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  • 探究Struts2运行机制，知识积累

    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
    1. <filter>  
    2.     <filter-name>struts2</filter-name>  
    3.     <filter-class>org.apache.struts2.dispatcher.ng.filter.StrutsPrepareAndExecuteFilter</filter-class>  
    4. </filter>  
    5. <filter-mapping>  
    6.     <filter-name>struts2</filter-name>  
    7.     <url-pattern>/*</url-pattern>  
    8. </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  收藏代码
    1.  public void init(FilterConfig filterConfig) throws ServletException {  
    2.         InitOperations init = new InitOperations();  
    3.         try {  
    4. //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  
    5.             FilterHostConfig config = new FilterHostConfig(filterConfig);  
    6. // 初始化struts内部日志  
    7.            init.initLogging(config);  
    8. //<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>  
    9.             Dispatcher dispatcher = init.initDispatcher(config);  
    10.             init.initStaticContentLoader(config, dispatcher);  
    11. //初始化类属性：prepare 、execute   
    12.             prepare = new PrepareOperations(filterConfig.getServletContext(), dispatcher);  
    13.             execute = new ExecuteOperations(filterConfig.getServletContext(), dispatcher);  
    14.             this.excludedPatterns = init.buildExcludedPatternsList(dispatcher);  
    15. //回调空的postInit方法  
    16.             postInit(dispatcher, filterConfig);  
    17.         } finally {  
    18.             init.cleanup();  
    19.         }  
    20.  }  
     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  收藏代码
    1. public class FilterHostConfig implements HostConfig {  
    2.   
    3.     private FilterConfig config;  
    4.     /** 
    5.      *构造函数   
    6.      */      
    7.     public FilterHostConfig(FilterConfig config) {  
    8.         this.config = config;  
    9.     }  
    10.     /** 
    11.      *  根据init-param配置的param-name获取param-value的值 
    12.      */    
    13.     public String getInitParameter(String key) {  
    14.         return config.getInitParameter(key);  
    15.     }  
    16.        /** 
    17.          *  返回初始化参数名的List 
    18.      */   
    19.     public Iterator<String> getInitParameterNames() {  
    20.         return MakeIterator.convert(config.getInitParameterNames());  
    21.     }  
    22.   
    23.     public ServletContext getServletContext() {  
    24.         return config.getServletContext();  
    25.     }  
    26. }  
    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
    1. public Dispatcher initDispatcher( HostConfig filterConfig ) {  
    2.        Dispatcher dispatcher = createDispatcher(filterConfig);  
    3.        dispatcher.init();  
    4.        return dispatcher;  
    5.    }  
     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
    1. private Dispatcher createDispatcher( HostConfig filterConfig ) {  
    2.         Map<String, String> params = new HashMap<String, String>();  
    3.         for ( Iterator e = filterConfig.getInitParameterNames(); e.hasNext(); ) {  
    4.             String name = (String) e.next();  
    5.             String value = filterConfig.getInitParameter(name);  
    6.             params.put(name, value);  
    7.         }  
    8.         return new Dispatcher(filterConfig.getServletContext(), params);  
    9.     }  
    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
    1. /** 
    2. *初始化过程中依次加载如下配置文件 
    3. */  
    4. public void init() {  
    5.   
    6.         if (configurationManager == null) {  
    7.             configurationManager = new ConfigurationManager(BeanSelectionProvider.DEFAULT_BEAN_NAME);  
    8.         }  
    9.   
    10.         try {  
    11.             //加载org/apache/struts2/default.properties  
    12.             init_DefaultProperties(); // [1]  
    13.            //加载struts-default.xml,struts-plugin.xml,struts.xml  
    14.             init_TraditionalXmlConfigurations(); // [2]  
    15.             init_LegacyStrutsProperties(); // [3]  
    16.            //用户自己实现的ConfigurationProviders类              
    17.         init_CustomConfigurationProviders(); // [5]  
    18.             //Filter的初始化参数  
    19.         init_FilterInitParameters() ; // [6]  
    20.             init_AliasStandardObjects() ; // [7]  
    21.   
    22.             Container container = init_PreloadConfiguration();  
    23.             container.inject(this);  
    24.             init_CheckConfigurationReloading(container);  
    25.             init_CheckWebLogicWorkaround(container);  
    26.   
