springmvc中forward和redirect

一、跳转

import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import org.springframework.stereotype.Controller;
import org.springframework.web.bind.annotation.RequestMapping;  

@Controller
public class Login{  

        /**转发**/
    @RequestMapping("/login.do")
    public String login(HttpServletRequest request,HttpServletResponse   response){
        request.setAttribute("message", "hello");
        return "forward:/index.do";  //forward在跳转后可以取到message值
    }
    @RequestMapping("/index.do")
    public String index(HttpServletRequest request,HttpServletResponse   response){
        return "welcome";
    }  

    /**重定向**/
    @RequestMapping("/logout.do")
    public String logout(HttpServletRequest request,HttpServletResponse   response){
        request.setAttribute("message", "hello");
        return "redirect:/register.do";  //redirect在跳转后无法取到message值
    }
    @RequestMapping("/register.do")
    public String register(HttpServletRequest request,HttpServletResponse   response){
        return "register";
    }
}

　　另外forward跳转后地址栏URL不会改变 而redirect会改变

二、传参

@RequestMapping(value = "update", method = RequestMethod.POST)
    public String update(@Valid @ModelAttribute("user") User user,
                             RedirectAttributes redirectAttributes) {
        accountService.updateUser(user);
        redirectAttributes.addFlashAttribute("message", "更新用户" + user.getLoginName() + "成功");
        return "redirect:/admin/user";
    }

　　为了防止用户刷新重复提交，save操作之后一般会redirect到另一个页面，同时带点操作成功的提示信息。因为是Redirect，Request里的attribute不会传递过去，如果放在session中，则需要在显示后及时清理，不然下面每一页都带着这个信息也不对。Spring在3.1才提供了这个能力，原理是放到session中，session在跳到页面后马上移除对象。所以你刷新一下后这个值就会丢掉。