struts2 分析

转自：http://www.javaeye.com/topic/450979

 

1. Struts2架构图

        请求首先通过Filter chain，Filter主要包括ActionContextCleanUp，它主要清理当前线程的ActionContext和Dispatcher；FilterDispatcher主要通过AcionMapper来决定需要调用哪个Action。
        ActionMapper取得了ActionMapping后，在Dispatcher的serviceAction方法里创建ActionProxy，ActionProxy创建ActionInvocation，然后ActionInvocation调用Interceptors，执行Action本身，创建Result并返回，当然，如果要在返回之前做些什么，可以实现PreResultListener。

2. Struts2部分类介绍
这部分从Struts2参考文档中翻译就可以了。
ActionMapper
        ActionMapper其实是HttpServletRequest和Action调用请求的一个映射，它屏蔽了Action对于Request等java Servlet类的依赖。Struts2中它的默认实现类是DefaultActionMapper，ActionMapper很大的用处可以根据自己的需要来设计url格式，它自己也有Restful的实现，具体可以参考文档的docs/actionmapper.html。
ActionProxy&ActionInvocation
        Action的一个代理，由ActionProxyFactory创建，它本身不包括Action实例，默认实现DefaultActionProxy是由ActionInvocation持有Action实例。ActionProxy作用是如何取得Action，无论是本地还是远程。而ActionInvocation的作用是如何执行Action，拦截器的功能就是在ActionInvocation中实现的。
ConfigurationProvider&Configuration
        ConfigurationProvider就是Struts2中配置文件的解析器，Struts2中的配置文件主要是尤其实现类XmlConfigurationProvider及其子类StrutsXmlConfigurationProvider来解析。

3. Struts2请求流程
1、客户端发送请求
2、请求先通过ActionContextCleanUp-->FilterDispatcher
3、FilterDispatcher通过ActionMapper来决定这个Request需要调用哪个Action
4、如果ActionMapper决定调用某个Action，FilterDispatcher把请求的处理交给ActionProxy，这儿已经转到它的Delegate--Dispatcher来执行
5、ActionProxy根据ActionMapping和ConfigurationManager找到需要调用的Action类
6、ActionProxy创建一个ActionInvocation的实例
7、ActionInvocation调用真正的Action，当然这涉及到相关拦截器的调用
8、Action执行完毕，ActionInvocation创建Result并返回，当然，如果要在返回之前做些什么，可以实现PreResultListener。添加PreResultListener可以在Interceptor中实现，不知道其它还有什么方式？

4. Struts2(2.1.2)部分源码阅读
    从org.apache.struts2.dispatcher.FilterDispatcher开始

//创建Dispatcher，此类是一个Delegate，它是真正完成根据url解析，读取对应Action的地方
public void init(FilterConfig filterConfig) throws ServletException {
    try {
        this.filterConfig = filterConfig;

        initLogging();

        dispatcher = createDispatcher(filterConfig);
        dispatcher.init();
        dispatcher.getContainer().inject(this);
        //读取初始参数pakages，调用parse()，解析成类似/org/apache/struts2/static,/template的数组
        String param = filterConfig.getInitParameter("packages");
        String packages = "org.apache.struts2.static template org.apache.struts2.interceptor.debugging";
        if (param != null) {
            packages = param + " " + packages;
        }
        this.pathPrefixes = parse(packages);
    } finally {
        ActionContext.setContext(null);
    }
}

    //创建Dispatcher，此类是一个Delegate，它是真正完成根据url解析，读取对应Action的地方
    public void init(FilterConfig filterConfig) throws ServletException {
        try {
            this.filterConfig = filterConfig;

            initLogging();

            dispatcher = createDispatcher(filterConfig);
            dispatcher.init();
            dispatcher.getContainer().inject(this);
            //读取初始参数pakages，调用parse()，解析成类似/org/apache/struts2/static,/template的数组
            String param = filterConfig.getInitParameter("packages");
            String packages = "org.apache.struts2.static template org.apache.struts2.interceptor.debugging";
            if (param != null) {
                packages = param + " " + packages;
            }
            this.pathPrefixes = parse(packages);
        } finally {
            ActionContext.setContext(null);
        }
    }

     顺着流程我们看Disptcher的init方法。init方法里就是初始读取一些配置文件等，先看init_DefaultProperties，主要是读取properties配置文件。

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

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

    打开DefaultPropertiesProvider

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);
 }

 //PropertiesSettings
 //读取org/apache/struts2/default.properties的配置信息，如果项目中需要覆盖，可以在classpath里的struts.properties里覆写
 public PropertiesSettings(String name) {

     URL settingsUrl = ClassLoaderUtils.getResource(name + ".properties", getClass());

     if (settingsUrl == null) {
         LOG.debug(name + ".properties missing");
         settings = new LocatableProperties();
         return;
     }

     settings = new LocatableProperties(new LocationImpl(null, settingsUrl.toString()));

