JDK) keep references to objects
　　instantiated by the web application. To avoid class loading related problems
　　(ClassCastExceptions, messages indicating that the classloader
　　is stopped, etc.), the shared libraries state should be reinitialized.
　　Something which might help is to avoid putting classes which would be
  　referenced by a shared static field in the web application classloader,
　　and putting them in the shared classloader instead (JARs should be put in the
　　"lib" folder, and classes should be put in the "classes" folder).