Struts2源码阅读--请求流程

[img][/img]Struts包介绍

（http://www.blogjava.net/lzhidj/archive/2008/07/10/213898.html）（大部分叙述性的文字和图从其文中拷贝）： 包名
说明

org.apache.struts2. components
该包封装视图组件，Struts2在视图组件上有了很大加强，不仅增加了组件的属性个数，更新增了几个非常有用的组件，如updownselect、doubleselect、datetimepicker、token、tree等。

另外，Struts2可视化视图组件开始支持主题(theme)，缺省情况下，使用自带的缺省主题，如果要自定义页面效果，需要将组件的theme属性设置为simple。

org.apache.struts2. config
该包定义与配置相关的接口和类。实际上，工程中的xml和properties文件的读取和解析都是由WebWork完成的，Struts只做了少量的工作。

org.apache.struts2.dispatcher
Struts2的核心包，最重要的类都放在该包中。

org.apache.struts2.impl
该包只定义了3个类，他们是StrutsActionProxy、StrutsActionProxyFactory、StrutsObjectFactory，这三个类都是对xwork的扩展。

org.apache.struts2.interceptor
定义内置的截拦器。

org.apache.struts2.util
实用包。

org.apache.struts2.validators
只定义了一个类：DWRValidator。

org.apache.struts2.views
提供freemarker、jsp、velocity等不同类型的页面呈现。


下表是对一些重要类的说明：

类名
说明

org.apache.struts2.dispatcher. Dispatcher
该类有两个作用：

1、初始化

2、调用指定的Action的execute()方法。

org.apache.struts2.dispatcher. FilterDispatcher
     这是一个过滤器。文档中已明确说明，如果没有经验，配置时请将url-pattern的值设成/*。

    该类有四个作用：

    1、执行Action

    2、清理ActionContext，避免内存泄漏

    3、处理静态内容（Serving static content）

    4、为请求启动xwork’s的截拦器链。

com.opensymphony.xwork2. ActionProxy
Action的代理接口。

com.opensymphony.xwork2. ctionProxyFactory
  生产ActionProxy的工厂。

com.opensymphony.xwork2.ActionInvocation
负责调用Action和截拦器。

com.opensymphony.xwork2.config.providers. XmlConfigurationProvider
负责Struts2的配置文件的解析。



Struts体系结构

Struts工作机制
    1、客户端初始化一个指向Servlet容器（例如Tomcat）的请求；
    2、这个请求经过一系列的过滤器（Filter）（这些过滤器中有一个叫做ActionContextCleanUp的可选过滤器，这个过滤器对于Struts2和其他框架的集成很有帮助，例如：SiteMesh Plugin）；
    3、接着FilterDispatcher被调用，FilterDispatcher询问ActionMapper来决定这个请求是否需要调用某个Action；
    4、如果ActionMapper决定需要调用某个Action，FilterDispatcher把请求的处理交给ActionProxy；
    5、ActionProxy通过Configuration Manager询问框架的配置文件，找到需要调用的Action类；
    6、ActionProxy创建一个ActionInvocation的实例。
    7、ActionInvocation实例使用命名模式来调用，在调用Action的过程前后，涉及到相关拦截器（Intercepter）的调用。
    8、一旦Action执行完毕，ActionInvocation负责根据struts.xml中的配置找到对应的返回结果。返回结果通常是（但不总是，也可能是另外的一个Action链）一个需要被表示的JSP或者FreeMarker的模版。在表示的过程中可以使用Struts2 框架中继承的标签。在这个过程中需要涉及到ActionMapper。
Struts源码分析
    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 {
         this.filterConfig = filterConfig;
         
        dispatcher = createDispatcher(filterConfig);
        dispatcher.init();
        //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);
    }
    顾名思义，init方法里就是初始读取一些属性配置文件，先看init_DefaultProperties。
    public void init() {

        if (configurationManager == null) {
            configurationManager = new ConfigurationManager(BeanSelectionProvider.DEFAULT_BEAN_NAME);
        }

        init_DefaultProperties(); // [1]
        init_TraditionalXmlConfigurations(); // [2]
        init_LegacyStrutsProperties(); // [3]
        init_ZeroConfiguration(); // [4]
        init_CustomConfigurationProviders(); // [5]
        init_MethodConfigurationProvider();
        init_FilterInitParameters() ; // [6]
        init_AliasStandardObjects() ; // [7]

        Container container = init_PreloadConfiguration();
        init_CheckConfigurationReloading(container);
        init_CheckWebLogicWorkaround(container);

    }
    private void init_DefaultProperties() {
        configurationManager.addConfigurationProvider(new DefaultPropertiesProvider());
    }
    //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的类型为LocatableProperties，继承Properties
        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Action配置的方法。
    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");
            }
        }
    }
    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。
    protected PackageConfig addPackage(Element packageElement) throws ConfigurationException {
        PackageConfig.Builder newPackage = buildPackageContext(packageElement);

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

        if (LOG.isDebugEnabled()) {
            LOG.debug("Loaded " + newPackage);
        }