     // Load settings
     InputStream in = null;
     try {
         in = settingsUrl.openStream();
         settings.load(in);
     } catch (IOException e) {
         throw new StrutsException("Could not load " + name + ".properties:" + e, e);
     } finally {
         if(in != null) {
             try {
                 in.close();
             } catch(IOException io) {
                 LOG.warn("Unable to close input stream", io);
             }
         }
     }
 }

   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);
    }

    //PropertiesSettings
    //读取org/apache/struts2/default.properties的配置信息，如果项目中需要覆盖，可以在classpath里的struts.properties里覆写
    public PropertiesSettings(String name) {
        
        URL settingsUrl = ClassLoaderUtils.getResource(name + ".properties", getClass());
        
        if (settingsUrl == null) {
            LOG.debug(name + ".properties missing");
            settings = new LocatableProperties();
            return;
        }
        
        settings = new LocatableProperties(new LocationImpl(null, settingsUrl.toString()));

        // Load settings
        InputStream in = null;
        try {
            in = settingsUrl.openStream();
            settings.load(in);
        } catch (IOException e) {
            throw new StrutsException("Could not load " + name + ".properties:" + e, e);
        } finally {
            if(in != null) {
                try {
                    in.close();
                } catch(IOException io) {
                    LOG.warn("Unable to close input stream", io);
                }
            }
        }
    }

    再来看init_TraditionalXmlConfigurations方法，这个是读取struts-default.xml和Struts.xml的方法。

private void init_TraditionalXmlConfigurations() {
    //首先读取web.xml中的config初始参数值
    //如果没有配置就使用默认的"struts-default.xml,struts-plugin.xml,struts.xml"，
    //这儿就可以看出为什么默认的配置文件必须取名为这三个名称了
    //如果不想使用默认的名称，直接在web.xml中配置config初始参数即可
    String configPaths = initParams.get("config");
    if (configPaths == null) {
        configPaths = DEFAULT_CONFIGURATION_PATHS;
    }
    String[] files = configPaths.split("//s*[,]//s*");
    //依次解析配置文件，xwork.xml单独解析
    for (String file : files) {
        if (file.endsWith(".xml")) {
            if ("xwork.xml".equals(file)) {
                configurationManager.addConfigurationProvider(new XmlConfigurationProvider(file, false));
            } else {
                configurationManager.addConfigurationProvider(new StrutsXmlConfigurationProvider(file, false, servletContext));
            }
        } else {
            throw new IllegalArgumentException("Invalid configuration file name");
        }
    }
}

    private void init_TraditionalXmlConfigurations() {
        //首先读取web.xml中的config初始参数值
        //如果没有配置就使用默认的"struts-default.xml,struts-plugin.xml,struts.xml"，
        //这儿就可以看出为什么默认的配置文件必须取名为这三个名称了
        //如果不想使用默认的名称，直接在web.xml中配置config初始参数即可
        String configPaths = initParams.get("config");
        if (configPaths == null) {
            configPaths = DEFAULT_CONFIGURATION_PATHS;
        }
        String[] files = configPaths.split("//s*[,]//s*");
        //依次解析配置文件，xwork.xml单独解析
        for (String file : files) {
            if (file.endsWith(".xml")) {
                if ("xwork.xml".equals(file)) {
                    configurationManager.addConfigurationProvider(new XmlConfigurationProvider(file, false));
                } else {
                    configurationManager.addConfigurationProvider(new StrutsXmlConfigurationProvider(file, false, servletContext));
                }
            } else {
                throw new IllegalArgumentException("Invalid configuration file name");
            }
        }
    }

    对于其它配置文件只用StrutsXmlConfigurationProvider，此类继承XmlConfigurationProvider，而XmlConfigurationProvider又实现ConfigurationProvider接口。类XmlConfigurationProvider负责配置文件的读取和解析，addAction()方法负责读取<action>标签，并将数据保存在ActionConfig中；addResultTypes()方法负责将<result-type>标签转化为ResultTypeConfig对象；loadInterceptors()方法负责将<interceptor>标签转化为InterceptorConfi对象；loadInterceptorStack()方法负责将<interceptor-ref>标签转化为InterceptorStackConfig对象；loadInterceptorStacks()方法负责将<interceptor-stack>标签转化成InterceptorStackConfig对象。而上面的方法最终会被addPackage()方法调用，将所读取到的数据汇集到PackageConfig对象中。来看XmlConfigurationProvider的源代码，详细的我自己也就大体浏览了一下，各位可以自己研读。

protected PackageConfig addPackage(Element packageElement) throws ConfigurationException {
    PackageConfig.Builder newPackage = buildPackageContext(packageElement);

    if (newPackage.isNeedsRefresh()) {
        return newPackage.build();
    }
    .

