Struts2执行流程源码解析

这个是过去版本的，但是大致执行流程是大同小异的。
首先struts2的入口就是，StrutsPrepareAndExecuteFilter，核心过滤器

首先会执行过滤器的init初始化方法

 public void init(FilterConfig filterConfig) throws ServletException {
     //初始化操作类
        InitOperations init = new InitOperations();
        Dispatcher dispatcher = null;
        try {
            FilterHostConfig config = new FilterHostConfig(filterConfig);

            init.initLogging(config);
             //初始化分发器
            dispatcher = init.initDispatcher(config);
            //初始化静态资源加载器
            init.initStaticContentLoader(config, dispatcher);
        //初始化进行Http预处理的操作类
            prepare = new PrepareOperations(filterConfig.getServletContext(), dispatcher);
           //初始化进行Http请求处理的逻辑执行的操作类
            execute = new ExecuteOperations(filterConfig.getServletContext(), dispatcher);
            this.excludedPatterns = init.buildExcludedPatternsList(dispatcher);
            //自定义初始化过程，留待扩展
            postInit(dispatcher, filterConfig);
        } finally {
            if (dispatcher != null) {
                dispatcher.cleanUpAfterInit();
            }
            //初始化之中的清理工作
            init.cleanup();
        }
    }

然后会跳转到doFilter()

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

        HttpServletRequest request = (HttpServletRequest) req;
        HttpServletResponse response = (HttpServletResponse) res;

        try {
            //设置编码集
            prepare.setEncodingAndLocale(request, response);
            //创建ActionContext,ValueStack等
            prepare.createActionContext(request, response);
            //获取当前线程
            prepare.assignDispatcherToThread();
            if (excludedPatterns != null && prepare.isUrlExcluded(request, excludedPatterns)) {
                chain.doFilter(request, response);
            } else {
            //包装request
                request = prepare.wrapRequest(request);
                //获取action，里面有切割uri的过程
                ActionMapping mapping = prepare.findActionMapping(request, response, true);
                if (mapping == null) {
                    boolean handled = execute.executeStaticResourceRequest(request, response);
                    if (!handled) {
                        chain.doFilter(request, response);
                    }
                } else {
                //执行action,这也是struts2的核心部分
                    execute.executeAction(request, response, mapping);
                }
            }
        } finally {
        //清理request，ActionContext，Dispatcher等
            prepare.cleanupRequest(request);
        }
    }

下面对execute.executeAction(request, response, mapping); 这个方法，进行源码分析。

点击进去进入ExecuteOperations类的executeAction()，只是个跳转。

  public void executeAction(HttpServletRequest request, HttpServletResponse response, ActionMapping mapping) throws ServletException {
        dispatcher.serviceAction(request, response, servletContext, mapping);
    }

点击serviceAction方法，进入Dispatcher类，也就是核心分发器。

 public void serviceAction(HttpServletRequest request, HttpServletResponse response, ServletContext context,
                              ActionMapping mapping) throws ServletException {
        //创建Context
        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) {
        //将ActionContext放置于ThreadLocal中，创建线程副本，使其线程安全。
            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);
            String namespace = mapping.getNamespace();
            String name = mapping.getName();
            String method = mapping.getMethod();

            Configuration config = configurationManager.getConfiguration();
            //创建代理对象并且获取
            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 (!nullStack) {
                request.setAttribute(ServletActionContext.STRUTS_VALUESTACK_KEY, stack);
            }
        } catch (ConfigurationException e) {
            // WW-2874 Only log error if in devMode
            if (devMode) {
                String reqStr = request.getRequestURI();
                if (request.getQueryString() != null) {
                    reqStr = reqStr + "?" + request.getQueryString();
                }
                LOG.error("Could not find action or result\n" + reqStr, e);
            } else {
                if (LOG.isWarnEnabled()) {
                    LOG.warn("Could not find action or result", e);
                }
            }
            sendError(request, response, context, HttpServletResponse.SC_NOT_FOUND, e);
        } catch (Exception e) {
            if (handleException || devMode) {
                sendError(request, response, context, HttpServletResponse.SC_INTERNAL_SERVER_ERROR, e);
            } else {
                throw new ServletException(e);
            }
        } finally {
            UtilTimerStack.pop(timerKey);
        }
    }

点击createActionProxy()方法，进入DefaultActionProxyFactory，action代理工厂

  public ActionProxy createActionProxy(String namespace, String actionName, String methodName, Map<String, Object> extraContext, boolean executeResult, boolean cleanupContext) {

        ActionInvocation inv = new DefaultActionInvocation(extraContext, true);
        container.inject(inv);
        return createActionProxy(inv, namespace, actionName, methodName, executeResult, cleanupContext);
    }

