Apache Struts 2 Documentation Big Picture

http://struts.apache.org/docs/big-picture.html 

1. HttpServletRequest 穿越各个过滤器到达FilterDispatcher(这个已经不再使用，现在使用StrutsPrepareAndExecuteFilter）

2. 执行doFilter方法，如果模式不匹配，则进入下一个过滤链

3. 如果匹配则创建上下文（为每个请求创建实例，线程安全）

4. 根据ActionMapping 判断是否应该调用Action

5. 如果需要调用Action则把控制委派给ActionProxy

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

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

        try {
            if (excludedPatterns != null && prepare.isUrlExcluded(request, excludedPatterns)) {
                chain.doFilter(request, response);
            } else {
                prepare.setEncodingAndLocale(request, response);
                prepare.createActionContext(request, response);
                prepare.assignDispatcherToThread();
                request = prepare.wrapRequest(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);
                }
            }
        } finally {
            prepare.cleanupRequest(request);
        }
    }

6. 查询配置文件

7. 创建ActionInvocation ，它与拦截器的关系如下：

 /**
     * Override to handle interception
     */
    public abstract String intercept(ActionInvocation invocation) throws Exception;

8.调用拦截器栈、action类

9. action返回结果，有可能渲染jsp等模板，其中会发起额外的请求

10. 渲染完毕调用拦截器栈

11. HttpServletResponse通过过滤器

12. client得到响应