StrutsPrepareAndExecuteFilter的作用及应用
概要说明 FilterDispatcher是早期struts2的过滤器，后期的都用StrutsPrepareAndExecuteFilter了，如 2.1.6、2.1.8。StrutsPrepareAndExecuteFilter名字已经很能说明问题了，prepare与execute，前者表示准备，可以说是指filter中的init方法，即配制的导入；后者表示进行过滤，指doFilter方法，即将request请求，转发给对应的 action去处理。FilterDispatcher是struts2.0.x到2.1.2版本的核心过滤器.!StrutsPrepareAndExecuteFilter的优势 StrutsPrepareAndExecuteFilter是自2.1.3开始就替代了FilterDispatcher的,这样的改革当然是有好处的.!为什么这么说.? 应该知道如果我们自己定义过滤器的话, 是要放在strtus2的过滤器之前的, 如果放在struts2过滤器之后,你自己的过滤器对action的过滤作用就废了,不会有效!除非你是访问jsp/html! 那我现在有需求, 我必须使用Action的环境,而又想在执行action之前拿filter做一些事, 用FilterDispatcher是做不到的.!那么StrutsPrepareAndExecuteFilter可以把他拆分成StrutsPrepareFilter和StrutsExecuteFilter,可以在这两个过滤器之间加上我们自己的过滤器.!给你打个比喻, 现在有病人要做手术, 现在struts2要做两件事, 搭病床(环境),执行手术.! 那么打麻药的工作呢.? 不可能要病人站着打吧, 所以必须有病床的环境,打完麻药之后再动手术.! 这个比喻非常形象了.! 如果是2.1.3之前的版本，用org.apache.struts2.dispatcher.FilterDispatcher，否则，用org.apache.struts2.dispatcher.ng.filter.StrutsPrepareAndExecuteFilter。 从Struts2.1.3开始，将废弃ActionContextCleanUp过滤器，而在StrutsPrepareAndExecuteFilter过滤器中包含相应的功能。一、概述 Struts2的核心是一个Filter，Action可以脱离web容器，那么是什么让http请求和action关联在一起的，下面我们深入源码来分析下Struts2是如何工作的。FilterDispatcher API 写道Deprecated. Since Struts 2.1.3, use StrutsPrepareAndExecuteFilter instead or StrutsPrepareFilter and StrutsExecuteFilter if needing using the ActionContextCleanUp filter in addition to this one 鉴于常规情况官方推荐使用StrutsPrepareAndExecuteFilter替代FilterDispatcher，我们此文 将剖析StrutsPrepareAndExecuteFilter，其在工程中作为一个Filter配置在web.xml中，配置如下：Xml代码 struts2 filter-name > org.apache.struts2.dispatcher.ng.filter.StrutsPrepareAndExecuteFilter filter-class > filter > struts2 filter-name > /* url-pattern > filter-mapping > [xml] view plaincopy<filter><filter-name>struts2</filter-name><filter-class>org.apache.struts2.dispatcher.ng.filter.StrutsPrepareAndExecuteFilter</filter-class></filter><filter-mapping><filter-name>struts2</filter-name><url-pattern>/*</url-pattern></filter-mapping> 二、源码属性方法简介 下面我们研究下StrutsPrepareAndExecuteFilter源码，类的主要信息如下： 属性摘要protected List <pattern>excludedPatterns protected ExecuteOperationsexecute protected PrepareOperationsprepare StrutsPrepareAndExecuteFilter与普通的Filter并无区别，方法除继承自Filter外，仅有一个回调方法，第三部分我 们将按照Filter方法调用顺序，由init—>doFilter—>destroy顺序地分析源码。方法摘要 voiddestroy () 继承自Filter，用于资源释放 voiddoFilter (ServletRequest req, ServletResponse res, FilterChain chain) 继承自Filter，执行方法 voidinit (FilterConfig filterConfig) 继承自Filter，初始化参数protected voidpostInit (Dispatcher dispatcher, FilterConfig filterConfig) Callback for post initialization（一个空的方法，用于方法回调初始化） 三、源码剖析 1、init方法 init是Filter第一个运行的方法，我们看下struts2的核心Filter在调用init方法初始化时做哪些工作：Java代码 public void init(FilterConfig filterConfig) throws ServletException { InitOperations init = new InitOperations(); try { //封装filterConfig，其中有个主要方法getInitParameterNames将参数名字以String格式存储在List中 FilterHostConfig config = new FilterHostConfig(filterConfig); // 初始化struts内部日志 init.initLogging(config); //<strong>创建dispatcher ，并初始化，这部分下面我们重点分析，初始化时加载那些资源</strong> Dispatcher dispatcher = init.initDispatcher(config); init.initStaticContentLoader(config, dispatcher); //初始化类属性：prepare 、execute prepare = new PrepareOperations(filterConfig.getServletContext(), dispatcher); execute = new ExecuteOperations(filterConfig.getServletContext(), dispatcher); this .excludedPatterns = init.buildExcludedPatternsList(dispatcher); //回调空的postInit方法 postInit(dispatcher, filterConfig); } finally { init.cleanup(); } } [java] view plaincopy public void init(FilterConfig filterConfig) throws ServletException { InitOperations init = new InitOperations(); try { //封装filterConfig，其中有个主要方法getInitParameterNames将参数名字以String格式存储在List中 FilterHostConfig config = new FilterHostConfig(filterConfig); // 初始化struts内部日志 init.initLogging(config); //<strong>创建dispatcher ，并初始化，这部分下面我们重点分析，初始化时加载那些资源</strong> Dispatcher