这个是struts2的核心过滤器(Filter)，代码如下：

1 /*  2  * $Id: DefaultActionSupport.java 651946 2008-04-27 13:41:38Z apetrelli $  3  *  4  * Licensed to the Apache Software Foundation (ASF) under one  5  * or more contributor license agreements.  See the NOTICE file  6  * distributed with this work for additional information  7  * regarding copyright ownership.  The ASF licenses this file  8  * to you under the Apache License, Version 2.0 (the  9  * "License"); you may not use this file except in compliance 10  * with the License.  You may obtain a copy of the License at 11  * 12  *  http://www.apache.org/licenses/LICENSE-2.0 13  * 14  * Unless required by applicable law or agreed to in writing, 15  * software distributed under the License is distributed on an 16  * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY 17  * KIND, either express or implied.  See the License for the 18  * specific language governing permissions and limitations 19  * under the License. 20  */ 21 package org.apache.struts2.dispatcher.ng.filter; 22  23 import org.apache.struts2.StrutsStatics; 24 import org.apache.struts2.dispatcher.Dispatcher; 25 import org.apache.struts2.dispatcher.mapper.ActionMapping; 26 import org.apache.struts2.dispatcher.ng.ExecuteOperations; 27 import org.apache.struts2.dispatcher.ng.InitOperations; 28 import org.apache.struts2.dispatcher.ng.PrepareOperations; 29  30 import javax.servlet.*; 31 import javax.servlet.http.HttpServletRequest; 32 import javax.servlet.http.HttpServletResponse; 33 import java.io.IOException; 34 import java.util.List; 35 import java.util.regex.Pattern; 36  37 /** 38  * Handles both the preparation and execution phases of the Struts dispatching process.  This filter is better to use 39  * when you don't have another filter that needs access to action context information, such as Sitemesh. 40  */ 41 public class StrutsPrepareAndExecuteFilter implements StrutsStatics, Filter { 42     protected PrepareOperations prepare; 43     protected ExecuteOperations execute; 44     protected List
     
       excludedPatterns = null; 45  46     public void init(FilterConfig filterConfig) throws ServletException { 47         InitOperations init = new InitOperations(); 48         try { 49             FilterHostConfig config = new FilterHostConfig(filterConfig); 50             init.initLogging(config); 51             Dispatcher dispatcher = init.initDispatcher(config); 52             init.initStaticContentLoader(config, dispatcher); 53  54             prepare = new PrepareOperations(filterConfig.getServletContext(), dispatcher); 55             execute = new ExecuteOperations(filterConfig.getServletContext(), dispatcher); 56             this.excludedPatterns = init.buildExcludedPatternsList(dispatcher); 57  58             postInit(dispatcher, filterConfig); 59         } finally { 60             init.cleanup(); 61         } 62  63     } 64  65     /** 66      * Callback for post initialization 67      */ 68     protected void postInit(Dispatcher dispatcher, FilterConfig filterConfig) { 69     } 70  71     public void doFilter(ServletRequest req, ServletResponse res, FilterChain chain) throws IOException, ServletException { 72  73         HttpServletRequest request = (HttpServletRequest) req; 74         HttpServletResponse response = (HttpServletResponse) res; 75  76         try { 77             prepare.setEncodingAndLocale(request, response); 78             prepare.createActionContext(request, response); 79             prepare.assignDispatcherToThread(); 80             if ( excludedPatterns != null && prepare.isUrlExcluded(request, excludedPatterns)) { 81                 chain.doFilter(request, response); 82             } else { 83                 request = prepare.wrapRequest(request); 84                 ActionMapping mapping = prepare.findActionMapping(request, response, true); 85                 if (mapping == null) { 86                     boolean handled = execute.executeStaticResourceRequest(request, response); 87                     if (!handled) { 88                         chain.doFilter(request, response); 89                     } 90                 } else { 91                     execute.executeAction(request, response, mapping); 92                 } 93             } 94         } finally { 95             prepare.cleanupRequest(request); 96         } 97     } 98  99     public void destroy() {100         prepare.cleanupDispatcher();101     }102 }
     

doFilter方法的作用是捕获以.action为结尾的请求，然后给他分配action，处理request，返回response！