@ModelAttribute和@SessionAttributes和@SessionAttribute和@RequestAttribute-CFANZ编程社区

一、@ModelAttribute

用法

代码例子

abstract public class CommonController {
    @ModelAttribute
    public void  MyModelAttribute(Model model){
        model.addAttribute("model", "MyModel");
    }
    @ModelAttribute
    public void newUser(Model model){
        User user = new User();
        user.setName("myUser");
        user.setId(1);
        model.addAttribute("myUser", user);
    }
}

@Controller
public class MyController  {  
    @RequestMapping("init")
    @ResponseBody
    public String init(){
        return "init";
    }
    @RequestMapping("user")
    @ResponseBody
    public void getUser(@ModelAttribute("myUser")User user){
        System.out.println(user.toString());
    }
    @ModelAttribute("modelAndMapping")
    @RequestMapping("yes")
    public String modelAttributeAndRequestMapping(){
        return "yes1";
    }
}

yes.jsp

<%@ page contentType="text/html;charset=UTF-8" language="java" %>
<html>
<head>
    <title>yes.jsp</title>
</head>
<body>
${modelAndMapping}
</body>
</html>

二、@SessionAttributes和@SessionAttribute

作用：作用是将指定的Model中的键值对添加至session中，方便在下一次请求中使用该注解只能作用与类上。
@SessionAttributes注解设置的参数有3类方式去使用它：

//通过 @SessionAttributes 注解将Model中attrName为 "user","id","name" 的值添加至 session 中
@SessionAttributes(value = {"user","id","name"})
@Controller
public class UserController {
    @ModelAttribute("user")
    public User login(){
        User user = new User();
        user.setName("loginYES");
        user.setId(2);
        return user;
    }
    @RequestMapping("newUser")
    public String testHandler(Model model){
        model.addAttribute("id",23);
        model.addAttribute("name","kk");
        return "result";
    }
    @ResponseBody
    @RequestMapping("iisLogin")
    //通过@SessionAttribute来获取，则正常获取到
    public String isLogin(@ModelAttribute("user") User user) {
        if (user.getName() != null) {
            return "isLogin!";
        } else return "isLogin??";
    }
}

@Controller
public class MyController {
    @ResponseBody
    @RequestMapping("isLogin")
    public String isLogin(@ModelAttribute("user") User user,HttpSession httpSession){
        if(user.getName()!=null){
            return "isLogin!";
        }
        else return "isLogin??";
    }
}

result.jsp

<%@ page contentType="text/html;charset=UTF-8" language="java" %>
<html>
<head>
    <title>result</title>
</head>
<body>
${sessionScope.user.id}
${sessionScope.user.name}
<br/>
${sessionScope.id}
${sessionScope.name}
</body>
</html>

在这里插入图片描述

@SessionAttributes 是将model设置到session中去。
@SessionAttribute 是从session获取之前设置到session中的数据。

四、@RequestAttribute

作用：用在方法入参上，从request中取对应的值，至于request中是怎么存在该属性的，方式多种多样，拦截器中预存、ModelAttribute注解预存、请求转发带过来的。

尝试访问一个request中不存在的值时，@RequestAttribute抛出异常：

@RequestMapping("/demo1")
    public String demo1(@RequestAttribute String name){
        System.out.println(name);
        return "test";
    }

请求request中预存属性的方式：

方式一.ModelAttribute注解

@ModelAttribute
public void storeEarly(HttpServletRequest request){
    request.setAttribute("name","lvbinbin");
}

方式二.拦截器中request.setAttribute()

public class SimpleInterceptor implements HandlerInterceptor {

    @Override
    public boolean preHandle(HttpServletRequest request, HttpServletResponse response, Object handler) throws Exception {
        System.out.println(" Simple Interceptor preHandle");
        request.setAttribute("name",24);
        return true;
    }

    @Override
    public void postHandle(HttpServletRequest request, HttpServletResponse response, Object handler, ModelAndView modelAndView) throws Exception {
        System.out.println(" Simple Interceptor postHandle");
    }

    @Override
    public void afterCompletion(HttpServletRequest request, HttpServletResponse response, Object handler, Exception ex) throws Exception {
        System.out.println(" Simple Interceptor afterCompletion");
    }
}

方式三.请求转发，转发过来的请求属性中存在；

@RequestAttribute属性required

@RequestAttribute属性required默认为true, request.getAttribute获取不到参数就会抛出异常 ServletRequestBindingException ；当 required设置为false，即使没有从request中获取到就忽略跳过，赋值为null;

@RequestAttribute和@RequestParam和@RequestBody

参考文章