本文章作为struts2性能调优的参考文章，其中涉及内容为官方涉及内容。不准确之地邀请大家指正并共同搭建完美文档。
Performance tuning
The following are some tips and tricks to squeeze the most performance out of Struts 2.
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Important OGNL update For Struts 2 versions before 2.3: the OGNL version 3.0.3 library is a drop-in replacement for older OGNL jars, and provides much better performance. See the following Jira issue for more information: https://issues.apache.org/jira/browse/WW-3580 |
Turn off logging and devMode.
1.关闭logging and DEVMODE
devMode在struts.properties下修改：struts.devMode=false
logging在web.xml中修改：
<servlet>
<init-param>
<param-name>debug</param-name>
<param-value>0</param-value>
</init-param>
<init-param>
<param-name>detail</param-name>
<param-value>0</param-value>
</init-param>
</servlet>
devMode allows reloading of configuration and validation related files, but because they happen on each request, this setting will totally kill your performance.
When using logging, make sure to turn off logging (esp. Freemarker generates a LOT of logging), and check if a level is enabled before printing it, or you will get the cost of the String parsing/concatination anyways.
Use the Java Templates
2.使用java的模板
If you use the simple theme, and do not overwrite any of the FreeMarker templates, consider using the java templates, which provide a drop in replacement for most tags, and are a lot faster than the regular tags.
Do not use interceptors you do not need.
3.不要使用不需要的拦截器
如果一个Action不需要全栈的拦截器的话，就使用basicStack拦截器或移除不需要的拦截器。
If you do not require a full stack of interceptors for an Action, then try using a different one (basicStack), or remove interceptors you do not need. Remove the I18nInterceptor interceptor if you don't need it, as it can cause a session to be created.
Use the correct HTTP headers (Cache-Control & Expires).
4.使用正确的http头（缓存控制和过期时间）
当返回一个html页面的时候，要保证html页面包含正确的header，使得浏览器可以知道怎样缓存该html页面。
When returning HTML views, make sure to add the correct headers so browsers know how to cache them.
Copy the static content from the Struts 2 jar when using the Ajax theme (Dojo) or the Calendar tag.
5.当你使用struts2中的ajax theme（Dojo）或者日历tag的时候将其静态内容从struts2 jar中复制到http服务器
Struts 2 uses some external javascript libraries and cascading stylesheets for certain themes and tags. These by default are located inside the Struts 2 jar, and a special filter returns them when requesting a special path (/struts). Although Struts 2 can handle these requests, an application/servlet container is not optimized for these kind of requests. Consider moving these .js and .css files to a seperated server (Lighttpd, Apache HTTPD, ..).
Create a freemarker.properties file in your WEB-INF/classes directory.
6.在web-info/classes创建freemarker.propertices文件。
创建创建freemarker.propertices文件，并添加以下设置：
template_update_delay=60000
开发的时候不要修改这个参数。
Create the freemarker.properties file and add the following setting (or whatever value you deem fitting):
template_update_delay=60000
This value determines how often Freemarker checks if it needs to reloads the templates from disk. The default value is 500 ms. Since there is no reason to check if a template needs reloading, it is best to set this to a very large value. Note that this value is in seconds and freemarker will convert this value to milliseconds.
See also: Freemarker configuration properties
Enable Freemarker template caching
7启用Freemarker模板缓存
将struts.freemark.templatesCache设置为ture启用freemark的缓存，此设置默认为false
As of Struts 2.0.10, setting the property struts.freemarker.templatesCache to true will enable the Struts internal caching of Freemarker templates. This property is set to false by default.
In Struts versions prior to 2.0.10, you had to copy the /template directory from the Struts 2 jar in your WEB_APP root to utilize Freemarker's built in chaching mechanism in order to achieve similar results.
The built in Freemarker caching mechanism fails to properly cache templates when they are retrieved from the classpath. Copying them to the WEB_APP root allows Freemarker to cache them correctly. Freemarker looks at the last modified time of the template to determine if it needs to reload the templates. Resources retrieved from the classpath have no last modified time, so Freemarker will reload them on every request.
When overriding a theme, copy all necessary templates to the theme directory.
8.当覆盖一个theme时，copy所有的模板到theme目录
当template在当前目录不能发现时，会有性能开销。因为在返回父模板前，struts2必须在当前目录进行theme检查. 晚先时候,这个缺陷将要通过一个 template缓存解决。
There's a performance cost when a template cannot be found in the current directory. The reason for this is that Struts 2 must check for a template in the current theme first before falling back to the parent theme. In the future, this penalty could be eliminated by implementing a missing template cache in Struts 2.
Do not create sessions unless you need them.
9如果不需要，不要创建sessions
除非需要，Struts2不会创建sessions(比如,在你的拦截器stack中有createSession拦截器)。注意当使用SiteMesh时, 一个session将总是被创建(看看http://forums.opensymphony.com /thread.jspa?messageID=5688的描述).
Struts 2 does not create sessions unless asked to (for example, by having the createSession interceptor in your interceptor stack). Note that when you use SiteMesh however, a session will always be created (See http://forums.opensymphony.com/thread.jspa?messageID=5688 for details). The I18nInterceptor interceptor can create sessions, so make sure you remove it, if you don't need it.
When using Freemarker, try to use the Freemarker equivalent rather than using the JSP tags.
10.当使用FreeMarker时，尽量使用等价的FreeMarker元素，代替JSP的标签
Freemarker支持list迭代, 显示属性,包含其他模版, macro's等等.使用等价的FreeMarker元素代替struts2的tags 会有小的性能提升。 (例如：<s:property value="foo"/>将要被${foo}代替).
Freemarker has support for iterating lists, displaying properties, including other templates, macro's, and so on. There is a small performance cost when using the S2 tags instead of the Freemarker equivalent (eg. <s:property value="foo"/> should be replaced by ${foo}).
参考文档：performance_tuning in website struts.apache.org/2.3.1.1/docs/performance-tuning.html