    27.             if (!dispatcherListeners.isEmpty()) {  
    28.                 for (DispatcherListener l : dispatcherListeners) {  
    29.                     l.dispatcherInitialized(this);  
    30.                 }  
    31.             }  
    32.         } catch (Exception ex) {  
    33.             if (LOG.isErrorEnabled())  
    34.                 LOG.error("Dispatcher initialization failed", ex);  
    35.             throw new StrutsException(ex);  
    36.         }  
    37.     }  
    /**
*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
    1. private void init_DefaultProperties() {  
    2.        configurationManager.addConfigurationProvider(new DefaultPropertiesProvider());  
    3.    }  
     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
    1. public void register(ContainerBuilder builder, LocatableProperties props)  
    2.             throws ConfigurationException {  
    3.           
    4.         Settings defaultSettings = null;  
    5.         try {  
    6.             defaultSettings = new PropertiesSettings("org/apache/struts2/default");  
    7.         } catch (Exception e) {  
    8.             throw new ConfigurationException("Could not find or error in org/apache/struts2/default.properties", e);  
    9.         }  
    10.           
    11.         loadSettings(props, defaultSettings);  
    12.     }  
    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
    1.  public void doFilter(ServletRequest req, ServletResponse res, FilterChain chain) throws IOException, ServletException {  
    2.      //父类向子类转：强转为http请求、响应  
    3.      HttpServletRequest request = (HttpServletRequest) req;  
    4.      HttpServletResponse response = (HttpServletResponse) res;  
    5.   
    6.      try {  
    7.          //设置编码和国际化  
    8.          prepare.setEncodingAndLocale(request, response);  
    9.           //创建Action上下文（重点）  
    10.          prepare.createActionContext(request, response);  
    11.          prepare.assignDispatcherToThread();  
    12. if ( excludedPatterns != null && prepare.isUrlExcluded(request, excludedPatterns)) {  
    13.     chain.doFilter(request, response);  
    14. } else {  
    15.     request = prepare.wrapRequest(request);  
    16.     ActionMapping mapping = prepare.findActionMapping(request, response, true);  
    17.     if (mapping == null) {  
    18.         boolean handled = execute.executeStaticResourceRequest(request, response);  
    19.         if (!handled) {  
    20.             chain.doFilter(request, response);  
    21.         }  
    22.     } else {  
    23.         execute.executeAction(request, response, mapping);  
    24.     }  
    25. }  
    26.      } finally {  
    27.          prepare.cleanupRequest(request);  
    28.      }  
    29.  }  
        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
    1. /** 
    2.      * Sets the request encoding and locale on the response 
    3.      */  
    4.     public void setEncodingAndLocale(HttpServletRequest request, HttpServletResponse response) {  
    5.         dispatcher.prepare(request, response);  
    6.     }  
    /**
     * 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
    1. public void prepare(HttpServletRequest request, HttpServletResponse response) {  
    2.         String encoding = null;  
    3.         if (defaultEncoding != null) {  
    4.             encoding = defaultEncoding;  
    5.         }  
    6.   
    7.         Locale locale = null;  
    8.         if (defaultLocale != null) {  
    9.             locale = LocalizedTextUtil.localeFromString(defaultLocale, request.getLocale());  
    10.         }  
    11.   
    12.         if (encoding != null) {  
    13.             try {  
    14.                 request.setCharacterEncoding(encoding);  
    15.             } catch (Exception e) {  
    16.                 LOG.error("Error setting character encoding to '" + encoding + "' - ignoring.", e);  
    17.             }  
    18.         }  
    19.   
    20.         if (locale != null) {  
    21.             response.setLocale(locale);  
    22.         }  
    23.   
    24.         if (paramsWorkaroundEnabled) {  
    25.             request.getParameter("foo"); // simply read any parameter (existing or not) to "prime" the request  
    26.         }  
    27.     }  
    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
    1. static ThreadLocal actionContext = new ThreadLocal();  
    2. 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  收藏代码
    1. /** 
    2. *创建Action上下文，初始化thread local 
    3. */  
    4. public ActionContext createActionContext(HttpServletRequest request, HttpServletResponse response) {  
    5.     ActionContext ctx;  
    6.     Integer counter = 1;  
    7.     Integer oldCounter = (Integer) request.getAttribute(CLEANUP_RECURSION_COUNTER);  
    8.     if (oldCounter != null) {  
    9.         counter = oldCounter + 1;  
    10.     }  
    11.     //注意此处是从ThreadLocal中获取此ActionContext变量  
    12.     ActionContext oldContext = ActionContext.getContext();  
    13.     if (oldContext != null) {  
    14.         // detected existing context, so we are probably in a forward  
    15.         ctx = new ActionContext(new HashMap<String, Object>(oldContext.getContextMap()));  
    16.     } else {  
    17.         ValueStack stack = dispatcher.getContainer().getInstance(ValueStackFactory.class).createValueStack();  
    18.         stack.getContext().putAll(dispatcher.createContextMap(request, response, null, servletContext));  
    19.         //stack.getContext()返回的是一个Map<String，Object>，根据此Map构造一个ActionContext  
    20.         ctx = new ActionContext(stack.getContext());  
    21.     }  
    22.     request.setAttribute(CLEANUP_RECURSION_COUNTER, counter);  
    23.     //将ActionContext存如ThreadLocal  
    24.     ActionContext.setContext(ctx);  
    25.     return ctx;  
    26. }  
    /**
*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
    1. public Map<String,Object> createContextMap(HttpServletRequest request, HttpServletResponse response,  
    2.             ActionMapping mapping, ServletContext context) {  
    3.   
