Spring MVC @ModelAttribute方法返回「錯誤請求」400

Question

美好的一天。我遇到了一個問題：我試圖發送帶有一些屬性的POST請求，但是我收到了「錯誤的請求」響應。

這裏是我的控制器：

@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"; 
    } 
} 

這裏是我的實體：

@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; 
    } 

} 

這裏是JSP頁面的一部分：

<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> 

這裏是Department實體：

@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; 
    } 

} 

如果我從控制器方法中刪除@ModelAttribute（「group」）最後一個Group Group，一切正常。 請幫助我，我不明白爲什麼它不起作用。

Answer 1

除了Juergen Hoeller以外，沒有人完全理解@ModelAttribute。就好像他們創造了它來嚇跑新人。

他們確實需要將名稱更改爲@ReadModelAttribute。

您不需要@ModelAttribute參數註釋只是爲了使用POJO作爲參數。

你只需要它的原因如下：

1. 閱讀flashAttribute
2. 閱讀@SessionAttribute
3. 閱讀@ModelAttribute method（應改名爲@WriteModelAttribute）

由於您沒有執行任何這些操作，因此請勿在此處使用@ModelAttribute參數註釋。