    addResultTypes(newPackage, packageElement);
    loadInterceptors(newPackage, packageElement);
    loadDefaultInterceptorRef(newPackage, packageElement);
    loadDefaultClassRef(newPackage, packageElement);
    loadGlobalResults(newPackage, packageElement);
    loadGobalExceptionMappings(newPackage, packageElement);
    NodeList actionList = packageElement.getElementsByTagName("action");

    for (int i = 0; i < actionList.getLength(); i++) {
        Element actionElement = (Element) actionList.item(i);
        addAction(actionElement, newPackage);
    }
    loadDefaultActionRef(newPackage, packageElement);
    PackageConfig cfg = newPackage.build();
    configuration.addPackageConfig(cfg.getName(), cfg);
    return cfg;
}

    protected PackageConfig addPackage(Element packageElement) throws ConfigurationException {
        PackageConfig.Builder newPackage = buildPackageContext(packageElement);

        if (newPackage.isNeedsRefresh()) {
            return newPackage.build();
        }
        .

        addResultTypes(newPackage, packageElement);
        loadInterceptors(newPackage, packageElement);
        loadDefaultInterceptorRef(newPackage, packageElement);
        loadDefaultClassRef(newPackage, packageElement);
        loadGlobalResults(newPackage, packageElement);
        loadGobalExceptionMappings(newPackage, packageElement);
        NodeList actionList = packageElement.getElementsByTagName("action");

        for (int i = 0; i < actionList.getLength(); i++) {
            Element actionElement = (Element) actionList.item(i);
            addAction(actionElement, newPackage);
        }
        loadDefaultActionRef(newPackage, packageElement);
        PackageConfig cfg = newPackage.build();
        configuration.addPackageConfig(cfg.getName(), cfg);
        return cfg;
    }

    这儿发现一个配置上的小技巧，我的xwork2.0.*是没有的，但是看源码是看到xwork2.1.*是可以的。继续看XmlConfigurationProvider的源代码：

Java代码

private List loadConfigurationFiles(String fileName, Element includeElement) {
    List<Document> docs = new ArrayList<Document>();
    if (!includedFileNames.contains(fileName)) {

            Element rootElement = doc.getDocumentElement();
            NodeList children = rootElement.getChildNodes();
            int childSize = children.getLength();

            for (int i = 0; i < childSize; i++) {
                Node childNode = children.item(i);

                if (childNode instanceof Element) {
                    Element child = (Element) childNode;

                    final String nodeName = child.getNodeName();
                    //解析每个action配置是，对于include文件可以使用通配符*来进行配置
                    //如Struts.xml中可配置成<include file="actions_*.xml"/>
                    if (nodeName.equals("include")) {
                        String includeFileName = child.getAttribute("file");
                        if(includeFileName.indexOf('*') != -1 ) {
                            ClassPathFinder wildcardFinder = new ClassPathFinder();
                            wildcardFinder.setPattern(includeFileName);
                            Vector<String> wildcardMatches = wildcardFinder.findMatches();
                            for (String match : wildcardMatches) {
                                docs.addAll(loadConfigurationFiles(match, child));
                            }
                        }
                        else {

                            docs.addAll(loadConfigurationFiles(includeFileName, child));
                        }
                }
            }
            }
            docs.add(doc);
            loadedFileUrls.add(url.toString());
        }
    }
    return docs;
}

init_CustomConfigurationProviders方式初始自定义的Provider，配置类全名和实现ConfigurationProvider接口，用逗号隔开即可。

private void init_CustomConfigurationProviders() {
    String configProvs = initParams.get("configProviders");
    if (configProvs != null) {
        String[] classes = configProvs.split("//s*[,]//s*");
        for (String cname : classes) {
            try {
                Class cls = ClassLoaderUtils.loadClass(cname, this.getClass());
                ConfigurationProvider prov = (ConfigurationProvider)cls.newInstance();
                configurationManager.addConfigurationProvider(prov);
            }

        }
    }
}

    private void init_CustomConfigurationProviders() {
        String configProvs = initParams.get("configProviders");
        if (configProvs != null) {
            String[] classes = configProvs.split("//s*[,]//s*");
            for (String cname : classes) {
                try {
                    Class cls = ClassLoaderUtils.loadClass(cname, this.getClass());
                    ConfigurationProvider prov = (ConfigurationProvider)cls.newInstance();
                    configurationManager.addConfigurationProvider(prov);
                }
                
            }
        }
    }

   好了，现在再回到FilterDispatcher，每次发送一个Request，FilterDispatcher都会调用doFilter方法。

public void doFilter(ServletRequest req, ServletResponse res, FilterChain chain) throws IOException, ServletException {

