springmvc 实现Controller控制器的三种实现方式，注解、实现HttpRequestHandler接口、实现Controller接口源码分析

springmvc实现前端控制器的三种实现方法：

1、使用注解@Controller

2、实现HttpRequestHandler接口

这种方式需要配置适配器HttpRequestHandlerAdapter，交给适配来执行

springmvc.xml

 
       
         
       
       
       
       
       

前端控制器编写：

public class LoginController implements HttpRequestHandler{

    public void handleRequest(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        System.out.println("HttpRequestHandler.........");
        //为返回页面设置数据
        request.setAttribute("name", "akld");
        //设置返回页面
        request.getRequestDispatcher("/index.jsp").forward(request, response);
    }

}

HttpRequestHandler接口

public interface HttpRequestHandler {

    /**
     * Process the given request, generating a response.
     * @param request current HTTP request
     * @param response current HTTP response
     * @throws ServletException in case of general errors
     * @throws IOException in case of I/O errors
     */
    void handleRequest(HttpServletRequest request, HttpServletResponse response)
            throws ServletException, IOException;

}

HttpRequestHandler实现类HttpRequestHandlerAdapter适配器

public class HttpRequestHandlerAdapter implements HandlerAdapter {

 

    @Override
    public boolean supports(Object handler) {

       //supports方法本质上就是判断handler是否是Servlet
        return (handler instanceof HttpRequestHandler);
    }

    //handle本质上是执行HttpRequestHandler.handleRequest方法

    @Override
    public ModelAndView handle(HttpServletRequest request, HttpServletResponse response, Object handler)
            throws Exception {

        ((HttpRequestHandler) handler).handleRequest(request, response);
        return null;
    }

    @Override
    public long getLastModified(HttpServletRequest request, Object handler) {
        if (handler instanceof LastModified) {
            return ((LastModified) handler).getLastModified(request);
        }
        return -1L;
    }

}
3、实现Controller接口

public class HttpController implements Controller{

    public ModelAndView handleRequest(HttpServletRequest request, HttpServletResponse response) throws Exception {
        System.out.println("Controller.........");
        return new ModelAndView("index");
    }

}

Controller接口：

public interface Controller {

    /**
     * Process the request and return a ModelAndView object which the DispatcherServlet
     * will render. A {@code null} return value is not an error: it indicates that
     * this object completed request processing itself and that there is therefore no
     * ModelAndView to render.
     * @param request current HTTP request
     * @param response current HTTP response
     * @return a ModelAndView to render, or {@code null} if handled directly
     * @throws Exception in case of errors
     */
    ModelAndView handleRequest(HttpServletRequest request, HttpServletResponse response) throws Exception;

}

SimpleControllerHandlerAdapter适配器：

public class SimpleControllerHandlerAdapter implements HandlerAdapter {

    @Override
    public boolean supports(Object handler) {
        return (handler instanceof Controller);
    }

    @Override
    public ModelAndView handle(HttpServletRequest request, HttpServletResponse response, Object handler)
            throws Exception {

        return ((Controller) handler).handleRequest(request, response);
    }

    @Override
    public long getLastModified(HttpServletRequest request, Object handler) {
        if (handler instanceof LastModified) {
            return ((LastModified) handler).getLastModified(request);
        }
        return -1L;
    }

}

supports方法就是判断handler是否是Servlet

getLastModified直接返回modified值

handle方法本质是执行HttpRequestHandler.handleRequest方法。

开发过程中，用的比较多还是直接用注解的方式，简单快速开发。非注解方式的处理器映射器和处理器适配器可以同时存在多个。非注解方式的处理器映射器和处理器适配器之间可以混用。