看透SpringMVC-源码分析与实践 - 9大组件 - HandlerAdapter

承上

映射器HandlerMapping是通过request找到Handler，而适配器HandlerAdapter则是实际使用Handler处理请求的



适配器HandlerAdapter只有5个直接实现

AbstractHandlerMethodAdapter，此系列两层，有子类RequestMappingHandlerAdapter

HttpRequestHandlerAdapter

SimpleControllerHandlerAdapter

AnnotationMethodHandlerAdapter - 弃用

SimpleServletHandlerAdapter

回顾HandlerAdapter接口，共有三个方法：

// 是否支持传入的Handler
boolean supports(Object handler);
// 使用Handler处理请求
ModelAndView handle(HttpServletRequest request, HttpServletResponse response, Object handler) throws Exception;
// 获取资源的Last-Modified
long getLastModified(HttpServletRequest request, Object handler);

HandlerAdapter的实现中，RequestMappingHandlerAdapter非常复杂，因为要处理的请求太灵活，Handler可以是任意的方法，没有任何约束，其中最**关键是参数的解析映射**

先说简单的：

HttpRequestHandlerAdapter：适配HttpRequestHandler

SimpleControllerHandlerAdapter：适配Controller

SimpleServletHandlerAdapter：适配Servlet

//org.springframework.web.servlet.mvc.HttpRequestHandlerAdapter
public ModelAndView handle(HttpServletRequest request, HttpServletResponse response, Object handler)
throws Exception {
((HttpRequestHandler) handler).handleRequest(request, response);
return null;
}
//org.springframework.web.servlet.handler.SimpleServletHandlerAdapter
public ModelAndView handle(HttpServletRequest request, HttpServletResponse response, Object handler)
throws Exception {
((Servlet) handler).service(request, response);
return null;
}
// org.springframework.web.servlet.mvc.SimpleControllerHandlerAdapter
public ModelAndView handle(HttpServletRequest request, HttpServletResponse response, Object handler)
throws Exception {
return ((Controller) handler).handleRequest(request, response);
}