dispatcher = init.initDispatcher(config); init.initStaticContentLoader(config, dispatcher); //初始化类属性：prepare 、execute prepare = new PrepareOperations(filterConfig.getServletContext(), dispatcher); execute = new ExecuteOperations(filterConfig.getServletContext(), dispatcher); this.excludedPatterns = init.buildExcludedPatternsList(dispatcher); //回调空的postInit方法 postInit(dispatcher, filterConfig); } finally { init.cleanup(); } } 首先看下FilterHostConfig ，源码如下： Java代码 public class FilterHostConfig implements HostConfig { private FilterConfig config; /** *构造函数 */ public FilterHostConfig(FilterConfig config) { this .config = config; } /** * 根据init-param配置的param-name获取param-value的值 */ public String getInitParameter(String key) { return config.getInitParameter(key); } /** * 返回初始化参数名的List */ public Iterator<string> getInitParameterNames() { return MakeIterator.convert(config.getInitParameterNames()); } public ServletContext getServletContext() { return config.getServletContext(); } } [java] view plaincopypublic class FilterHostConfig implements HostConfig { private FilterConfig config; /** *构造函数 */ public FilterHostConfig(FilterConfig config) { this.config = config; } /** * 根据init-param配置的param-name获取param-value的值 */ public String getInitParameter(String key) { return config.getInitParameter(key); } /** * 返回初始化参数名的List */ public Iterator<string> getInitParameterNames() { return MakeIterator.convert(config.getInitParameterNames()); } public ServletContext getServletContext() { return config.getServletContext(); } } 只有短短的几行代码，getInitParameterNames是这个类的核心，将Filter初始化参数名称有枚举类型转为Iterator。此类的主要作为是对filterConfig 封装。 重点来了，创建并初始化Dispatcher Java代码 public Dispatcher initDispatcher( HostConfig filterConfig ) { Dispatcher dispatcher = createDispatcher(filterConfig); dispatcher.init(); return dispatcher; } [java] view plaincopypublic Dispatcher initDispatcher( HostConfig filterConfig ) { Dispatcher dispatcher = createDispatcher(filterConfig); dispatcher.init(); return dispatcher; } 创—ispatcher，会读取 filterConfig 中的配置信息，将配置信息解析出来，封装成为一个Map，然后根绝servlet上下文和参数Map构造Dispatcher ：Java代码 private Dispatcher createDispatcher( HostConfig filterConfig ) { Map<string string> params = new HashMap<string string>(); for ( Iterator e = filterConfig.getInitParameterNames(); e.hasNext(); ) { String name = (String) e.next(); String value = filterConfig.getInitParameter(name); params.put(name, value); } return new Dispatcher(filterConfig.getServletContext(), params); } [java] view plaincopyprivate Dispatcher createDispatcher( HostConfig filterConfig ) { Map<string string> params = new HashMap<string string>(); for ( Iterator e = filterConfig.getInitParameterNames(); e.hasNext(); ) { String name = (String) e.next(); String value = filterConfig.getInitParameter(name); params.put(name, value); } return new Dispatcher(filterConfig.getServletContext(), params); } Dispatcher初始化，加载struts2的相关配置文件，将按照顺序逐一加载：default.properties，struts-default.xml,struts-plugin.xml,struts.xml，…… Java代码 /** *初始化过程中依次加载如下配置文件 */ public void init() { if (configurationManager == null ) { configurationManager = new ConfigurationManager(BeanSelectionProvider.DEFAULT_BEAN_NAME); } try { //加载org/apache/struts2/default.properties init_DefaultProperties(); // [1] //加载struts-default.xml,struts-plugin.xml,struts.xml init_TraditionalXmlConfigurations(); // [2] init_LegacyStrutsProperties(); // [3] //用户自己实现的ConfigurationProviders类 init_CustomConfigurationProviders(); // [5] //Filter的初始化参数 init_FilterInitParameters() ; // [6] init_AliasStandardObjects() ; // [7] Container container = init_PreloadConfiguration(); container.inject(this ); init_CheckConfigurationReloading(container); init_CheckWebLogicWorkaround(container); if (!dispatcherListeners.isEmpty()) { for (DispatcherListener l : dispatcherListeners) { l.dispatcherInitialized(this ); } } } catch (Exception ex) { if (LOG.isErrorEnabled()) LOG.error("Dispatcher initialization failed" , ex); throw new StrutsException(ex); } } [java] view plaincopy/** *初始化过程中依次加载如下配置文件 */ public void init() { if (configurationManager == null) { configurationManager = new ConfigurationManager(BeanSelectionProvider.DEFAULT_BEAN_NAME); } try { //加载org/apache/struts2/default.properties init_DefaultProperties(); // [1] //加载struts-default.xml,struts-plugin.xml,struts.xml init_TraditionalXmlConfigurations(); // [2] init_LegacyStrutsProperties(); // [3] //用户自己实现的ConfigurationProviders类 init_CustomConfigurationProviders(); // [5] //Filter的初始化参数 init_FilterInitParameters() ; // [6] init_AliasStandardObjects() ; // [7] Container container = init_PreloadConfiguration(); container.inject(this); init_CheckConfigurationReloading(container); init_CheckWebLogicWorkaround(container); if (!dispatcherListeners.isEmpty()) { for (DispatcherListener l : dispatcherListeners) { l.dispatcherInitialized(this); } } } catch (Exception ex) { if (LOG.isErrorEnabled()) LOG.error("Dispatcher initialization failed", ex); throw new StrutsException(ex); } } 初始化default.properties，具体的初始化操作在DefaultPropertiesProvider类中 Java代码 private void init_DefaultProperties() { configurationManager.addConfigurationProvider(new DefaultPropertiesProvider()); } [java] view plaincopyprivate void init_DefaultProperties() { configurationManager.addConfigurationProvider(new DefaultPropertiesProvider()); } 下面我们看下DefaultPropertiesProvider类源码： Java代码 public void register(ContainerBuilder builder, LocatableProperties props) throws ConfigurationException { Settings defaultSettings = null ; try { defaultSettings = new PropertiesSettings( "org/apache/struts2/default" ); } catch (Exception e) { throw new ConfigurationException( "Could not find or error in org/apache/struts2/default.properties" , e); } loadSettings(props, defaultSettings); } [java] view plaincopypublic void register(ContainerBuilder builder, LocatableProperties props) throws ConfigurationException { Settings defaultSettings = null; try { defaultSettings = new PropertiesSettings("org/apache/struts2/default"); } catch (Exception e) { throw new ConfigurationException("Could not find or error in org/apache/struts2/default.properties", e); } loadSettings(props, defaultSettings); } 其他的我们再次省略，大家可以浏览下各个初始化操作都加载了那些文件3、doFilter方法 doFilter是过滤器的执行方法，它拦截提交的HttpServletRequest请求，HttpServletResponse响应，作为strtus2的核心拦截器，在doFilter里面到底做了哪些工作，我们将逐行解读其源码，源码如下： Java代码 public void doFilter(ServletRequest req, ServletResponse res, FilterChain chain) throws IOException, ServletException { //父类向子类转：强转为http请求、响应 HttpServletRequest request = (HttpServletRequest) req; HttpServletResponse response = (HttpServletResponse) res; try { //设置编码和国际化 prepare.setEncodingAndLocale(request, response); //创建Action上下文（重点） prepare.createActionContext(request, response); prepare.assignDispatcherToThread(); if ( excludedPatterns != null && prepare.isUrlExcluded(request, excludedPatterns)) { chain.doFilter(request, response); } else { request = prepare.wrapRequest(request); ActionMapping mapping = prepare.findActionMapping(request, response, true ); if (mapping == null ) { boolean handled = execute.executeStaticResourceRequest(request, response); if (!handled) { chain.doFilter(request, response); } } else { execute.executeAction(request, response, mapping); } } } finally { prepare.cleanupRequest(request); } } [java] view plaincopy public void doFilter(ServletRequest req, ServletResponse res, FilterChain chain) throws IOException, ServletException { //父类向子类转：强转为http请求、响应 HttpServletRequest request = (HttpServletRequest) req; HttpServletResponse response = (HttpServletResponse) res; try { //设置编码和国际化 prepare.setEncodingAndLocale(request, response); //创建Action上下文（重点） prepare.createActionContext(request, response); prepare.assignDispatcherToThread(); if ( excludedPatterns != null && prepare.isUrlExcluded(request, excludedPatterns)) { chain.doFilter(request, response); } else { request = prepare.wrapRequest(request); ActionMapping mapping = prepare.findActionMapping(request, response, true); if (mapping == null) { boolean handled = execute.executeStaticResourceRequest(request, response); if (!handled) { chain.doFilter(request, response); } } else { execute.executeAction(request, response, mapping); } } } finally { prepare.cleanupRequest(request); } } setEncodingAndLocale调用了dispatcher方法的prepare方法： Java代码 /** * Sets the request encoding and locale on the response */ public void setEncodingAndLocale(HttpServletRequest request, HttpServletResponse response) { dispatcher.prepare(request, response); } [java] view plaincopy/** * Sets the request encoding and locale on the response */ public void setEncodingAndLocale(HttpServletRequest request, HttpServletResponse response) { dispatcher.prepare(request, response); } 下面我们看下prepare方法，这个方法很简单只是设置了encoding 、locale ，做的只是一些辅助的工作：Java代码 public void prepare(HttpServletRequest request, HttpServletResponse response) { String encoding = null ; if (defaultEncoding != null ) { encoding = defaultEncoding; } Locale locale = null ; if (defaultLocale != null ) { locale = LocalizedTextUtil.localeFromString(defaultLocale, request.getLocale()); } if (encoding != null ) { try { request.setCharacterEncoding(encoding); } catch (Exception e) { LOG.error("Error setting character encoding to '" + encoding + "' - ignoring." , e); } } if (locale != null ) { response.setLocale(locale); } if (paramsWorkaroundEnabled) { request.getParameter("foo" ); // simply read any parameter (existing or not) to "prime" the request } } [java] view plaincopypublic void prepare(HttpServletRequest request, HttpServletResponse response) { String encoding = null; if (defaultEncoding != null) { encoding = defaultEncoding; } Locale locale = null; if (defaultLocale != null) { locale = LocalizedTextUtil.localeFromString(defaultLocale, request.getLocale()); } if (encoding != null) { try { request.setCharacterEncoding(encoding); } catch (Exception e) { LOG.error("Error setting character encoding to '" + encoding + "' - ignoring.", e); } } if (locale != null) { response.setLocale(locale); } if (paramsWorkaroundEnabled) { request.getParameter("foo"); // simply read any parameter (existing or not) to "prime" the request } } Action上下文创建（重点） ActionContext是一个容器，这个容易主要存储request、session、application、parameters等相关信 息.ActionContext是一个线程的本地变量，这意味着不同的action之间不会共享ActionContext，所以也不用考虑线程安全问 题。其实质是一个Map，key是标示request、session、……的字符串，值是其对应的对象：Java代码 static ThreadLocal actionContext = new ThreadLocal(); Map<string object> context; [java] view plaincopystatic ThreadLocal actionContext = new ThreadLocal(); Map<string object> context; 下面我们看下如何创建action上下文的，代码如下： Java代码 /** *创建Action上下文，初始化thread local */ public ActionContext createActionContext(HttpServletRequest request, HttpServletResponse response) { ActionContext ctx; Integer counter = 1 ; Integer oldCounter = (Integer) request.getAttribute(CLEANUP_RECURSION_COUNTER); if (oldCounter != null ) { counter = oldCounter + 1 ; } //注意此处是从ThreadLocal中获取此ActionContext变量 ActionContext oldContext = ActionContext.getContext(); if (oldContext != null ) { // detected existing context, so we are probably in a forward ctx = new ActionContext( new HashMap<string object>(oldContext.getContextMap())); } else { ValueStack stack = dispatcher.getContainer().getInstance(ValueStackFactory.class ).createValueStack(); stack.getContext().putAll(dispatcher.createContextMap(request, response, null , servletContext)); //stack.getContext()返回的是一个Map<string>，根据此Map构造一个ActionContext ctx = new ActionContext(stack.getContext()); } request.setAttribute(CLEANUP_RECURSION_COUNTER, counter); //将ActionContext存如ThreadLocal ActionContext.setContext(ctx); return ctx; } [java] view plaincopy/** *创建Action上下文，初始化thread local */ public ActionContext createActionContext(HttpServletRequest request, HttpServletResponse response) { ActionContext ctx; Integer counter = 1; Integer oldCounter = (Integer) request.getAttribute(CLEANUP_RECURSION_COUNTER); if (oldCounter != null) { counter = oldCounter + 1; } //注意此处是从ThreadLocal中获取此ActionContext变量 ActionContext oldContext = ActionContext.getContext(); if (oldContext != null) { // detected existing context, so we are probably in a forward ctx = new ActionContext(new HashMap<string object>(oldContext.getContextMap())); } else { ValueStack stack = dispatcher.getContainer().getInstance(ValueStackFactory.class).createValueStack(); stack.getContext().putAll(dispatcher.createContextMap(request, response, null, servletContext)); //stack.getContext()返回的是一个Map<string>，根据此Map构造一个ActionContext ctx = new ActionContext(stack.getContext()); } request.setAttribute(CLEANUP_RECURSION_COUNTER, counter); //将ActionContext存如ThreadLocal ActionContext.setContext(ctx); return ctx; } 上面代码中dispatcher.createContextMap，如何封装相关参数： Java代码 public Map<string> createContextMap(HttpServletRequest request, HttpServletResponse response, ActionMapping mapping, ServletContext context) { // request map wrapping the http request objects Map requestMap = new RequestMap(request); // parameters map wrapping the http parameters. ActionMapping parameters are now handled and applied separately Map params = new HashMap(request.getParameterMap()); // session map wrapping the http session Map session = new SessionMap(request); // application map wrapping the ServletContext Map application = new ApplicationMap(context); //requestMap、params、session等Map封装成为一个上下文Map，逐个调用了map.put(Map p). Map<string> extraContext = createContextMap(requestMap, params, session, application, request, response, context); if (mapping != null ) { extraContext.put(ServletActionContext.ACTION_MAPPING, mapping); } return extraContext; } [java] view plaincopypublic Map<string> createContextMap(HttpServletRequest request, HttpServletResponse response, ActionMapping mapping, ServletContext context) { // request map wrapping the http request objects Map requestMap = new RequestMap(request); // parameters map wrapping the http parameters. ActionMapping parameters are now handled and applied separately Map params = new HashMap(request.getParameterMap()); // session map wrapping the http session Map session = new SessionMap(request); // application map wrapping the ServletContext Map application = new ApplicationMap(context); //requestMap、params、session等Map封装成为一个上下文Map，逐个调用了map.put(Map p). Map<string> extraContext = createContextMap(requestMap, params, session, application, request, response, context); if (mapping != null) { extraContext.put(ServletActionContext.ACTION_MAPPING, mapping); } return extraContext; } 我们简单看下RequestMap，其他的省略。RequestMap类实现了抽象Map，故其本身是一个Map，主要方法实现：Java代码 //map的get实现 public Object get(Object key) { return request.getAttribute(key.toString()); } //map的put实现 public Object put(Object key, Object value) { Object oldValue = get(key); entries = null ; request.setAttribute(key.toString(), value); return oldValue; } [java] view plaincopy//map的get实现 public Object get(Object key) { return request.getAttribute(key.toString()); } //map的put实现 public Object put(Object key, Object value) { Object oldValue = get(key); entries = null; request.setAttribute(key.toString(), value); return oldValue; } 