    HttpServletRequest request = (HttpServletRequest) req;
    HttpServletResponse response = (HttpServletResponse) res;
    ServletContext servletContext = getServletContext();

    String timerKey = "FilterDispatcher_doFilter: ";
    try {
        ValueStack stack = dispatcher.getContainer().getInstance(ValueStackFactory.class).createValueStack();
        ActionContext ctx = new ActionContext(stack.getContext());
        ActionContext.setContext(ctx);

        UtilTimerStack.push(timerKey);
        //根据content type来使用不同的Request封装，可以参见Dispatcher的wrapRequest
        request = prepareDispatcherAndWrapRequest(request, response);
        ActionMapping mapping;
        try {
            //根据url取得对应的Action的配置信息--ActionMapping，actionMapper是通过Container的inject注入的
            mapping = actionMapper.getMapping(request, dispatcher.getConfigurationManager());
        } catch (Exception ex) {
            log.error("error getting ActionMapping", ex);
            dispatcher.sendError(request, response, servletContext, HttpServletResponse.SC_INTERNAL_SERVER_ERROR, ex);
            return;
        }
        //如果找不到对应的action配置，则直接返回。比如你输入***.jsp等等
        //这儿有个例外，就是如果path是以“/struts”开头，则到初始参数packages配置的包路径去查找对应的静态资源并输出到页面流中，当然.class文件除外。如果再没有则跳转到404
        if (mapping == null) {
            // there is no action in this request, should we look for a static resource?
            String resourcePath = RequestUtils.getServletPath(request);

            if ("".equals(resourcePath) && null != request.getPathInfo()) {
                resourcePath = request.getPathInfo();
            }

            if (serveStatic && resourcePath.startsWith("/struts")) {
                String name = resourcePath.substring("/struts".length());
                findStaticResource(name, request, response);
            } else {
                chain.doFilter(request, response);
            }
            return;
        }
        //正式开始Action的方法了
        dispatcher.serviceAction(request, response, servletContext, mapping);

    } finally {
        try {
            ActionContextCleanUp.cleanUp(req);
        } finally {
            UtilTimerStack.pop(timerKey);
        }
    }
}

    public void doFilter(ServletRequest req, ServletResponse res, FilterChain chain) throws IOException, ServletException {

        HttpServletRequest request = (HttpServletRequest) req;
        HttpServletResponse response = (HttpServletResponse) res;
        ServletContext servletContext = getServletContext();

        String timerKey = "FilterDispatcher_doFilter: ";
        try {
            ValueStack stack = dispatcher.getContainer().getInstance(ValueStackFactory.class).createValueStack();
            ActionContext ctx = new ActionContext(stack.getContext());
            ActionContext.setContext(ctx);
            
            UtilTimerStack.push(timerKey);
            //根据content type来使用不同的Request封装，可以参见Dispatcher的wrapRequest
            request = prepareDispatcherAndWrapRequest(request, response);
            ActionMapping mapping;
            try {
                //根据url取得对应的Action的配置信息--ActionMapping，actionMapper是通过Container的inject注入的
                mapping = actionMapper.getMapping(request, dispatcher.getConfigurationManager());
            } catch (Exception ex) {
                log.error("error getting ActionMapping", ex);
                dispatcher.sendError(request, response, servletContext, HttpServletResponse.SC_INTERNAL_SERVER_ERROR, ex);
                return;
            }
            //如果找不到对应的action配置，则直接返回。比如你输入***.jsp等等
            //这儿有个例外，就是如果path是以“/struts”开头，则到初始参数packages配置的包路径去查找对应的静态资源并输出到页面流中，当然.class文件除外。如果再没有则跳转到404
            if (mapping == null) {
                // there is no action in this request, should we look for a static resource?
                String resourcePath = RequestUtils.getServletPath(request);

                if ("".equals(resourcePath) && null != request.getPathInfo()) {
                    resourcePath = request.getPathInfo();
                }

                if (serveStatic && resourcePath.startsWith("/struts")) {
                    String name = resourcePath.substring("/struts".length());
                    findStaticResource(name, request, response);
                } else {
                    chain.doFilter(request, response);
                }
                return;
            }
            //正式开始Action的方法了
            dispatcher.serviceAction(request, response, servletContext, mapping);

        } finally {
            try {
                ActionContextCleanUp.cleanUp(req);
            } finally {
                UtilTimerStack.pop(timerKey);
            }
        }
    }

    Dispatcher类的serviceAction方法：

public void serviceAction(HttpServletRequest request, HttpServletResponse response, ServletContext context,ActionMapping mapping) throws ServletException {

    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);
    if (stack != null) {
        extraContext.put(ActionContext.VALUE_STACK, valueStackFactory.createValueStack(stack));
    }

