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。

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>

<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：

 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：

  

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     

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 ：

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，……

 

/**
*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

  

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：

  

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：

   

 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：

   

/**
     * 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：

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：

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：

   

/**
*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：

 

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：

//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：

 

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,