controller传值view

400错误是请求错误

Model是map格式

@Controller
public class HelloController {
    //view的值传给controller
    @RequestMapping(value="/t04")
   //public String welcome(@RequestParam(value="username",required=false) String username){
    public String welcome(String username,Model model ){
        System.out.println("以后靠你了"+username);
        model.addAttribute("username",username);
　　　　//model.addAttribute(username);--输出页面就得改为${string}
        return "index";
    }
}

model的作用域是request的级别

访问：http://localhost:8080/springmvc2/t04?username=hanlu

输出页面+ <h1>${username }</h1>

@RequestMapping(value="/hello2")
    public ModelAndView hello(String username){
        System.out.println("hello2----");
        ModelAndView model = new ModelAndView();
        model.setViewName("index");
        model.addObject("username", username);
        return model;
    }

访问页面：http://localhost:8080/springmvc2/hello2?username=hanlu

如果是对象的话model.addObject("user", new User());

model.addObject("username", username);改model.addObject(username);时要将
输出页面+ <h1>${username }</h1>改为${string}
//注意string要小写
下面还有一种方法“不推荐使用，可以了解了解

//不推荐使用
    @RequestMapping(value="/hello3")
    public String hello(String username,Map<String,Object> model){
        System.out.println("hello3---");
        model.put("username", username);//输出页面${username}
        return "index";
    }

如果有2个model的话，后面的model会覆盖前面的model。因为取到的都是同一个key，如果想不一样就把key的变不一样

使用JSTL标签实现页面输出（就是c标签）

1、添加jar包

2、在输出的页面加入<%@taglib prefix="c" uri="http://java.sun.com/jsp/jstl/core" %>

3、输出的参数： <c:out value="${username }"></c:out>

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