struts2运行机制

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：

<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：

 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 、executeprepare = 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：

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     

 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 ：

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，……

/***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.propertiesinit_DefaultProperties(); // [1]//加载struts-default.xml,struts-plugin.xml,struts.xmlinit_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

  

 private void init_DefaultProperties() {configurationManager.addConfigurationProvider(new DefaultPropertiesProvider());}

    

   下面我们看下DefaultPropertiesProvider类源码：

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);}

   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：

    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：

/*** 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：

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：

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：

/***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 forwardctx = 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ActionContextctx = new ActionContext(stack.getContext());}request.setAttribute(CLEANUP_RECURSION_COUNTER, counter);//将ActionContext存如ThreadLocalActionContext.setContext(ctx);return ctx;}

    上面代码中dispatcher.createContextMap，如何封装相关参数：

public Map<String,Object> createContextMap(HttpServletRequest request, HttpServletResponse response,ActionMapping mapping, ServletContext context) {// request map wrapping the http request objectsMap requestMap = new RequestMap(request);// parameters map wrapping the http parameters.  ActionMapping parameters are now handled and applied separatelyMap params = new HashMap(request.getParameterMap());// session map wrapping the http sessionMap session = new SessionMap(request);// application map wrapping the ServletContextMap 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：

//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：

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mapMap<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 ActionValueStack 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 requestif (!nullStack) {request.setAttribute(ServletActionContext.STRUTS_VALUESTACK_KEY, stack);}} catch (ConfigurationException e) {// WW-2874 Only log error if in devModeif(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：

 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：

<!ELEMENT action (param|result|interceptor-ref|exception-mapping)*><!ATTLIST actionname CDATA #REQUIREDclass CDATA #IMPLIEDmethod CDATA #IMPLIEDconverter 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：

   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 setmethodName = (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);}}