tomcat 和servlet之间的关系

http://tomcat.apache.org/whichversion.html

pache Tomcat Versions

Apache Tomcat^® is an open source software implementation of the Java Servlet and JavaServer Pages technologies. Different versions of Apache Tomcat are available for different versions of the Servlet and JSP specifications. The mapping between the specifications and the respective Apache Tomcat versions is:

Servlet Spec	JSP Spec	EL Spec	WebSocket Spec	JASPIC Spec	Apache Tomcat version	Actual release revision	Supported Java Versions
4.0	TBD (2.4?)	TBD (3.1?)	TBD (1.2?)	1.1	9.0.x	9.0.0.M13 (alpha)	8 and later
3.1	2.3	3.0	1.1	1.1	8.5.x	8.5.8	7 and later
3.1	2.3	3.0	1.1	N/A	8.0.x (superseded)	8.0.39 (superseded)	7 and later
3.0	2.2	2.2	1.1	N/A	7.0.x	7.0.73	6 and later (7 and later for WebSocket)
2.5	2.1	2.1	N/A	N/A	6.0.x	6.0.48	5 and later
2.4	2.0	N/A	N/A	N/A	5.5.x (archived)	5.5.36 (archived)	1.4 and later
2.3	1.2	N/A	N/A	N/A	4.1.x (archived)	4.1.40 (archived)	1.3 and later
2.2	1.1	N/A	N/A	N/A	3.3.x (archived)	3.3.2 (archived)	1.1 and later

Each version of Tomcat is supported for any stable Java release that meets the requirements of the final column in the table above.

Tomcat should also work on any Java early access build that meets the requirements of the final column in the table above. For example, users were successfully running Tomcat 8 on Java 8 many months before the first stable Java 8 release. However, users of early access builds should be aware of the following:

It is not unusual for the initial early access builds to contain bugs that can cause problems for web applications running on Tomcat.
If the new Java version introduces new language features then the default JSP compiler may not support them immediately. Switching the JSP compiler to javac may enable these new language features to be used in JSPs.
If you do discover an problem using a Java early access build, please ask for help. The Tomcat user's mailing list is probably the best place to start.

The releases are described in more detail below to help you determine which one is right for you. More details about each release can be found in the associated release notes.

Please note that although we offer downloads and documentation of older releases, such as Apache Tomcat 6.x, we strongly encourage users to use the latest stable version of Apache Tomcat whenever possible. We recognize that upgrading across major versions may not be a trivial task, and some support is still offered on the mailing list for users of old versions. However, because of the community-driven support approach, the older your version, fewer people will be interested or able to support you.

Alpha / Beta / Stable

When voting for a release, reviewers specify the stability level that they consider the release has reached. Initial releases of a new major version typically process from Alpha, through Beta to Stable over a period of several months. However, the Stable level is only available once the Java specifications the release implements have been finalised. This means a release that in all other respects is considered stable, may still be labelled as Beta if the specifications are not final.

The download pages will always show the latest stable release and any newer Alpha or Beta release if one exists. Alpha and beta releases are always clearly marked on the download pages.

Stability is a subjective judgement and you should always read carefully the release notes for any version you intend to make use of. If you are an early adopter of a release, we would love to hear your opinion about its stability as part of the vote: it takes place on the development mailing list.

Alpha releases may contain large amounts of untested/missing functionality required by the specification and/or significant bugs and are not expected to run stably for any length of time.

Beta releases may contain some untested functionality and/or a number of relatively minor bugs. Beta releases are not expected to run stably.

Stable releases may contain a small number of relatively minor bugs. Stable releases are intended for production use and are expected to run stably for extended periods of time.

Apache Tomcat 9.x

Apache Tomcat 9.x is the current focus of development, it builds on Tomcat 8.0.x and implements the current draft of the Servlet 4.0 specification and will also implement the JSP 2.4?, EL 3.1? and Web Socket 1.2? specifications once work starts on updating those specifications for Java EE 8. In addition to this, it includes the following significant improvements:

Adds support for HTTP/2 (requires the APR/native library)
Adds support for TLS virtual hosting
Adds support for using OpenSSL for TLS support with the JSSE connectors (NIO and NIO2)

Apache Tomcat 8.x

Apache Tomcat 8.x builds on Tomcat 7.0.x and implements the Servlet 3.1, JSP 2.3, EL 3.0 and Web Socket 1.1 specifications. In addition to that, it includes the following significant improvements:

A single, common resources implementation to replace the multiple resource extension features provided in earlier versions.