下面是源码展示了如何执行Action控制器： Java代码 public void executeAction(HttpServletRequest request, HttpServletResponse response, ActionMapping mapping) throws ServletException { dispatcher.serviceAction(request, response, servletContext, mapping); } public void serviceAction(HttpServletRequest request, HttpServletResponse response, ServletContext context, ActionMapping mapping) throws ServletException { //封装执行的上下文环境，主要讲相关信息存储入map Map<string object> extraContext = createContextMap(request, response, mapping, context); // If there was a previous value stack, then create a new copy and pass it in to be used by the new Action ValueStack stack = (ValueStack) request.getAttribute(ServletActionContext.STRUTS_VALUESTACK_KEY); boolean nullStack = stack == null ; if (nullStack) { ActionContext ctx = ActionContext.getContext(); if (ctx != null ) { stack = ctx.getValueStack(); } } if (stack != null ) { extraContext.put(ActionContext.VALUE_STACK, valueStackFactory.createValueStack(stack)); } String timerKey = "Handling request from Dispatcher" ; try { UtilTimerStack.push(timerKey); //获取命名空间 String namespace = mapping.getNamespace(); //获取action配置的name属性 String name = mapping.getName(); //获取action配置的method属性 String method = mapping.getMethod(); Configuration config = configurationManager.getConfiguration(); //根据执行上下文参数，命名空间，名称等创建用户自定义Action的代理对象 ActionProxy proxy = config.getContainer().getInstance(ActionProxyFactory.class ).createActionProxy( namespace, name, method, extraContext, true , false ); request.setAttribute(ServletActionContext.STRUTS_VALUESTACK_KEY, proxy.getInvocation().getStack()); // if the ActionMapping says to go straight to a result, do it! //执行execute方法，并转向结果 if (mapping.getResult() != null ) { Result result = mapping.getResult(); result.execute(proxy.getInvocation()); } else { proxy.execute(); } // If there was a previous value stack then set it back onto the request if (!nullStack) { request.setAttribute(ServletActionContext.STRUTS_VALUESTACK_KEY, stack); } } catch (ConfigurationException e) { // WW-2874 Only log error if in devMode if (devMode) { String reqStr = request.getRequestURI(); if (request.getQueryString() != null ) { reqStr = reqStr + "?" + request.getQueryString(); } LOG.error("Could not find action or result/n" + reqStr, e); } else { LOG.warn("Could not find action or result" , e); } sendError(request, response, context, HttpServletResponse.SC_NOT_FOUND, e); } catch (Exception e) { sendError(request, response, context, HttpServletResponse.SC_INTERNAL_SERVER_ERROR, e); } finally { UtilTimerStack.pop(timerKey); } } [java] view plaincopypublic void executeAction(HttpServletRequest request, HttpServletResponse response, ActionMapping mapping) throws ServletException { dispatcher.serviceAction(request, response, servletContext, mapping); } public void serviceAction(HttpServletRequest request, HttpServletResponse response, ServletContext context, ActionMapping mapping) throws ServletException { //封装执行的上下文环境，主要讲相关信息存储入map Map<string object> extraContext = createContextMap(request, response, mapping, context); // If there was a previous value stack, then create a new copy and pass it in to be used by the new Action ValueStack stack = (ValueStack) request.getAttribute(ServletActionContext.STRUTS_VALUESTACK_KEY); boolean nullStack = stack == null; if (nullStack) { ActionContext ctx = ActionContext.getContext(); if (ctx != null) { stack = ctx.getValueStack(); } } if (stack != null) { extraContext.put(ActionContext.VALUE_STACK, valueStackFactory.createValueStack(stack)); } String timerKey = "Handling request from Dispatcher"; try { UtilTimerStack.push(timerKey); //获取命名空间 String namespace = mapping.getNamespace(); //获取action配置的name属性 String name = mapping.getName(); //获取action配置的method属性 String method = mapping.getMethod(); Configuration config = configurationManager.getConfiguration(); //根据执行上下文参数，命名空间，名称等创建用户自定义Action的代理对象 ActionProxy proxy = config.getContainer().getInstance(ActionProxyFactory.class).createActionProxy( namespace, name, method, extraContext, true, false); request.setAttribute(ServletActionContext.STRUTS_VALUESTACK_KEY, proxy.getInvocation().getStack()); // if the ActionMapping says to go straight to a result, do it! //执行execute方法，并转向结果 if (mapping.getResult() != null) { Result result = mapping.getResult(); result.execute(proxy.getInvocation()); } else { proxy.execute(); } // If there was a previous value stack then set it back onto the request if (!nullStack) { request.setAttribute(ServletActionContext.STRUTS_VALUESTACK_KEY, stack); } } catch (ConfigurationException e) { // WW-2874 Only log error if in devMode if(devMode) { String reqStr = request.getRequestURI(); if (request.getQueryString() != null) { reqStr = reqStr + "?" + request.getQueryString(); } LOG.error("Could not find action or result/n" + reqStr, e); } else { LOG.warn("Could not find action or result", e); } sendError(request, response, context, HttpServletResponse.SC_NOT_FOUND, e); } catch (Exception e) { sendError(request, response, context, HttpServletResponse.SC_INTERNAL_SERVER_ERROR, e); } finally { UtilTimerStack.pop(timerKey); } } 文中对如何解析Struts.xml，如何将URL与action映射匹配为分析，有需要的我后续补全，因为 StrutsXmlConfigurationProvider继承XmlConfigurationProvider，并在register方法回调父 类的register，有兴趣的可以深入阅读下下XmlConfigurationProvider源码： Java代码 public void register(ContainerBuilder containerBuilder, LocatableProperties props) throws ConfigurationException { if (servletContext != null && !containerBuilder.contains(ServletContext. class )) { containerBuilder.factory(ServletContext.class , new Factory<servletcontext>() { public ServletContext create(Context context) throws Exception { return servletContext; } }); } //调用父类的register，关键点所在 super .register(containerBuilder, props); } [java] view plaincopypublic void register(ContainerBuilder containerBuilder, LocatableProperties props) throws ConfigurationException { if (servletContext != null && !containerBuilder.contains(ServletContext.class)) { containerBuilder.factory(ServletContext.class, new Factory<servletcontext>() { public ServletContext create(Context context) throws Exception { return servletContext; } }); } //调用父类的register，关键点所在 super.register(containerBuilder, props); } struts2-core-2.2.1.jar包中struts-2.1.7.dtd对于Action的定义如下：Xml代码 [xml] view plaincopy 从上述DTD中可见Action元素可以含有name 、class 、method 、converter 属性。 XmlConfigurationProvider解析struts.xml配置的Action元素：Java代码 protected void addAction(Element actionElement, PackageConfig.Builder packageContext) throws ConfigurationException { String name = actionElement.getAttribute("name" ); String className = actionElement.getAttribute("class" ); String methodName = actionElement.getAttribute("method" ); Location location = DomHelper.getLocationObject(actionElement); if (location == null ) { LOG.warn("location null for " + className); } //methodName should be null if it's not set methodName = (methodName.trim().length() > 0 ) ? methodName.trim() : null ; // if there isnt a class name specified for an <action></action> then try to // use the default-class-ref from the <package></package> if (StringUtils.isEmpty(className)) { // if there is a package default-class-ref use that, otherwise use action support /* if (StringUtils.isNotEmpty(packageContext.getDefaultClassRef())) { className = packageContext.getDefaultClassRef(); } else { className = ActionSupport.class.getName(); }*/ } else { if (!verifyAction(className, name, location)) { if (LOG.isErrorEnabled()) LOG.error("Unable to verify action [#0] with class [#1], from [#2]" , name, className, location.toString()); return ; } } Map<string resultconfig> results; try { results = buildResults(actionElement, packageContext); } catch (ConfigurationException e) { throw new ConfigurationException( "Error building results for action " + name + " in namespace " + packageContext.getNamespace(), e, actionElement); } List<interceptormapping> interceptorList = buildInterceptorList(actionElement, packageContext); List<exceptionmappingconfig> exceptionMappings = buildExceptionMappings(actionElement, packageContext); ActionConfig actionConfig = new ActionConfig.Builder(packageContext.getName(), name, className) .methodName(methodName) .addResultConfigs(results) .addInterceptors(interceptorList) .addExceptionMappings(exceptionMappings) .addParams(XmlHelper.getParams(actionElement)) .location(location) .build(); packageContext.addActionConfig(name, actionConfig); if (LOG.isDebugEnabled()) { LOG.debug("Loaded " + (StringUtils.isNotEmpty(packageContext.getNamespace()) ? (packageContext.getNamespace() + "/" ) : "" ) + name + " in '" + packageContext.getName() + "' package:" + actionConfig); } } [java] view plaincopyprotected void addAction(Element actionElement, PackageConfig.Builder packageContext) throws ConfigurationException { String name = actionElement.getAttribute("name"); String className = actionElement.getAttribute("class"); String methodName = actionElement.getAttribute("method"); Location location = DomHelper.getLocationObject(actionElement); if (location == null) { LOG.warn("location null for " + className); } //methodName should be null if it's not set methodName = (methodName.trim().length() > 0) ? methodName.trim() : null; // if there isnt a class name specified for an <action></action> then try to // use the default-class-ref from the <package></package> if (StringUtils.isEmpty(className)) { // if there is a package default-class-ref use that, otherwise use action support /* if (StringUtils.isNotEmpty(packageContext.getDefaultClassRef())) { className = packageContext.getDefaultClassRef(); } else { className = ActionSupport.class.getName(); }*/ } else { if (!verifyAction(className, name, location)) { if (LOG.isErrorEnabled()) LOG.error("Unable to verify action [#0] with class [#1], from [#2]", name, className, location.toString()); return; } } Map<string resultconfig> results; try { results = buildResults(actionElement, packageContext); } catch (ConfigurationException e) { throw new ConfigurationException("Error building results for action " + name + " in namespace " + packageContext.getNamespace(), e, actionElement); } List<interceptormapping> interceptorList = buildInterceptorList(actionElement, packageContext); List<exceptionmappingconfig> exceptionMappings = buildExceptionMappings(actionElement, packageContext); ActionConfig actionConfig = new ActionConfig.Builder(packageContext.getName(), name, className) .methodName(methodName) .addResultConfigs(results) .addInterceptors(interceptorList) .addExceptionMappings(exceptionMappings) .addParams(XmlHelper.getParams(actionElement)) .location(location) .build(); packageContext.addActionConfig(name, actionConfig); if (LOG.isDebugEnabled()) { LOG.debug("Loaded " + (StringUtils.isNotEmpty(packageContext.getNamespace()) ? (packageContext.getNamespace() + "/") : "") + name + " in '" + packageContext.getName() + "' package:" + actionConfig); } } 工作中不涉及Struts2，本周工作有个2天的空档期，稍微看了下struts2的文档，写了个demo，从源码的角度研究了下运行原理，如有分析不当请指出，我后续逐步完善更正，大家共同提高。</exceptionmappingconfig></interceptormapping></string></exceptionmappingconfig></interceptormapping></string></servletcontext></servletcontext></string></string></string></string></string></string></string></string></string></string></string></string></string></string></string></string></string></string></pattern>