    String timerKey = "Handling request from Dispatcher";
    try {
        UtilTimerStack.push(timerKey);
        String namespace = mapping.getNamespace();
        String name = mapping.getName();
        String method = mapping.getMethod();

        Configuration config = configurationManager.getConfiguration();
        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!
        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 (stack != null) {
            request.setAttribute(ServletActionContext.STRUTS_VALUESTACK_KEY, stack);
        }
    } catch (ConfigurationException e) {
        LOG.error("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);
    }
}

    public void serviceAction(HttpServletRequest request, HttpServletResponse response, ServletContext context,ActionMapping mapping) throws ServletException {

        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);
        if (stack != null) {
            extraContext.put(ActionContext.VALUE_STACK, valueStackFactory.createValueStack(stack));
        }

        String timerKey = "Handling request from Dispatcher";
        try {
            UtilTimerStack.push(timerKey);
            String namespace = mapping.getNamespace();
            String name = mapping.getName();
            String method = mapping.getMethod();

            Configuration config = configurationManager.getConfiguration();
            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!
            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 (stack != null) {
                request.setAttribute(ServletActionContext.STRUTS_VALUESTACK_KEY, stack);
            }
        } catch (ConfigurationException e) {
            LOG.error("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);
        }
    }

    第一句createContextMap()方法，该方法主要把Application、Session、Request的key value值拷贝到Map中，并放在HashMap<String,Object>中，可以参见createContextMap方法：

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);
    Map<String,Object> extraContext = createContextMap(requestMap, params, session, application, request, response, context);
    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);
        Map<String,Object> extraContext = createContextMap(requestMap, params, session, application, request, response, context);
        extraContext.put(ServletActionContext.ACTION_MAPPING, mapping);
        return extraContext;
    }

    后面才是最主要的--ActionProxy，ActionInvocation。ActionProxy是Action的一个代理类，也就是说Action的调用是通过ActionProxy实现的，其实就是调用了ActionProxy.execute()方法，而该方法又调用了ActionInvocation.invoke()方法。归根到底，最后调用的是DefaultActionInvocation.invokeAction()方法。先看DefaultActionInvocation的init方法。

public void init(ActionProxy proxy) {
    this.proxy = proxy;
    Map contextMap = createContextMap();

    // Setting this so that other classes, like object factories, can use the ActionProxy and other
    // contextual information to operate
    ActionContext actionContext = ActionContext.getContext();

    if(actionContext != null) {
        actionContext.setActionInvocation(this);
    }
    //创建Action，可Struts2里是每次请求都新建一个Action
    createAction(contextMap);

    if (pushAction) {
        stack.push(action);
        contextMap.put("action", action);
    }

    invocationContext = new ActionContext(contextMap);
    invocationContext.setName(proxy.getActionName());

    // get a new List so we don't get problems with the iterator if someone changes the list
    List interceptorList = new ArrayList(proxy.getConfig().getInterceptors());
    interceptors = interceptorList.iterator();
}

protected void createAction(Map contextMap) {
    // load action
    String timerKey = "actionCreate: "+proxy.getActionName();
    try {
        UtilTimerStack.push(timerKey);
        //这儿默认建立Action是StrutsObjectFactory，实际中我使用的时候都是使用Spring创建的Action，这个时候使用的是SpringObjectFactory
        action = objectFactory.buildAction(proxy.getActionName(), proxy.getNamespace(), proxy.getConfig(), contextMap);
    }
    ..
    } finally {
        UtilTimerStack.pop(timerKey);
    }

    if (actionEventListener != null) {
        action = actionEventListener.prepare(action, stack);
    }
}

    public void init(ActionProxy proxy) {
        this.proxy = proxy;
        Map contextMap = createContextMap();

        // Setting this so that other classes, like object factories, can use the ActionProxy and other
        // contextual information to operate
        ActionContext actionContext = ActionContext.getContext();

        if(actionContext != null) {
            actionContext.setActionInvocation(this);
        }
        //创建Action，可Struts2里是每次请求都新建一个Action
        createAction(contextMap);

        if (pushAction) {
            stack.push(action);
            contextMap.put("action", action);
        }

        invocationContext = new ActionContext(contextMap);
        invocationContext.setName(proxy.getActionName());

        // get a new List so we don't get problems with the iterator if someone changes the list
        List interceptorList = new ArrayList(proxy.getConfig().getInterceptors());
        interceptors = interceptorList.iterator();
    }

    protected void createAction(Map contextMap) {
        // load action
        String timerKey = "actionCreate: "+proxy.getActionName();
        try {
            UtilTimerStack.push(timerKey);
            //这儿默认建立Action是StrutsObjectFactory，实际中我使用的时候都是使用Spring创建的Action，这个时候使用的是SpringObjectFactory
            action = objectFactory.buildAction(proxy.getActionName(), proxy.getNamespace(), proxy.getConfig(), contextMap);
        } 
        ..
        } finally {
            UtilTimerStack.pop(timerKey);
        }

        if (actionEventListener != null) {
            action = actionEventListener.prepare(action, stack);
        }
    }

