探究Struts2运行机制：StrutsPrepareAndExecuteFilter 源码剖析

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   <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>   <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  ExecuteOperations execute             protected  PrepareOperations prepare            

 

    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 void destroy()            继承自Filter，用于资源释放  void doFilter(ServletRequest req, ServletResponse res, FilterChain chain)            继承自Filter，执行方法  void init(FilterConfig filterConfig)            继承自Filter，初始化参数 protected  void postInit(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();           }    }   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); //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 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();       }   }   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(); } }

   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;      }   public Dispatcher initDispatcher( HostConfig filterConfig ) { Dispatcher dispatcher = createDispatcher(filterConfig); dispatcher.init(); return dispatcher; }

     创建Dispatcher，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);       }   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); }

  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);           }       }   /** *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());      }   private 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);       }   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); }

 

   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);        }    }   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);       }   /** * 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           }       }   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 } }

   

   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;   static 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，Object>，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;   }   /** *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，Object>，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,Object> 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,Object> extraContext = createContextMap(requestMap, params, session, application, request, response, context);             if (mapping != null) {               extraContext.put(ServletActionContext.ACTION_MAPPING, mapping);           }           return extraContext;   }   public Map<String,Object> 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,Object> 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;   }   //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);           }       }   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); } }

 

   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);      }   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); }

   

 

     struts2-core-2.2.1.jar包中struts-2.1.7.dtd对于Action的定义如下：

Xml代码   <!ELEMENT action (param|result|interceptor-ref|exception-mapping)*>  <!ATTLIST action       name CDATA #REQUIRED       class CDATA #IMPLIED       method CDATA #IMPLIED       converter CDATA #IMPLIED   >   <!ELEMENT action (param|result|interceptor-ref|exception-mapping)*> <!ATTLIST action name CDATA #REQUIRED class CDATA #IMPLIED method CDATA #IMPLIED converter CDATA #IMPLIED >

    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/> then try to        // use the default-class-ref from the <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);        }    }   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/> then try to // use the default-class-ref from the <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。

       

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