Apache Tomcat 7.x

Apache Tomcat 7.x builds upon the improvements made in Tomcat 6.0.x and implements the Servlet 3.0, JSP 2.2, EL 2.2 and Web Socket 1.1 specifications. In addition to that, it includes the following improvements:

Web application memory leak detection and prevention
Improved security for the Manager and Host Manager applications
Generic CSRF protection
Support for including external content directly in a web application
Refactoring (connectors, lifecycle) and lots of internal code clean-up

Apache Tomcat 6.x

Apache Tomcat 6.x builds upon the improvements made in Tomcat 5.5.x and implements the Servlet 2.5 and JSP 2.1 specifications. In addition to that, it includes the following improvements:

Memory usage optimizations
Advanced IO capabilities
Refactored clustering

Users of Tomcat 6 should be aware that the Tomcat team have announced the end of life date for Tomcat 6.x. Users of Tomcat 6.x should plan to upgrade before Tomcat 6.x reaches end of life.

Apache Tomcat 5.x

Apache Tomcat 5.x is available for download from the archives.

Apache Tomcat 5.5.x supports the same Servlet and JSP Specification versions as Apache Tomcat 5.0.x. There are significant changes in many areas under the hood, resulting in improved performance, stability, and total cost of ownership. Please refer to the Apache Tomcat 5.5 Changelog for details.

Apache Tomcat 5.0.x improves on Apache Tomcat 4.1 in many ways, including:

Performance optimizations and reduced garbage collection
Refactored application deployer, with an optional standalone deployer allowing validation and compilation of a web application before putting it in production
Complete server monitoring using JMX and the manager web application
Scalability and reliability enhancements
Improved Taglibs handling, including advanced pooling and tag plugins
Improved platform integration, with native Windows and Unix wrappers
Embedding using JMX
Enhanced Security Manager support
Integrated session clustering
Expanded documentation

Apache Tomcat 4.x

Apache Tomcat 4.x is available for download from the archives.

Apache Tomcat 4.x implements a new servlet container (called Catalina) that is based on completely new architecture. The 4.x releases implement the Servlet 2.3 and JSP 1.2 specifications.

Apache Tomcat 4.1.x is a refactoring of Apache Tomcat 4.0.x, and contains significant enhancements, including:

JMX based administration features
JSP and Struts based administration web application
New Coyote connector (HTTP/1.1, AJP 1.3 and JNI support)
Rewritten Jasper JSP page compiler
Performance and memory efficiency improvements
Enhanced manager application support for integration with development tools
Custom Ant tasks to interact with the manager application directly from build.xml scripts

Apache Tomcat 4.0.x. Apache Tomcat 4.0.6 is the old production quality release. The 4.0 servlet container (Catalina) has been developed from the ground up for flexibility and performance. Version 4.0 implements the final released versions of the Servlet 2.3 and JSP 1.2 specifications. As required by the specifications, Apache Tomcat 4.0 also supports web applications built for the Servlet 2.2 and JSP 1.1 specifications with no changes.

Apache Tomcat 3.x

Apache Tomcat 3.x is available for download from the archives.

Version 3.3 is the current production quality release for the Servlet 2.2 and JSP 1.1 specifications. Apache Tomcat 3.3 is the latest continuation of the Apache Tomcat 3.x architecture; it is more advanced then 3.2.4, which is the 'old' production quality release.
Version 3.2.4 is the 'old' production quality release and is now in maintenance only mode.
Version 3.1.1 is a legacy release.

All Apache Tomcat 3.x releases trace their heritage back to the original Servlet and JSP implementations that Sun donated to the Apache Software Foundation. The 3.x versions all implement the Servlet 2.2 and JSP 1.1 specifications.

Apache Tomcat 3.3.x. Version 3.3.2 is the current production quality release. It continues the refactoring that was begun in version 3.2 and carries it to its logical conclusion. Version 3.3 provides a much more modular design and allows the servlet container to be customized by adding and removing modules that control the processing of servlet requests. This version also contains many performance improvements.

Apache Tomcat 3.2.x. Version 3.2 added few new features since 3.1; the major effort was a refactoring of the internals to improve performance and stability. The 3.2.1 release, like 3.1.1, was a security patch. Version 3.2.2 fixed a large number of bugs and all known specification compliance issues. Version 3.2.3 was a security update that closes a serious security hole. Version 3.2.4 is a minor bug fix release. All users of Apache Tomcat versions prior to 3.2.3 should upgrade as soon as possible. With the exception of fixes for critical security related bugs, development on the Apache Tomcat 3.2.x branch has stopped.

Apache Tomcat 3.1.x. The 3.1 release contained several improvements over Apache Tomcat 3.0, including servlet reloading, WAR file support and added connectors for the IIS and Netscape web servers. The latest maintenance release, 3.1.1, contained fixes for security problems. There is no active development ongoing for Apache Tomcat 3.1.x. Users of Apache Tomcat 3.1 should update to 3.1.1 to close the security holes and they are strongly encouraged to migrate to the current production release, Apache Tomcat 3.3.

Apache Tomcat 3.0.x. Initial Apache Tomcat release.