Spring MVC @ModelAttribute 方法返回“错误请求”400

Question

美好的一天。我遇到了一个问题：我正在尝试发送带有某些属性的 POST 请求，但我收到“错误请求”响应。

这是我的控制器：

@Controller
@RequestMapping("/group")
public class GroupController {

   private static org.apache.log4j.Logger logger = org.apache.log4j.Logger
     .getLogger(GroupController.class);

   @Autowired
   private GroupService                   groupService;

   @RequestMapping(value = "/add", method = RequestMethod.POST)
   public String addGroup(@ModelAttribute("group") final Group group) {

      GroupController.logger.info("I'm in POST method");
      this.groupService.addGroup(group);
      return "redirect:/student/add";
   }
}

这是我的实体：

@Entity
@Table(name = "university_groups")
public class Group implements Serializable {

   private static final long serialVersionUID = 1L;

   @OneToMany(fetch = FetchType.EAGER, cascade = CascadeType.ALL, mappedBy = "group")
   Set<Student>              students;

   @ManyToOne(fetch = FetchType.EAGER, cascade = CascadeType.ALL)
   @NotNull
   @JoinColumn(name = "department_id")
   private Department        department;

   @Id
   @Column(name = "group_name", unique = true, nullable = false)
   private String            group;

   public Group() {

   }

   public Group(final String group, final Department deparment) {

      this.group = group;
      this.department = deparment;
   }

   public Department getDepartment() {

      return this.department;
   }

   public String getGroup() {

      return this.group;
   }

   public Set<Student> getStudents() {

      return this.students;
   }

   public void setDepartment(final Department department) {

      this.department = department;
   }

   public void setGroup(final String group) {

      this.group = group;
   }

   public void setStudents(final Set<Student> students) {

      this.students = students;
   }

   @Override
   public String toString() {

      return this.group;
   }

}

这是JSP页面的一部分：

<form:form method="POST" action="add" commandName="group">
    <table>
        <tr>
            <td><form:label path="group">
                    <spring:message code="label.student.group" />
                </form:label></td>
            <td><form:input path="group" /></td>
        </tr>
        <tr>
            <td><form:label path="department">
                    <spring:message code="label.student.department" />
                </form:label></td>
            <td><form:select path="department">
                    <form:options items="${departments}" />
                </form:select></td>
            <td><a href="<c:url value="/department/add"/>"><spring:message
                        code="label.student.addDepartment" /></a></td>
        </tr>
        <tr>
            <td colspan="2"><input type="submit"
                value="<spring:message code="label.student.addGroup"/>" /></td>
        </tr>
    </table>
</form:form>

这是部门实体：

@Entity
@Table(name = "departments")
public class Department implements Serializable {

   private static final long serialVersionUID = 1L;

   @Id
   @Column(name = "department", unique = true, nullable = false)
   private String            department;

   @ManyToOne(fetch = FetchType.EAGER, cascade = CascadeType.ALL)
   @NotNull
   @JoinColumn(name = "faculty_id")
   private Faculty           faculty;

   @OneToMany(fetch = FetchType.EAGER, cascade = CascadeType.ALL, mappedBy = "department")
   private Set<Group>        groups;

   @ManyToMany(fetch = FetchType.LAZY)
   @JoinTable(name = "users_departments", joinColumns = {@JoinColumn(name = "department_id", nullable = false, insertable = true, updatable = true) }, inverseJoinColumns = {@JoinColumn(name = "user_name", nullable = false, insertable = true, updatable = true) })
   private Set<User>         users;

   public Department() {

   }

   public Department(final String department, final Faculty faculty) {

      this.department = department;
      this.faculty = faculty;
   }

   public String getDepartment() {

      return this.department;
   }

   public Faculty getFaculty() {

      return this.faculty;
   }

   public Set<Group> getGroups() {

      return this.groups;
   }

   public Set<User> getUsers() {

      return this.users;
   }

   public void setDepartment(final String department) {

      this.department = department;
   }

   public void setFaculty(final Faculty faculty) {

      this.faculty = faculty;
   }

   public void setGroups(final Set<Group> groups) {

      this.groups = groups;
   }

   public void setUsers(final Set<User> users) {

      this.users = users;
   }

   @Override
   public String toString() {

      return this.department;
   }

}

如果我从控制器方法中删除 @ModelAttribute("group") final Group 组，一切正常。 请帮帮我，我不明白为什么它不起作用。

Answer 1

除了 Juergen Hoeller，没有人完全理解 @ModelAttribute。好像他们创造它是为了吓跑新人。

他们真的需要把名字改成@ReadModelAttribute。

你不需要@ModelAttribute参数注解仅仅使用POJO作为参数。

您仅出于以下原因之一需要它：

1. 阅读flashAttribute
2. 阅读@SessionAttribute
3. 读取@ModelAttribute method（应重命名为@WriteModelAttribute）

由于您没有执行任何这些操作，因此请不要在此处使用@ModelAttribute 参数注释。