我有两种模式： User,Project

public class Project{
    private int id;
    @NotEmpty(message="Project Name can not be empty")
    private String name;
    private User manager;
    private User operator;
    //getter/setter omitted
}

public class User{
    private int id;
    private String name;
    //omit other properties and getter/setter
}

现在，当我创建一个新项目时，我将向ProjectController提交以下参数：

projects?name=jhon&manager.id=1&operator.id=2...

然后，我将创建一个新的Project对象并将其插入db。

但是，我必须验证经理和操作员的ID是否有效，也就是说，我将验证用户表中是否存在匹配的ID。

所以我想知道如何实施这种验证？

---

update1：​​使用验证器

这是创建新项目的形式：

<sf:form method="${project.id==0?'post':'put'}" commandName="project" action="${context}${action}">
    Manager:<sf:input path="manager.id" />  <sf:errors path="manager.id" /> <br />
    Operator:<sf:input path="operator.id" />    <sf:errors path="operator.id" />    <br />
    Name:<sf:input path="name" />   <sf:errors path="name" />   <br />
    <input type="submit" value="Submit" />
</sf:form>


@Override
public void validate(Object obj, Errors errors) {
    User user = (User) obj;
    int id=user.getId();
    User u=userDao.query(id);
    if(u==null){
        errors.rejectValue("id", "user does not exist!");
    }
}

看来此验证器有效。

但是，错误消息不能显示在窗体中。

然后通过调试我检查了结果对象，发现了这一点：

org.springframework.validation.BeanPropertyBindingResult: 2 errors
Field error in object 'project' on field 'id': rejected value [0]; codes [user does not exist!.project.id,user does not exist!.id,user does not exist!.int,user does not exist!]; arguments []; default message [null]
Field error in object 'project' on field 'id': rejected value [0]; codes [user does not exist!.project.id,user does not exist!.id,user does not exist!.int,user does not exist!]; arguments []; default message [null]

似乎结果确实有错误，但它的路径是project.id在我的表单中project.manager.id

怎么修？

...
import org.springframework.validation.Validator;
...

@Component
public class ProjectValidator implements Validator {

    @Override
    public boolean supports(Class<?> clazz) {
        return Project.class.equals(clazz);
    }

    @Override
    public void validate(Object target, Errors errors) {
        Project project = (Project) target;

        /* Do your checks here */
        ...

        if (managerIdDoesNotMatch) {
            errors.rejectValue("manager.id", "your_error_code");
        }

        ...

        if (operatorIdDoesNotMatch) {
            errors.rejectValue("operator.id", "your_error_code");
        }

        ...
    }
}

...
public class ProjectController {

    @Autowired
    ProjectValidator projectValidator;

    ...

    @RequestMapping(...)
    public String yourCreateMethod(..., @ModelAttribute @Valid Project project, BindingResult result) {
        projectValidator.validate(project, result);

        if (result.hasErrors()){
          // do something
        }
        else {
          // do something else
        }
    }

}