    接下来看看DefaultActionInvocation 的invoke方法。

Java代码

 public void init(ActionProxy proxy) {
     this.proxy = proxy;
     Map contextMap = createContextMap();

     // Setting this so that other classes, like object factories, can use the ActionProxy and other
     // contextual information to operate
     ActionContext actionContext = ActionContext.getContext();

     if(actionContext != null) {
         actionContext.setActionInvocation(this);
     }
     //创建Action，可Struts2里是每次请求都新建一个Action
     createAction(contextMap);

     if (pushAction) {
         stack.push(action);
         contextMap.put("action", action);
     }

     invocationContext = new ActionContext(contextMap);
     invocationContext.setName(proxy.getActionName());

     // get a new List so we don't get problems with the iterator if someone changes the list
     List interceptorList = new ArrayList(proxy.getConfig().getInterceptors());
     interceptors = interceptorList.iterator();
 }

 protected void createAction(Map contextMap) {
     // load action
     String timerKey = "actionCreate: "+proxy.getActionName();
     try {
         UtilTimerStack.push(timerKey);
         //这儿默认建立Action是StrutsObjectFactory，实际中我使用的时候都是使用Spring创建的Action，这个时候使用的是SpringObjectFactory
         action = objectFactory.buildAction(proxy.getActionName(), proxy.getNamespace(), proxy.getConfig(), contextMap);
     }
     ..
     } finally {
         UtilTimerStack.pop(timerKey);
     }

     if (actionEventListener != null) {
         action = actionEventListener.prepare(action, stack);
     }
 }

 //接下来看看DefaultActionInvocation 的invoke方法。
public String invoke() throws Exception {
     String profileKey = "invoke: ";
     try {
         UtilTimerStack.push(profileKey);

         if (executed) {
             throw new IllegalStateException("Action has already executed");
         }
             //先执行interceptors
         if (interceptors.hasNext()) {
             final InterceptorMapping interceptor = (InterceptorMapping) interceptors.next();
             UtilTimerStack.profile("interceptor: "+interceptor.getName(),
                     new UtilTimerStack.ProfilingBlock<String>() {
                         public String doProfiling() throws Exception {
                             resultCode = interceptor.getInterceptor().intercept(DefaultActionInvocation.this);
                             return null;
                         }
             });
         } else {
                     //interceptor执行完了之后执行action
             resultCode = invokeActionOnly();
         }

         // this is needed because the result will be executed, then control will return to the Interceptor, which will
         // return above and flow through again
         if (!executed) {
                     //在Result返回之前调用preResultListeners
             if (preResultListeners != null) {
                 for (Iterator iterator = preResultListeners.iterator();
                     iterator.hasNext();) {
                     PreResultListener listener = (PreResultListener) iterator.next();

                     String _profileKey="preResultListener: ";
                     try {
                         UtilTimerStack.push(_profileKey);
                         listener.beforeResult(this, resultCode);
                     }
                     finally {
                         UtilTimerStack.pop(_profileKey);
                     }
                 }
             }

             // now execute the result, if we're supposed to
             if (proxy.getExecuteResult()) {
                 executeResult();
             }

             executed = true;
         }

         return resultCode;
     }
     finally {
         UtilTimerStack.pop(profileKey);
     }
 }

看程序中的if(interceptors.hasNext())语句，当然，interceptors里存储的是interceptorMapping列表（它包括一个Interceptor和一个name），所有的截拦器必须实现Interceptor的intercept方法，而该方法的参数恰恰又是ActionInvocation，在intercept方法中还是调用invocation.invoke()，从而实现了一个Interceptor链的调用。当所有的Interceptor执行完，最后调用invokeActionOnly方法来执行Action相应的方法。

protected String invokeAction(Object action, ActionConfig actionConfig) throws Exception {
    String methodName = proxy.getMethod();
    String timerKey = "invokeAction: "+proxy.getActionName();
    try {
        UtilTimerStack.push(timerKey);

        boolean methodCalled = false;
        Object methodResult = null;
        Method method = null;
        try {
            //获得需要执行的方法
            method = getAction().getClass().getMethod(methodName, new Class[0]);
        } catch (NoSuchMethodException e) {
            //如果没有对应的方法，则使用do+Xxxx来再次获得方法
            try {
                String altMethodName = "do" + methodName.substring(0, 1).toUpperCase() + methodName.substring(1);
                method = getAction().getClass().getMethod(altMethodName, new Class[0]);
            } catch (NoSuchMethodException e1) {
                // well, give the unknown handler a shot
                if (unknownHandler != null) {
                    try {
                        methodResult = unknownHandler.handleUnknownActionMethod(action, methodName);
                        methodCalled = true;
                    } catch (NoSuchMethodException e2) {
                        // throw the original one
                        throw e;
                    }
                } else {
                    throw e;
                }
            }
        }

