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Apache Tomcat is an open source software that implements Java Servlet and Java Server Pages technologies. Different versions of Servlet and JSP specifications can use different versions of Apache Tomcat. The corresponding relationship between Tomcat and JDK version is:

Servlet specification JSP specification EL specification WebSocket specification JASPIC specification Java version supported by the latest release version 4.02.33.01.11.19.0.x9.0.278 and later 3.12.33.01.11.18.5.x8.5.477 and later version 3.12.33.01.1 not applicable 8.0.x (superseded) 8.0.53 (superseded) 7 and later version 3.02 .22.21.1 does not apply to 7.0.x7.0.966 and later (WebSocket 7 and later) 2.52.12.1 does not apply 6.0.x (archived) 6.0.53 (archived) 5 and later 2.42.0 does not apply 5.5.x (archived) 5.5.36 (archived) 1.4 and later 2.31.2 No 4.1.x (archived) 4.1.40 (archived) 1.3 and later 2.21.1 does not apply 3.3.x (archived) 3.3.2 (archived) 1.1 and later

These versions are described in detail below to help you determine which version is right for you. For more details on each release, see the relevant release notes.

Please note that although we provide downloads and documentation for older versions, such as Apache Tomcat 7.x, we strongly recommend that users use the latest stable version of Apache Tomcat whenever possible. We recognize that upgrading across major versions may not be easy, and there is still some support for users of older versions in the list. However, because of the community-driven support approach, the older your version, the fewer people who are interested or able to support you.

Alpha / Beta / Stable

There are three main versions of Tomcat, and the initial release of the major version usually ranges from Alpha to Beta to Stable.

The Alpha version may contain a large number of untested / missing features and / or major errors required by the specification and is not expected to run smoothly for any period of time.

The Beta version may contain some untested functionality and / or many relatively minor errors. The Beta version is not expected to run steadily.

The Stable version may contain a small number of relatively minor errors. The stable version is designed for production purposes and is expected to run stably for a longer time.

Apache Tomcat 9.x

Apache Tomcat 9.x is the current development focus. It is based on Tomcat 8.0.x and 8.5.x, and implements the Servlet 4.0 JSP 2.3 El 3.0 and JASPIC 1.1 specifications (the version required by the Java EE 8 platform). In addition, it includes the following important improvements:

Add support for HTTP / 2 (need to run on Java 9 (from Apache Tomcat 9.0.0.M18) or Tomcat Native libraries being installed) added support for TLS support for using OpenSSL for JSSE connectors (NIO and NIO2) added support for TLS virtual host (SNI)

Apache Tomcat 8.x

Apache Tomcat 8.0.x builds on top of Tomcat 7.0.x, and implements the Servlet 3.1 Magi JSP 2.3 Magi El 3.0 and WebSocket 1.1 specifications. In addition, it includes the following important improvements:

A single common resource implementation to replace multiple resource extensions provided in previous versions.

Apache Tomcat 8.5.x supports the same Servlet,JSP,EL and WebSocket specification versions as Apache Tomcat 8.0.x. In addition, it implements the JASPIC 1.1 specification.

It is derived from the Tomcat 9.0.0.M4 (alpha) milestone release in March 2016. It provides HTTP / 2 support and other features of the Tomcat 9.x code base, while being compatible with the Tomcat 8.0 runtime and specification requirements. (it was not possible to create a stable version of Tomcat 9.0 at the time, and the Java EE specification for Tomcat 9 was finalized several years later.)

Tomcat 8.5 is considered to be a substitute for Tomcat 8.0. Refer to the migration guide for guidance on migrating to Tomcat 8.5.

Apache Tomcat 8.5.x includes the following important improvements:

Added support for HTTP / 2 (requires Tomcat Native libraries) added support for TLS support for using OpenSSL for JSSE connectors (NIO and NIO2) added support for TLS virtual hosts (SNI)

The following technologies have been removed from Apache Tomcat 8.5.x:

The BIO implementation of HTTP and AJP connectors supports Comet API

Tomcat8.5 has undergone significant changes in many areas, resulting in improved performance, stability, and total cost of ownership. For more information, refer to the Apache Tomcat 8.5 change log.

Users of Tomcat 8.0 should be aware that Tomcat 8.0 has now stopped development. Users of Tomcat 8.0.x should upgrade to Tomcat 8.5.x or later.

Apache Tomcat 7.x

Apache Tomcat 7.x builds on the improvements of Tomcat 6.0.x and implements the Servlet 3.0, JSP 2.2 El 2.2 and WebSocket 1.1 specifications. In addition, it includes the following improvements:

Memory leak detection and prevention for Web applications improve security for Manager and Host Manager applications generic CSRF protection support includes external content refactoring (connectors, lifecycle) and extensive internal code cleanup directly in Web applications

Apache Tomcat 6.x

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

Memory usage optimization advanced IO function refactoring cluster

Users of Tomcat 6 should know that Tomcat 6 has now stopped development. Users of Tomcat 6.x should upgrade to Tomcat 7.x or later.

The above is the whole content of this article, I hope it will be helpful to your study, and I also hope that you will support it.

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