Spring MVC之 HandlerAdapter
实际上就是根据HandlerAdapter找到的Controller,调用相应的方法,其中数据转换、数据格式化、数据验证就需要相应的适配器去做。
HandlerAdapter 接口实现:
HttpRequestHandlerAdapter : 要求handler实现HttpRequestHandler接口,
该接口的方法为: void handleRequest(HttpServletRequest request, HttpServletResponse response)也就是 handler必须有一个handleRequest方法
SimpleControllerHandlerAdapter:要求handler实现Controller接口,该接口的方法为ModelAndView handleRequest(HttpServletRequest request, HttpServletResponse response),也就是本工程采用的
AnnotationMethodHandlerAdapter:和上面的DefaultAnnotationHandlerMapping配对使用的,也已过时
RequestMappingHandlerAdapter:和上面的RequestMappingHandlerMapping配对使用,针对@RequestMapping
HandlerAdapter原理
其实HandlerAdapter就是一堆适配的规范接口,找到对应的适配器后,就能将Spring框架和我们自定义的controller连接起来。
代码例子:
定义一个Adapter接口
public interface HandlerAdapter {
public boolean supports(Object handler);
public void handle(Object handler);
}
以下是三种Controller实现
public interface Controller {
}
public class HttpController implements Controller{
public void doHttpHandler(){
System.out.println("http...");
}
}
public class SimpleController implements Controller{
public void doSimplerHandler(){
System.out.println("simple...");
}
}
public class AnnotationController implements Controller{
public void doAnnotationHandler(){
System.out.println("annotation...");
}
}
下面编写适配器类
public class SimpleHandlerAdapter implements HandlerAdapter {
public void handle(Object handler) {
((SimpleController)handler).doSimplerHandler();
}
public boolean supports(Object handler) {
return (handler instanceof SimpleController);
}
}
public class HttpHandlerAdapter implements HandlerAdapter {
public void handle(Object handler) {
((HttpController)handler).doHttpHandler();
}
public boolean supports(Object handler) {
return (handler instanceof HttpController);
}
}
public class AnnotationHandlerAdapter implements HandlerAdapter {
public void handle(Object handler) {
((AnnotationController)handler).doAnnotationHandler();
}
public boolean supports(Object handler) {
return (handler instanceof AnnotationController);
}
}
模拟一个DispatcherServlet
import java.util.ArrayList;
import java.util.List;
public class DispatchServlet {
public static List<HandlerAdapter> handlerAdapters = new ArrayList<HandlerAdapter>();
public DispatchServlet(){
handlerAdapters.add(new AnnotationHandlerAdapter());
handlerAdapters.add(new HttpHandlerAdapter());
handlerAdapters.add(new SimpleHandlerAdapter());
}
public void doDispatch(){
//此处模拟SpringMVC从request取handler的对象,仅仅new出,可以出,
//不论实现何种Controller,适配器总能经过适配以后得到想要的结果
// HttpController controller = new HttpController();
// AnnotationController controller = new AnnotationController();
SimpleController controller = new SimpleController();
//得到对应适配器
HandlerAdapter adapter = getHandler(controller);
//通过适配器执行对应的controller对应方法
adapter.handle(controller);
}
public HandlerAdapter getHandler(Controller controller){
for(HandlerAdapter adapter: this.handlerAdapters){
if(adapter.supports(controller)){
return adapter;
}
}
return null;
}
public static void main(String[] args){
new DispatchServlet().doDispatch();
}
}
参考:
https://zhidao.baidu.com/question/136290865875605525.html