转自：http://blog.knowsky.com/260578.htm
问题出现：
严重: Exception starting filter struts2
java.lang.ClassNotFoundException: prg.apache.struts2.dispatcher.FilterDispatcher
at org.apache.catalina.loader.WebappClassLoader.loadClass(WebappClassLoader.java:1666)
at org.apache.catalina.loader.WebappClassLoader.loadClass(WebappClassLoader.java:1511)
at org.apache.catalina.core.DefaultInstanceManager.loadClass(DefaultInstanceManager.java:406)
at org.apache.catalina.core.DefaultInstanceManager.loadClassMaybePrivileged(DefaultInstanceManager.java:388)
at org.apache.catalina.core.DefaultInstanceManager.newInstance(DefaultInstanceManager.java:117)
at org.apache.catalina.core.ApplicationFilterConfig.getFilter(ApplicationFilterConfig.java:248)
at org.apache.catalina.core.ApplicationFilterConfig.setFilterDef(ApplicationFilterConfig.java:368)
at org.apache.catalina.core.ApplicationFilterConfig.<init>(ApplicationFilterConfig.java:98)
at org.apache.catalina.core.StandardContext.filterStart(StandardContext.java:4193)
at org.apache.catalina.core.StandardContext.startInternal(StandardContext.java:4801)
at org.apache.catalina.util.LifecycleBase.start(LifecycleBase.java:139)
at org.apache.catalina.core.ContainerBase.startInternal(ContainerBase.java:988)
at org.apache.catalina.core.StandardHost.startInternal(StandardHost.java:771)
at org.apache.catalina.util.LifecycleBase.start(LifecycleBase.java:139)
at org.apache.catalina.core.ContainerBase.startInternal(ContainerBase.java:988)
at org.apache.catalina.core.StandardEngine.startInternal(StandardEngine.java:275)
at org.apache.catalina.util.LifecycleBase.start(LifecycleBase.java:139)
at org.apache.catalina.core.StandardService.startInternal(StandardService.java:427)
at org.apache.catalina.util.LifecycleBase.start(LifecycleBase.java:139)
at org.apache.catalina.core.StandardServer.startInternal(StandardServer.java:649)
at org.apache.catalina.util.LifecycleBase.start(LifecycleBase.java:139)
at org.apache.catalina.startup.Catalina.start(Catalina.java:585)
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(Unknown Source)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(Unknown Source)
at java.lang.reflect.Method.invoke(Unknown Source)
at org.apache.catalina.startup.Bootstrap.start(Bootstrap.java:288)
at org.apache.catalina.startup.Bootstrap.main(Bootstrap.java:415)
2010-12-1 13:10:06 org.apache.catalina.core.StandardContext startInternal
严重: Error filterStart
2010-12-1 13:10:06 org.apache.catalina.core.StandardContext startInternal
严重: Context [/struts2] startup failed due to previous errors
解决方法：
很明显的错误：java.lang.ClassNotFoundException: FilterDispatcher
找不到FilterDispatcher这个类（FilterDispatcher分发器，是Struts2框架的核心Dispatcher，没有它，也就谈不起Struts2框架）
首先：看看有没有导入Struts2相应的jar包，是否齐全。最少要导入五个基本包:
commons-logging-api-1.1.jar
freemarker-2.3.8.jar
ognl-2.6.11.jar
struts2-core-2.0.12.jar
xwork-2.0.6.jar
如果该包含的jar包都引入了，再看，配置文件web.xml是否配置正确，
struts2使用的是Filter充当Control 需要配置web.xml如下：注意类名和包名不要写错
<filter>
<filter-name>struts2</filter-name>
<filter-class>org.apache.struts2.dispatcher.FilterDispatcher</filter-class>
</filter>
<filter-mapping>
<filter-name>struts2</filter-name>
<url-pattern>*.do</url-pattern>
<!-- 这里的url-pattern视你的具体情况而定-->
</filter-mapping>
<filter-mapping>
<filter-name>struts2</filter-name>
<url-pattern>/struts/*</url-pattern>
</filter-mapping>
如果以上两步都没有问题，那估计就是环境问题了，在开发中，环境问题是麻烦的事，检查你用的部署服务器（Tomcat或weblogic等）、IDE的版本（eclipse或者myEclipse），以及Struts2的版本...
struts2项目中web.xml配置2.1与2.0的区别
具体的过滤器类变了，2.0配置是以上写法
2.1以后是这样配置
<filter>
<filter-name>struts2</filter-name>
<filter-class>
org.apache.struts2.dispatcher.ng.filter.StrutsPrepareFilter
</filter-class>
</filter>
<filter-mapping>
<filter-name>struts2</filter-name>
<url-pattern>/*</url-pattern>
</filter-mapping>
另外，也与你导入jar包的位置有关，建议最好放入工程WEB-INF下的lib目录的根目录里，否则有时不能识别。
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