Struts2 框架执行流程

  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 ...
}
  1. 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 ...
}
  1. 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;
}

  1. 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。

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