Struts2 框架执行流程

- Title: Struts2 框架执行流程
- Link: http://sh3ll.me/archives/201703141928.txt
- Published: 2017-03-14 19:28
- Updated: 2017-03-14 19:28

1. 容器（Tomcat）接收到用户发送的请求：http://sh3ll.local/demo.action，选择处理该请求的应用。

2. 容器读取应用的 web.xml，在其中查找 filter-mapping，根据 Filter 的配置找到 org.apache.struts2.dispatcher.FilterDispatcher，
回调 doFilter 方法，进行真正的处理。

3. FilterDispatcher 将请求转发给 ActionMapper，ActionMapper 负责判断当前请求是否需要 Struts2 进行处理 struts2-core-2.0.6.jar!/org/apache/struts2/dispatcher/FilterDispatcher.class：

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

        try {
            UtilTimerStack.push(timerKey);
            request = this.prepareDispatcherAndWrapRequest(request, response);

            ActionMapping mapping;
            try {
                mapping = actionMapper.getMapping(request, this.dispatcher.getConfigurationManager());
            } catch (Exception var20) {
                LOG.error("error getting ActionMapping", var20);
                this.dispatcher.sendError(request, response, servletContext, 500, var20);
                ActionContextCleanUp.cleanUp(req);
                return;
            }

            if(mapping == null) {
                ... snip ...
                if(serveStatic && resourcePath.startsWith("/struts")) {
                // Struts2 静态资源
                    String name = resourcePath.substring("/struts".length());
                    this.findStaticResource(name, request, response);
                } else {
                    // 不需要 Struts2 处理，继续上层调用链处理
                    chain.doFilter(request, response);
                }
            } else {
                try {
                    // 通知 FilterDispatcher 处理此请求
                    this.dispatcher.serviceAction(request, response, servletContext, mapping);
                } finally {
                    ActionContextCleanUp.cleanUp(req);
                }
            }
        ... snip ...
    }

4. 创建 ActionProxy 实例，作为 Action 与 xwork 的中间层，代理 Action 的运行过程 struts2-core-2.0.6.jar!/org/apache/struts2/dispatcher/Dispatcher.class：

    public void serviceAction(HttpServletRequest request, HttpServletResponse response, ServletContext context, ActionMapping mapping) throws ServletException {
        ... snip ...
        try {
            ... snip ...
            String method = mapping.getMethod();
            // 读取配置文件获取具体 Action
            Configuration config = this.configurationManager.getConfiguration();
            ActionProxy proxy = ((ActionProxyFactory)config.getContainer().getInstance(ActionProxyFactory.class)).createActionProxy(e, name, extraContext, true, false);
            proxy.setMethod(method);
            request.setAttribute("struts.valueStack", proxy.getInvocation().getStack());
            if(mapping.getResult() != null) {
                Result result = mapping.getResult();
                result.execute(proxy.getInvocation());
            } else {
                proxy.execute();
            }

        ... snip ...
    }
    
5. 创建 ActionInvocation 对象并进行调用。在调用用户层代码的前后要进行拦截器的调用（前后顺序相反） xwork-2.0.1.jar!/com/opensymphony/xwork2/DefaultActionInvocation.class：

    public String invoke() throws Exception {
        String profileKey = "invoke: ";

        String iterator2;
        try {
            UtilTimerStack.push(profileKey);
            if(this.executed) {
                throw new IllegalStateException("Action has already executed");
            }

            if(this.interceptors.hasNext()) {
                final InterceptorMapping iterator = (InterceptorMapping)this.interceptors.next();
                UtilTimerStack.profile("interceptor: " + iterator.getName(), new ProfilingBlock() {
                    public String doProfiling() throws Exception {
                        DefaultActionInvocation.this.resultCode = iterator.getInterceptor().intercept(DefaultActionInvocation.this);
                        return null;
                    }
                });
            } else {
                this.resultCode = this.invokeActionOnly();
            }

            if(!this.executed) {
                if(this.preResultListeners != null) {
                    Iterator iterator1 = this.preResultListeners.iterator();

                    while(iterator1.hasNext()) {
                        PreResultListener listener = (PreResultListener)iterator1.next();
                        String _profileKey = "preResultListener: ";

                        try {
                            UtilTimerStack.push(_profileKey);
                            listener.beforeResult(this, this.resultCode);
                        } finally {
                            UtilTimerStack.pop(_profileKey);
                        }
                    }
                }

                if(this.proxy.getExecuteResult()) {
                    this.executeResult();
                }

                this.executed = true;
            }

            iterator2 = this.resultCode;
        } finally {
            UtilTimerStack.pop(profileKey);
        }

        return iterator2;
    }

6. 调用用户层代码 Action 的 execute 方法，根据其返回结果去配置文件中选择结果页面（view 层）进行渲染，生成最终页面。

7. ActionInvocation 对象执行完毕后，将得到的响应对象展示给客户端。