    4.         // request map wrapping the http request objects  
    5.         Map requestMap = new RequestMap(request);  
    6.   
    7.         // parameters map wrapping the http parameters.  ActionMapping parameters are now handled and applied separately  
    8.         Map params = new HashMap(request.getParameterMap());  
    9.   
    10.         // session map wrapping the http session  
    11.         Map session = new SessionMap(request);  
    12.   
    13.         // application map wrapping the ServletContext  
    14.         Map application = new ApplicationMap(context);  
    15.                 //requestMap、params、session等Map封装成为一个上下文Map，逐个调用了map.put(Map p).  
    16.         Map<String,Object> extraContext = createContextMap(requestMap, params, session, application, request, response, context);  
    17.   
    18.         if (mapping != null) {  
    19.             extraContext.put(ServletActionContext.ACTION_MAPPING, mapping);  
    20.         }  
    21.         return extraContext;  
    22. }  
    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
    1. //map的get实现  
    2. public Object get(Object key) {  
    3.     return request.getAttribute(key.toString());  
    4. }  
    5. //map的put实现  
    6. public Object put(Object key, Object value) {  
    7.     Object oldValue = get(key);  
    8.     entries = null;  
    9.     request.setAttribute(key.toString(), value);  
    10.     return oldValue;  
    11. }  
    //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
    1. public void executeAction(HttpServletRequest request, HttpServletResponse response, ActionMapping mapping) throws ServletException {  
    2.     dispatcher.serviceAction(request, response, servletContext, mapping);  
    3. }  
    4.   
    5.     public void serviceAction(HttpServletRequest request, HttpServletResponse response, ServletContext context,  
    6.                               ActionMapping mapping) throws ServletException {  
    7.                 //封装执行的上下文环境，主要讲相关信息存储入map  
    8.         Map<String, Object> extraContext = createContextMap(request, response, mapping, context);  
    9.   
    10.         // If there was a previous value stack, then create a new copy and pass it in to be used by the new Action  
    11.         ValueStack stack = (ValueStack) request.getAttribute(ServletActionContext.STRUTS_VALUESTACK_KEY);  
    12.         boolean nullStack = stack == null;  
    13.         if (nullStack) {  
    14.             ActionContext ctx = ActionContext.getContext();  
    15.             if (ctx != null) {  
    16.                 stack = ctx.getValueStack();  
    17.             }  
    18.         }  
    19.         if (stack != null) {  
    20.             extraContext.put(ActionContext.VALUE_STACK, valueStackFactory.createValueStack(stack));  
    21.         }  
    22.   
    23.         String timerKey = "Handling request from Dispatcher";  
    24.         try {  
    25.             UtilTimerStack.push(timerKey);  
    26.             //获取命名空间  
    27.             String namespace = mapping.getNamespace();  
    28.             //获取action配置的name属性  
    29.             String name = mapping.getName();  
    30.             //获取action配置的method属性  
    31.             String method = mapping.getMethod();  
    32.   
    33.             Configuration config = configurationManager.getConfiguration();  
    34.             //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  
    35.             ActionProxy proxy = config.getContainer().getInstance(ActionProxyFactory.class).createActionProxy(  
    36.                     namespace, name, method, extraContext, true, false);  
    37.   
    38.             request.setAttribute(ServletActionContext.STRUTS_VALUESTACK_KEY, proxy.getInvocation().getStack());  
    39.   
    40.             // if the ActionMapping says to go straight to a result, do it!  
    41.                     //执行execute方法，并转向结果  
    42.             if (mapping.getResult() != null) {  
    43.                 Result result = mapping.getResult();  
    44.                 result.execute(proxy.getInvocation());  
    45.             } else {  
    46.                 proxy.execute();  
    47.             }  
    48.   
