探究Struts2运行机制：StrutsPrepareAndExecuteFilter 源码剖析

原文地址：http://ari.iteye.com/blog/829843



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。
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  收藏代码
<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> 
   
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  收藏代码
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(); 
        } 
} 

   首先看下FilterHostConfig ，源码如下：
 
Java代码  收藏代码
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(); 
    } 
} 
   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  收藏代码
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  收藏代码
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); 
    } 
  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  收藏代码
/**
*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default.properties，具体的初始化操作在DefaultPropertiesProvider类中
 
Java代码  收藏代码
private void init_DefaultProperties() { 
       configurationManager.addConfigurationProvider(new DefaultPropertiesProvider()); 
   } 
   
   下面我们看下DefaultPropertiesProvider类源码：
 
Java代码  收藏代码
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); 
    } 

   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  收藏代码
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); 
     } 
} 

    setEncodingAndLocale调用了dispatcher方法的prepare方法：
  
Java代码  收藏代码
/**
     * 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  收藏代码
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 
        } 
    } 
  
   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  收藏代码
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  收藏代码
/**
*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; 
} 

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

Java代码  收藏代码
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; 
} 

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  收藏代码
//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; 
} 

   下面是源码展示了如何执行Action控制器：

Java代码  收藏代码
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); 
        } 
    } 

   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  收藏代码
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); 
   } 
  

     struts2-core-2.2.1.jar包中struts-2.1.7.dtd对于Action的定义如下：
Xml代码  收藏代码
<!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  收藏代码
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); 
     } 
} 

  
     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。