点击createActionProxy方法

  public ActionProxy createActionProxy(ActionInvocation inv, String namespace, String actionName, String methodName, boolean executeResult, boolean cleanupContext) {

        DefaultActionProxy proxy = new DefaultActionProxy(inv, namespace, actionName, methodName, executeResult, cleanupContext);
        container.inject(proxy);
        proxy.prepare();
        return proxy;
    }

点击prepare()方法，进入DefaultActionProxy类

protected void prepare() {
        String profileKey = "create DefaultActionProxy: ";
        try {
            UtilTimerStack.push(profileKey);
            config = configuration.getRuntimeConfiguration().getActionConfig(namespace, actionName);

            if (config == null && unknownHandlerManager.hasUnknownHandlers()) {
                config = unknownHandlerManager.handleUnknownAction(namespace, actionName);
            }
            if (config == null) {
                throw new ConfigurationException(getErrorMessage());
            }

            resolveMethod();

            if (!config.isAllowedMethod(method)) {
                throw new ConfigurationException("Invalid method: " + method + " for action " + actionName);
            }
            //初始化
            invocation.init(this);

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

点击init()进入DefaultActionInvocation类

 public void init(ActionProxy proxy) {
        this.proxy = proxy;
        Map<String, Object> 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
        createAction(contextMap);

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

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

        //创建拦截器栈，并且用迭代器的方式迭代
        // get a new List so we don't get problems with the iterator if someone changes the list
        List<InterceptorMapping> interceptorList = new ArrayList<InterceptorMapping>(proxy.getConfig().getInterceptors());
        interceptors = interceptorList.iterator();
    }

点击createAction方法，在此处创建action的代理对象，源码深处是通过反射的方式获得的，在此不再赘述。

    protected void createAction(Map<String, Object> contextMap) {
        // load action
        String timerKey = "actionCreate: " + proxy.getActionName();
        try {
            UtilTimerStack.push(timerKey);
            action = objectFactory.buildAction(proxy.getActionName(), proxy.getNamespace(), proxy.getConfig(), contextMap);
        } catch (InstantiationException e) {
            throw new XWorkException("Unable to intantiate Action!", e, proxy.getConfig());
        } catch (IllegalAccessException e) {
            throw new XWorkException("Illegal access to constructor, is it public?", e, proxy.getConfig());
        } catch (Exception e) {
            String gripe;

            if (proxy == null) {
                gripe = "Whoa!  No ActionProxy instance found in current ActionInvocation.  This is bad ... very bad";
            } else if (proxy.getConfig() == null) {
                gripe = "Sheesh.  Where'd that ActionProxy get to?  I can't find it in the current ActionInvocation!?";
            } else if (proxy.getConfig().getClassName() == null) {
                gripe = "No Action defined for '" + proxy.getActionName() + "' in namespace '" + proxy.getNamespace() + "'";
            } else {
                gripe = "Unable to instantiate Action, " + proxy.getConfig().getClassName() + ",  defined for '" + proxy.getActionName() + "' in namespace '" + proxy.getNamespace() + "'";
            }

            gripe += (((" -- " + e.getMessage()) != null) ? e.getMessage() : " [no message in exception]");
            throw new XWorkException(gripe, e, proxy.getConfig());
        } finally {
            UtilTimerStack.pop(timerKey);
        }

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

返回来，执行Dispatcher类中的 proxy.execute();，执行DefaultActionProxy中的execute()，执行invoke()方法完成迭代，执行拦截器栈中的拦截器。

    public String execute() throws Exception {
        ActionContext nestedContext = ActionContext.getContext();
        ActionContext.setContext(invocation.getInvocationContext());

        String retCode = null;

        String profileKey = "execute: ";
        try {
            UtilTimerStack.push(profileKey);

            retCode = invocation.invoke();
        } finally {
            if (cleanupContext) {
                ActionContext.setContext(nestedContext);
            }
            UtilTimerStack.pop(profileKey);
        }

        return retCode;
    }

拦截器执行完毕后，执行结果集

 public void serviceAction(HttpServletRequest request, HttpServletResponse response, ServletContext context,
                              ActionMapping mapping) throws ServletException {
                         .....
            if (mapping.getResult() != null) {
                Result result = mapping.getResult();
                                    result.execute(proxy.getInvocation());
                 } else {
                 proxy.execute();
                 }
                 ....

结果集执行完毕后，完成跳转，通常是jsp页面或者Freemarker，Velocity等模板技术实现的页面。
最后，倒叙执行拦截器，执行核心过滤器的cleanupRequest方法清除request，ActionContext，Dispatcher中的内容，然后response返回浏览器。

} finally {
            prepare.cleanupRequest(request);
        }