        if (!methodCalled) {
            methodResult = method.invoke(action, new Object[0]);
        }
        //根据不同的Result类型返回不同值
        //如输出流Result
        if (methodResult instanceof Result) {
            this.explicitResult = (Result) methodResult;
            return null;
        } else {
            return (String) methodResult;
        }
    } catch (NoSuchMethodException e) {
        throw new IllegalArgumentException("The " + methodName + "() is not defined in action " + getAction().getClass() + "");
    } catch (InvocationTargetException e) {
        // We try to return the source exception.
        Throwable t = e.getTargetException();

        if (actionEventListener != null) {
            String result = actionEventListener.handleException(t, getStack());
            if (result != null) {
                return result;
            }
        }
        if (t instanceof Exception) {
            throw(Exception) t;
        } else {
            throw e;
        }
    } finally {
        UtilTimerStack.pop(timerKey);
    }
}

    protected String invokeAction(Object action, ActionConfig actionConfig) throws Exception {
        String methodName = proxy.getMethod();
        String timerKey = "invokeAction: "+proxy.getActionName();
        try {
            UtilTimerStack.push(timerKey);
            
            boolean methodCalled = false;
            Object methodResult = null;
            Method method = null;
            try {
                //获得需要执行的方法
                method = getAction().getClass().getMethod(methodName, new Class[0]);
            } catch (NoSuchMethodException e) {
                //如果没有对应的方法，则使用do+Xxxx来再次获得方法
                try {
                    String altMethodName = "do" + methodName.substring(0, 1).toUpperCase() + methodName.substring(1);
                    method = getAction().getClass().getMethod(altMethodName, new Class[0]);
                } catch (NoSuchMethodException e1) {
                    // well, give the unknown handler a shot
                    if (unknownHandler != null) {
                        try {
                            methodResult = unknownHandler.handleUnknownActionMethod(action, methodName);
                            methodCalled = true;
                        } catch (NoSuchMethodException e2) {
                            // throw the original one
                            throw e;
                        }
                    } else {
                        throw e;
                    }
                }
            }
            
            if (!methodCalled) {
                methodResult = method.invoke(action, new Object[0]);
            }
            //根据不同的Result类型返回不同值
            //如输出流Result
            if (methodResult instanceof Result) {
                this.explicitResult = (Result) methodResult;
                return null;
            } else {
                return (String) methodResult;
            }
        } catch (NoSuchMethodException e) {
            throw new IllegalArgumentException("The " + methodName + "() is not defined in action " + getAction().getClass() + "");
        } catch (InvocationTargetException e) {
            // We try to return the source exception.
            Throwable t = e.getTargetException();

            if (actionEventListener != null) {
                String result = actionEventListener.handleException(t, getStack());
                if (result != null) {
                    return result;
                }
            }
            if (t instanceof Exception) {
                throw(Exception) t;
            } else {
                throw e;
            }
        } finally {
            UtilTimerStack.pop(timerKey);
        }
    }