    49.             // If there was a previous value stack then set it back onto the request  
    50.             if (!nullStack) {  
    51.                 request.setAttribute(ServletActionContext.STRUTS_VALUESTACK_KEY, stack);  
    52.             }  
    53.         } catch (ConfigurationException e) {  
    54.             // WW-2874 Only log error if in devMode  
    55.             if(devMode) {  
    56.                 String reqStr = request.getRequestURI();  
    57.                 if (request.getQueryString() != null) {  
    58.                     reqStr = reqStr + "?" + request.getQueryString();  
    59.                 }  
    60.                 LOG.error("Could not find action or result " + reqStr, e);  
    61.             }  
    62.             else {  
    63.                 LOG.warn("Could not find action or result", e);  
    64.             }  
    65.             sendError(request, response, context, HttpServletResponse.SC_NOT_FOUND, e);  
    66.         } catch (Exception e) {  
    67.             sendError(request, response, context, HttpServletResponse.SC_INTERNAL_SERVER_ERROR, e);  
    68.         } finally {  
    69.             UtilTimerStack.pop(timerKey);  
    70.         }  
    71.     }  
    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
" + 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
    1. public void register(ContainerBuilder containerBuilder, LocatableProperties props) throws ConfigurationException {  
    2.        if (servletContext != null && !containerBuilder.contains(ServletContext.class)) {  
    3.            containerBuilder.factory(ServletContext.class, new Factory<ServletContext>() {  
    4.                public ServletContext create(Context context) throws Exception {  
    5.                    return servletContext;  
    6.                }  
    7.            });  
    8.        }  
    9.        //调用父类的register，关键点所在  
    10.        super.register(containerBuilder, props);  
    11.    }  
     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
    1. <!ELEMENT action (param|result|interceptor-ref|exception-mapping)*>  
    2. <!ATTLIST action  
    3.     name CDATA #REQUIRED  
    4.     class CDATA #IMPLIED  
    5.     method CDATA #IMPLIED  
    6.     converter CDATA #IMPLIED  
    7. >  
    <!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
    1. protected void addAction(Element actionElement, PackageConfig.Builder packageContext) throws ConfigurationException {  
    2.      String name = actionElement.getAttribute("name");  
    3.      String className = actionElement.getAttribute("class");  
    4.      String methodName = actionElement.getAttribute("method");  
    5.      Location location = DomHelper.getLocationObject(actionElement);  
    6.   
    7.      if (location == null) {  
    8.          LOG.warn("location null for " + className);  
    9.      }  
    10.      //methodName should be null if it's not set  
    11.      methodName = (methodName.trim().length() > 0) ? methodName.trim() : null;  
    12.   
    13.      // if there isnt a class name specified for an <action/> then try to  
    14.      // use the default-class-ref from the <package/>  
    15.      if (StringUtils.isEmpty(className)) {  
    16.          // if there is a package default-class-ref use that, otherwise use action support  
    17.         /* if (StringUtils.isNotEmpty(packageContext.getDefaultClassRef())) { 
    18.              className = packageContext.getDefaultClassRef(); 
    19.          } else { 
    20.              className = ActionSupport.class.getName(); 
    21.          }*/  
    22.   
    23.      } else {  
    24.          if (!verifyAction(className, name, location)) {  
    25.              if (LOG.isErrorEnabled())  
    26.                  LOG.error("Unable to verify action [#0] with class [#1], from [#2]", name, className, location.toString());  
    27.              return;  
    28.          }  
    29.      }  
    30.   
    31.   
    32.   
    33.      Map<String, ResultConfig> results;  
    34.      try {  
    35.          results = buildResults(actionElement, packageContext);  
    36.      } catch (ConfigurationException e) {  
    37.          throw new ConfigurationException("Error building results for action " + name + " in namespace " + packageContext.getNamespace(), e, actionElement);  
    38.      }  
    39.   
    40.      List<InterceptorMapping> interceptorList = buildInterceptorList(actionElement, packageContext);  
    41.   
    42.      List<ExceptionMappingConfig> exceptionMappings = buildExceptionMappings(actionElement, packageContext);  
    43.   
    44.      ActionConfig actionConfig = new ActionConfig.Builder(packageContext.getName(), name, className)  
    45.              .methodName(methodName)  
    46.              .addResultConfigs(results)  
    47.              .addInterceptors(interceptorList)  
    48.              .addExceptionMappings(exceptionMappings)  
    49.              .addParams(XmlHelper.getParams(actionElement))  
    50.              .location(location)  
    51.              .build();  
    52.      packageContext.addActionConfig(name, actionConfig);  
    53.   
    54.      if (LOG.isDebugEnabled()) {  
    55.          LOG.debug("Loaded " + (StringUtils.isNotEmpty(packageContext.getNamespace()) ? (packageContext.getNamespace() + "/") : "") + name + " in '" + packageContext.getName() + "' package:" + actionConfig);  
    56.      }  
    57.  }  
       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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  • 原文地址：https://www.cnblogs.com/summer3/p/6541124.html
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