探究Struts2运行机制：StrutsPrepareAndExecuteFilter 源码剖析
作者：niumd
??blog：http://ari.iteye.com
?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。
- <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>
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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：
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- 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(); } }
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?? 首先看下FilterHostConfig ，源码如下：
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- 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。
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????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—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 ：
- 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，……
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- /***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); } }
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?? 初始化default.properties，具体的初始化操作在DefaultPropertiesProvider类中
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- private void init_DefaultProperties() { configurationManager.addConfigurationProvider(new DefaultPropertiesProvider()); }
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?? 下面我们看下DefaultPropertiesProvider类源码：
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- 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); }
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?? 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：
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- 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); } }
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????setEncodingAndLocale调用了dispatcher方法的prepare方法：
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- /** * Sets the request encoding and locale on the response */ public void setEncodingAndLocale(HttpServletRequest request, HttpServletResponse response) { dispatcher.prepare(request, response); }
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?? 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 } }
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?? 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;
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?? 下面我们看下如何创建action上下文的，代码如下：
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- /***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;}
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??? 上面代码中dispatcher.createContextMap，如何封装相关参数：
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- 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;}
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?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;}
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?? 下面是源码展示了如何执行Action控制器：
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