springMVC--HandlerAdapter

HandlerAdapter的接口中定义了三个方法：

（1）boolean supports(Object handler); 判断是否支持传入的Handler

（2）ModelAndView handle(HttpServletRequest request, HttpServletResponse response, Object handler)  用来使用Handler处理请求

（3）long getLastModified(HttpServletRequest request, Object handler); 用来获取资料的Last-Modified值。

接口源码如下：

public interface HandlerAdapter {        boolean supports(Object handler);        ModelAndView handle(HttpServletRequest request, HttpServletResponse response, Object handler) throws Exception;        long getLastModified(HttpServletRequest request, Object handler);    }  

HandlerAdapter的执行操作，其执行过程在DispatcherServlet的doDispatch中，执行流程如下：

protected void doDispatch(HttpServletRequest request, HttpServletResponse response) throws Exception {                    ........            try {                            try {                                    //获取合适的HandlerAdapter实现类                  HandlerAdapter ha = getHandlerAdapter(mappedHandler.getHandler());                                ........                                    if (isGet || "HEAD".equals(method)) {                      long lastModified = ha.getLastModified(request, mappedHandler.getHandler());                                        }              ........                  //执行真正的请求操作                  mv = ha.handle(processedRequest, response, mappedHandler.getHandler());            ........      }  

getHandlerAdapter的操作就是选择合适的HandlerAdapter来执行，设计模式中的适配器模式，handlerAdapters中的内容就是所有的HandlerAdapter的实现类。

protected HandlerAdapter getHandlerAdapter(Object handler) throws ServletException {          for (HandlerAdapter ha : this.handlerAdapters) {              if (logger.isTraceEnabled()) {                  logger.trace("Testing handler adapter [" + ha + "]");              }              if (ha.supports(handler)) {                  return ha;              }          }          throw new ServletException("No adapter for handler [" + handler +                  "]: The DispatcherServlet configuration needs to include a HandlerAdapter that supports this handler");      }  

这样就完成了Handler的真正调用过程，最终调用过程是返回一个ModelAndView对象。