Spring boot @ModelAttribute标注的实现

@modelattribute可以注释方法和参数

@modelattribute注释方法

@modelattribute注释方法该方法会在controller的所有方法之前被执行。通过Model将value设定到相应的key中。

(1)注释返回值为void的方法，通过传入Model添加属性值

@RestController
@RequestMapping("/usrcontroller")
public class UserController {

  UserService us = new UserService();

  @modelattribute
  public void findUserById(@RequestParam Long uid,Model model) {
    model.addAttribute("user",us.getUser(uid));
  }

  @GetMapping(path="/getuser")
  @ResponseBody
  public String getUser(Model model) {
    User u = (User)(model.getAttribute("user"));
    System.out.println(u.name);
    return u.name;
  }
}

(2)注释返回值为具体类型的。通过添加属性（属性名为返回值的头字母小写,例如返回值为Group，属性为group）将返回值添加
实际结果类似与model.addAttribute("returnvaluename",var);

@RestController
@RequestMapping("/groupcontroller")
public class GroupController {
  @modelattribute
  public Group getGroupId(@RequestParam Long gid) {
    Group g = new Group();
    g.groupName = "group_"+gid;
    g.groupId = gid;

    return g;
    //same as Model.addAttribute("group",g)
  }

  @GetMapping(path="/getgroup")
  @ResponseBody
  public String getGroup(Model model) {
    Group g = (Group)model.getAttribute("group");
    String gStr = "group(id:" + g.groupId + "," + g.groupName + ")";
    System.out.println(gStr);

    return gStr;
  }
}

(3)指定属性的名称

//类似于Model.addAttribute("defaultuser",User)
@modelattribute("defaultuser")
public User createDefaultUser() {
  return new User("defaultUsr","SH",22,true);
}

@GetMapping(path="/checkdefaultuser")
@ResponseBody
public String checkDefaultUser(@modelattribute("defaultuser") User dfUsr) {
  String dfUsrStr = "Default user("+dfUsr.name + "," + dfUsr.address + "," + dfUsr.age + "," + dfUsr.isMan + ")";

  System.out.println(dfUsrStr);

  return dfUsrStr;
}

@ModeAttribute注释方法的参数

@modelattribute("defaultuser")
public User createDefaultUser() {
  return new User("defaultUsr"," + dfUsr.isMan + ")";
  System.out.println(dfUsrStr);
  return dfUsrStr;
}

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