    好了，action执行完了，还要根据ResultConfig返回到view，也就是在invoke方法中调用executeResult方法。

private void executeResult() throws Exception {
     //根据ResultConfig创建Result
     result = createResult();
     String timerKey = "executeResult: "+getResultCode();
     try {
         UtilTimerStack.push(timerKey);
         if (result != null) {
             //这儿正式执行:)
             //可以参考Result的实现，如用了比较多的ServletDispatcherResult,ServletActionRedirectResult,ServletRedirectResult
             result.execute(this);
         } else if (resultCode != null && !Action.NONE.equals(resultCode)) {
             throw new ConfigurationException("No result defined for action " + getAction().getClass().getName()
                     + " and result " + getResultCode(), proxy.getConfig());
         } else {
             if (LOG.isDebugEnabled()) {
                 LOG.debug("No result returned for action "+getAction().getClass().getName()+" at "+proxy.getConfig().getLocation());
             }
         }
     } finally {
         UtilTimerStack.pop(timerKey);
     }
 }
 public Result createResult() throws Exception {
     if (explicitResult != null) {
         Result ret = explicitResult;
         explicitResult = null;;
         return ret;
     }
     ActionConfig config = proxy.getConfig();
     Map results = config.getResults();
     ResultConfig resultConfig = null;
     synchronized (config) {
         try {
             //根据result名称获得ResultConfig，resultCode就是result的name
             resultConfig = (ResultConfig) results.get(resultCode);
         } catch (NullPointerException e) {
         }
         if (resultConfig == null) {
             //如果找不到对应name的ResultConfig，则使用name为*的Result
             resultConfig = (ResultConfig) results.get("*");
         }
     }
     if (resultConfig != null) {
         try {
             //参照StrutsObjectFactory的代码
             Result result = objectFactory.buildResult(resultConfig, invocationContext.getContextMap());
             return result;
         } catch (Exception e) {
             LOG.error("There was an exception while instantiating the result of type " + resultConfig.getClassName(), e);
             throw new XWorkException(e, resultConfig);
         }
     } else if (resultCode != null && !Action.NONE.equals(resultCode) && unknownHandler != null) {
         return unknownHandler.handleUnknownResult(invocationContext, proxy.getActionName(), proxy.getConfig(), resultCode);
     }
     return null;
 }
 //StrutsObjectFactory
 public Result buildResult(ResultConfig resultConfig, Map extraContext) throws Exception {
     String resultClassName = resultConfig.getClassName();
     if (resultClassName == null)
         return null;
     //创建Result，因为Result是有状态的，所以每次请求都新建一个
     Object result = buildBean(resultClassName, extraContext);
     //这句很重要，后面将会谈到，reflectionProvider参见OgnlReflectionProvider；
     //resultConfig.getParams()就是result配置文件里所配置的参数<param></param>
     //setProperties方法最终调用的是Ognl类的setValue方法
     //这句其实就是把param名值设置到根对象result上
     reflectionProvider.setProperties(resultConfig.getParams(), result, extraContext);
     if (result instanceof Result)
         return (Result) result;
     throw new ConfigurationException(result.getClass().getName() + " does not implement Result.");
 }

   private void executeResult() throws Exception {
        //根据ResultConfig创建Result
        result = createResult();
        String timerKey = "executeResult: "+getResultCode();
        try {
            UtilTimerStack.push(timerKey);
            if (result != null) {
                //这儿正式执行:)
                //可以参考Result的实现，如用了比较多的ServletDispatcherResult,ServletActionRedirectResult,ServletRedirectResult
                result.execute(this);
            } else if (resultCode != null && !Action.NONE.equals(resultCode)) {
                throw new ConfigurationException("No result defined for action " + getAction().getClass().getName() 
                        + " and result " + getResultCode(), proxy.getConfig());
            } else {
                if (LOG.isDebugEnabled()) {
                    LOG.debug("No result returned for action "+getAction().getClass().getName()+" at "+proxy.getConfig().getLocation());
                }
            }
        } finally {
            UtilTimerStack.pop(timerKey);
        }
    }
    public Result createResult() throws Exception {
        if (explicitResult != null) {
            Result ret = explicitResult;
            explicitResult = null;;
            return ret;
        }
        ActionConfig config = proxy.getConfig();
        Map results = config.getResults();
        ResultConfig resultConfig = null;
        synchronized (config) {
            try {
                //根据result名称获得ResultConfig，resultCode就是result的name
                resultConfig = (ResultConfig) results.get(resultCode);
            } catch (NullPointerException e) {
            }
            if (resultConfig == null) {
                //如果找不到对应name的ResultConfig，则使用name为*的Result
                resultConfig = (ResultConfig) results.get("*");
            }
        }
        if (resultConfig != null) {
            try {
                //参照StrutsObjectFactory的代码
                Result result = objectFactory.buildResult(resultConfig, invocationContext.getContextMap());
                return result;
            } catch (Exception e) {
                LOG.error("There was an exception while instantiating the result of type " + resultConfig.getClassName(), e);
                throw new XWorkException(e, resultConfig);
            }
        } else if (resultCode != null && !Action.NONE.equals(resultCode) && unknownHandler != null) {
            return unknownHandler.handleUnknownResult(invocationContext, proxy.getActionName(), proxy.getConfig(), resultCode);
        }
        return null;
    }
    //StrutsObjectFactory
    public Result buildResult(ResultConfig resultConfig, Map extraContext) throws Exception {
        String resultClassName = resultConfig.getClassName();
        if (resultClassName == null)
            return null;
        //创建Result，因为Result是有状态的，所以每次请求都新建一个
        Object result = buildBean(resultClassName, extraContext);
        //这句很重要，后面将会谈到，reflectionProvider参见OgnlReflectionProvider；
        //resultConfig.getParams()就是result配置文件里所配置的参数<param></param>
        //setProperties方法最终调用的是Ognl类的setValue方法
        //这句其实就是把param名值设置到根对象result上
        reflectionProvider.setProperties(resultConfig.getParams(), result, extraContext);
        if (result instanceof Result)
            return (Result) result;
        throw new ConfigurationException(result.getClass().getName() + " does not implement Result.");
    }

   这样，一个Struts2的请求流程基本上就结束了。