Spring MVC之 HandlerAdapter

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

Spring MVC之 HandlerAdapter

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