springMVC数据模型model,modelmap,map,@ModelAttribute的相互关系

结论:

a.注解方法中形参为model,modelmap,map一个或几个时，他们指向的引用对象相同即他们的值相同。

b.当使用@ModelAttribute注解请求参数时，springmvc自动将该参数放入model,modelmap,map中。

c.model,modelmap,map中put,request.setattribute(),b中@ModelAttribute以及modelandveiw.addObj()效果相同，return时都是将参数放request的attribute中。

d.model,modelmap,map，modelandview的生命同期仅存在于当前方法内，forward/return后重新生成新空对象。

e.当使用redirectAttribute.addFlashAttribute重定向时，FlashAttribute会自动注入下一个action内部model,modelmap,map，详细请参考https://www.cnblogs.com/pu20065226/p/10032048.html中的3.2model跟踪。

1.发送请求：http://localhost:8080/project/page/login/ModelTest/Map.do?aa=111&bb=333

@Controller
@RequestMapping("/page/login/ModelTest")
public class ModelTestController {
    @RequestMapping(value = "/Map.do")
    public String MapTest(HttpServletRequest request, Map<String, Object> map) {
        System.out.println("hello");
        System.out.println(map);
        map.put("step1", "step1");
        PrintRequestInfo.printSessionAndRequest(request, ModelTestController.class.getName());//打印
        map.put("step2", "step2");
        request.setAttribute("step3", "step3");
        final HttpSession session = request.getSession();
        session.setAttribute("step4", "step4");
        // return "../loginSuccess.jsp";
        return "Map1.do";

    }
}

输出：
hello
{}
================com..controller.ModelTestController====================
print  request parameter:
aa==111
bb==333
print  request attribute:

print  session parameter:
step4==step4

结论：map的初始值为空

2.当请求forward到第二个action（Map1.do）中

@RequestMapping(value = "/Map1.do")
    public String MapTest1(HttpServletRequest request, @ModelAttribute("aa") String aa,
            Map<String, Object> map, Model model) {
        System.out.println("welcome to MapTest1");
        model.addAttribute("mdbefore", "before");
        System.out.println(map);
        System.out.println("................");
        System.out.println(model.asMap());

        model.addAttribute("mdafter", "after");

        System.out.println("hello");
        System.out.println(map);
        System.out.println("................");
        System.out.println(model.asMap());

        PrintRequestInfo.printSessionAndRequest(request, ModelTestController.class.getName() + "1");
        // return "../loginSuccess.jsp";
        return "Map2.do";
    }

输出：

welcome to MapTest1
{aa=111, org.springframework.validation.BindingResult.aa=org.springframework.validation.BeanPropertyBindingResult: 0 errors, mdbefore=before}

................//aa由形参@ModelAttribute（“aa”）注入
{aa=111, org.springframework.validation.BindingResult.aa=org.springframework.validation.BeanPropertyBindingResult: 0 errors, mdbefore=before}
hello
{aa=111, org.springframework.validation.BindingResult.aa=org.springframework.validation.BeanPropertyBindingResult: 0 errors, mdbefore=before, mdafter=after}
................
{aa=111, org.springframework.validation.BindingResult.aa=org.springframework.validation.BeanPropertyBindingResult: 0 errors, mdbefore=before, mdafter=after}
================com.controller.ModelTestController1====================
print  request parameter:
aa==111
bb==333
print  request attribute:

step3==step3 //上一个action中map.put加入
step2==step2
step1==step1 //上一个action中request.setattribute加入

print  session parameter:
step4==step4

结论：

a.注解方法中形参为model,modelmap,map一个或几个时，他们指向的引用对象相同即他们的值相同。

b.当使用@ModelAttribute注解请求参数时，springmvc自动将该参数放入model,modelmap,map中。

3.当请求进入第三个action(Map2.do)时

@RequestMapping(value = "/Map2.do")
    public String MapTest2(HttpServletRequest request, Map<String, Object> map, Model model,
            ModelMap mm) {
        System.out.println("welcome to MapTest2");
        model.addAttribute("mdbefore2", "before2");
        System.out.println(map);
        System.out.println("................");
        System.out.println(model.asMap());
        System.out.println("................");
        System.out.println(mm);
        model.addAttribute("mdafter2", "after2");

        System.out.println("hello");
        System.out.println(map);
        System.out.println("................");
        System.out.println(model.asMap());

        PrintRequestInfo.printSessionAndRequest(request, ModelTestController.class.getName() + "2");
        return "../loginSuccess.jsp";
    }

输出结果：

welcome to MapTest2
{mdbefore2=before2}
................
{mdbefore2=before2}
................
{mdbefore2=before2}
hello
{mdbefore2=before2, mdafter2=after2}
................
{mdbefore2=before2, mdafter2=after2}
================com.controller.ModelTestController2====================
print  request parameter:
aa==111
bb==333
print  request attribute:

mdbefore==before//由上一个action中model.addAtrribute加入
step3==step3
step2==step2
step1==step1
mdafter==after//由上一个action中model.addAtrribute加入
aa==111 //aa由上一个action形参@ModelAttribute（“aa”）注入

print  session parameter:
step4==step4

结论：

c.model,modelmap,map中put,request.setattribute(),b中@ModelAttribute以及modelandveiw.addObj()效果相同（可以自己测试），return时都是将参数放request的attribute中。

d.model,modelmap,map，modelandview的生命同期仅存在于当前方法内，forward/return后重新生成新空对象

打印方法代码

public class PrintRequestInfo {
    public static void printSessionAndRequest(HttpServletRequest request, String remark) {
        System.out.println("================" + remark + "====================");
        System.out.println("print  request parameter:");
        final Enumeration reqEnum = request.getParameterNames();
        while (reqEnum.hasMoreElements()) {
            final String s = (String) reqEnum.nextElement();
            System.out.println(s + "==" + request.getParameter(s));
        }

        System.out.println("print  request attribute:");
        final Enumeration reqAttrs = request.getAttributeNames();
        while (reqAttrs.hasMoreElements()) {
            final String s = (String) reqAttrs.nextElement();
            System.out.println(s + "==" + request.getAttribute(s));
        }

        System.out.println("print  session parameter:");
        final HttpSession session = request.getSession();
        final Enumeration se = session.getAttributeNames();
        while (se.hasMoreElements()) {
            final String key = (String) se.nextElement();
            System.out.println(key + "==" + session.getAttribute(key));
        }
    }
}

原文地址：https://www.cnblogs.com/pu20065226/p/10076758.html