Struts2源码解析（转载）

1) StrutsPrepareAndExecuteFilter
struts2以后web.xml的配置已经由配置servlet变成配置filter了



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

        HttpServletRequest request = (HttpServletRequest) req;  // 请求
        HttpServletResponse response = (HttpServletResponse) res; //响应

        try {
            prepare.setEncodingAndLocale(request, response);  //设置编码和语言
            prepare.createActionContext(request, response);  //创建当前线程的ActionContext
            prepare.assignDispatcherToThread(); //将dispatcher赋给当前线程
            if ( excludedPatterns != null && prepare.isUrlExcluded(request, excludedPatterns)) {
                chain.doFilter(request, response);   //如果该URL被exclude掉，继续chaining
            } else {
                request = prepare.wrapRequest(request); //包装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); // hit! 将请求交给dispatcher，触发其serviceAction方法(dispatcher.serviceAction(request, response, servletContext, mapping);)
                }
            }
        } finally {
            prepare.cleanupRequest(request);
        }
    }



2) Dispatcher
struts中的核心类，构造actionproxy以及actioninvocation，加载action类并调用其方法



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);
        boolean nullStack = stack == null;
        if (nullStack) {
            ActionContext ctx = ActionContext.getContext();
            if (ctx != null) {
                stack = ctx.getValueStack();
            }
        }

        if (stack != null) {

            //将值栈put进extraContext
            extraContext.put(ActionContext.VALUE_STACK, valueStackFactory.createValueStack(stack));
        }

        String timerKey = "Handling request from Dispatcher";
        try {
            UtilTimerStack.push(timerKey);
            String namespace = mapping.getNamespace();  // action名空间
            String name = mapping.getName();                    //action名称
            String method = mapping.getMethod();             //action方法

            Configuration config = configurationManager.getConfiguration();
            ActionProxy proxy = config.getContainer().getInstance(ActionProxyFactory.class).createActionProxy(
                    namespace, name, method, extraContext, true, false);  //创建actionproxy以及actioninvocation

            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();  //hit! 执行对应action的方法(默认proxy实现是StrutsActionProxy)             }

            // 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) {
            sendError(request, response, context, HttpServletResponse.SC_INTERNAL_SERVER_ERROR, e);
        } finally {
            UtilTimerStack.pop(timerKey);
        }
    }

3)StrutsActionProxy
struts中action的代理类



    public String execute() throws Exception {
        ActionContext previous = ActionContext.getContext();
        ActionContext.setContext(invocation.getInvocationContext());
        try {
// This is for the new API:
//            return RequestContextImpl.callInContext(invocation, new Callable<String>() {
//                public String call() throws Exception {
//                    return invocation.invoke();
//                }
//            });

            return invocation.invoke();  // 调用actioninvocation(默认实现是DefaultActionInvocation)         } finally {
            if (cleanupContext)
                ActionContext.setContext(previous);
        }
    }



4) DefaultActionInvocation
可以理解为承载action拦截器和action实例的容器，负责调用拦截器以及action的方法并将结果拼装起来


public String invoke() throws Exception {
        String profileKey = "invoke: ";
        try {
            UtilTimerStack.push(profileKey);

            if (executed) { //判断当前的状态
                throw new IllegalStateException("Action has already executed");
            }
            //loop拦截器并执行
            if (interceptors.hasNext()) {
                final InterceptorMapping interceptor = (InterceptorMapping) interceptors.next();
                String interceptorMsg = "interceptor: " + interceptor.getName();
                UtilTimerStack.push(interceptorMsg);
                try {

                      //每个拦截器的实现最后都会调用一次invocation.invoke();从而实现了链式调用(chaining)
                      resultCode = interceptor.getInterceptor().intercept(DefaultActionInvocation.this);
                }
                finally {
                    UtilTimerStack.pop(interceptorMsg);
                }
            } else {
                resultCode = invokeActionOnly();  //chaining的最后一步，调用action的方法
            }            // 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) {
                if (preResultListeners != null) {
                    for (Object preResultListener : preResultListeners) {
                        PreResultListener listener = (PreResultListener) preResultListener;

                        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();  //执行结果
                }

                executed = true;
            }

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




    private void executeResult() throws Exception {
        result = createResult();   //根据配置创建result,result种类很多, actionchainresult、httpheaderresult、freemarkerresult等

        String timerKey = "executeResult: " + getResultCode();
        try {
            UtilTimerStack.push(timerKey);
            if (result != null) {

                //根据结果类型，将数据以及view拼装起来，返回至前台
                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);
        }
    }