        // add result types (and default result) to this package
        addResultTypes(newPackage, packageElement);

        // load the interceptors and interceptor stacks for this package
        loadInterceptors(newPackage, packageElement);

        // load the default interceptor reference for this package
        loadDefaultInterceptorRef(newPackage, packageElement);

        // load the default class ref for this package
        loadDefaultClassRef(newPackage, packageElement);

        // load the global result list for this package
        loadGlobalResults(newPackage, packageElement);

        // load the global exception handler list for this package
        loadGobalExceptionMappings(newPackage, packageElement);

        // get actions
        NodeList actionList = packageElement.getElementsByTagName("action");

        for (int i = 0; i < actionList.getLength(); i++) {
            Element actionElement = (Element) actionList.item(i);
            addAction(actionElement, newPackage);
        }

        // load the default action reference for this package
        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东西，我的xwork2.0.*是没有的，但是看源码是看到xwork2.1.*是可以的。看如下代码：
    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 ) {
                                // handleWildCardIncludes(includeFileName, docs, child);
                                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接口就可以。
    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 {
            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 {
                    // this is a normal request, let it pass through
                    chain.doFilter(request, response);
                }
                // The framework did its job here
                return;
            }
            //正式开始执行Action的方法了
            dispatcher.serviceAction(request, response, servletContext, mapping);

        } finally {
            try {
                ActionContextCleanUp.cleanUp(req);
            } finally {
                UtilTimerStack.pop(timerKey);
            }
        }
    }
    来看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.getFactory().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, extraContext, true, false);
            proxy.setMethod(method);
            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) {
            throw new ServletException(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 HashMap<String,Object> createContextMap(Map requestMap,
                                    Map parameterMap,
                                    Map sessionMap,
                                    Map applicationMap,
                                    HttpServletRequest request,
                                    HttpServletResponse response,
                                    ServletContext servletContext) {
        HashMap<String,Object> extraContext = new HashMap<String,Object>();
        extraContext.put(ActionContext.PARAMETERS, new HashMap(parameterMap));
        extraContext.put(ActionContext.SESSION, sessionMap);
        extraContext.put(ActionContext.APPLICATION, applicationMap);

        Locale locale;
        if (defaultLocale != null) {
            locale = LocalizedTextUtil.localeFromString(defaultLocale, request.getLocale());
        } else {
            locale = request.getLocale();
        }

        extraContext.put(ActionContext.LOCALE, locale);
        //extraContext.put(ActionContext.DEV_MODE, Boolean.valueOf(devMode));

        extraContext.put(StrutsStatics.HTTP_REQUEST, request);
        extraContext.put(StrutsStatics.HTTP_RESPONSE, response);
        extraContext.put(StrutsStatics.SERVLET_CONTEXT, servletContext);

        // helpers to get access to request/session/application scope
        extraContext.put("request", requestMap);
        extraContext.put("session", sessionMap);
        extraContext.put("application", applicationMap);
        extraContext.put("parameters", parameterMap);

        AttributeMap attrMap = new AttributeMap(extraContext);
        extraContext.put("attr", attrMap);

        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();
        //设置ActionContext，把ActionInvocation和Action压入ValueStack
        ActionContext actionContext = ActionContext.getContext();

        if(actionContext != null) {
            actionContext.setActionInvocation(this);
        }
        //创建Action，可以看出Struts2里是每次请求都新建一个Action，careateAction方法可以自己参考
        createAction(contextMap);
        if (pushAction) {
            stack.push(action);
            contextMap.put("action", action);
        }
        invocationContext = new ActionContext(contextMap);
        invocationContext.setName(proxy.getActionName());
        List interceptorList = new ArrayList(proxy.getConfig().getInterceptors());
        interceptors = interceptorList.iterator();
    }
    protected void createAction(Map contextMap) {

        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);
        }
         ....... 
         catch (Exception e) {
            ........
            throw new XWorkException(gripe, e, proxy.getConfig());
        } 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();
            }

            if (!executed) {
                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Action对应的方法
                method = getAction().getClass().getMethod(methodName, new Class[0]);
            } catch (NoSuchMethodException e) {

                try {
                    //如果没有对应的方法，则使用do+Xxxx来再次获得方法
                    String altMethodName = "do" + methodName.substring(0, 1).toUpperCase() + methodName.substring(1);
                    method = getAction().getClass().getMethod(altMethodName, new Class[0]);
                } catch (NoSuchMethodException e1) {
                    .....
                }
            }
            
            if (!methodCalled) {
                methodResult = method.invoke(action, new Object[0]);
            }
            //根据不同的Result类型返回不同值
            if (methodResult instanceof Result) {
                this.explicitResult = (Result) methodResult;
                return null;
            } else {
                return (String) methodResult;
            }
        }
        ....
        } 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);
        reflectionProvider.setProperties(resultConfig.getParams(), result, extraContext);

        if (result instanceof Result)
            return (Result) result;
        throw new ConfigurationException(result.getClass().getName() + " does not implement Result.");
    }



    最后的时序图我拷贝开头url里那位作者的图吧。

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