Spring MVC - 將屬性設置爲控制器中的@ModelAttribute對象

Question

我開始使用Spring，並且發現了一個我無法理清的問題。 我有一個用戶的實體，具有「角色」屬性，「角色」是一個集合對象，該estity如下：

private String id; 
private String name; 
private String surname; 
private String email; 
private String identificationNumber; 
private String username; 
private String password; 
private String passwordConfirm; 
private int sex; 
private Timestamp birthDate; 
private Set<Role> roles; 

@Id 
@GeneratedValue(generator = "uuid") 
@GenericGenerator(name = "uuid", strategy = "uuid2") 
public String getId() { 
    return id; 
} 

public void setId(String id) { 
    this.id = id; 
} 

@ManyToMany(fetch = FetchType.EAGER) 
@JoinTable(name = "user_role", joinColumns = @JoinColumn(name = "user_id"), inverseJoinColumns = @JoinColumn(name = "role_id")) 
public Set<Role> getRoles() { 
    return roles; 
} 

public void setRoles(Set<Role> roles) { 
    this.roles = roles; 
} 

我的「角色」實體如下：

private String id; 
private String name; 
private Set<User> users; 

@Id 
@GeneratedValue(generator = "uuid") 
@GenericGenerator(name = "uuid", strategy = "uuid2") 
public String getId() { 
    return id; 
} 

public void setId(String id) { 
    this.id = id; 
} 

public String getName() { 
    return name; 
} 

public void setName(String name) { 
    this.name = name; 
} 

@ManyToMany(mappedBy = "roles") 
public Set<User> getUsers() { 
    return users; 
} 

public void setUsers(Set<User> users) { 
    this.users = users; 
} 

在JSP中我有一個列表中選擇一個組合框的所有「角色」

<spring:bind path="roles"> 
    <div class="input-field is-empty cell2"> 
     <form:select type="text" path="roles" class="validate ${status.error ? 'invalid' : ''}"> 
       <form:option value="NONE" selected="selected" disabled="true">Roles</form:option> 
       <c:forEach items="${allRoles}" var="role"> 
       <form:option value="${role.getId()}" >${role.getName() }</form:option> 
       </c:forEach> 
      </form:select> 
      <form:errors path="roles" class="alert alert-dismissible alert-danger"> </form:errors> 
     <span class="material-input"></span> 
    </div> 
</spring:bind> 

我選擇一個或多個「角色」，並提交形式如下控制器，在此存在@RequestParam與ID列表所選'角色'

@RequestMapping(value="/user_edit/{id}", method=RequestMethod.POST) 
public String edit_user(@ModelAttribute("userForm") User userForm, BindingResult bindingResult, @PathVariable String id, @RequestParam String role_ids) { 
    Set<Role> role_list = new HashSet<Role>(); 
    for (String role_id : role_ids.split(",")) { 
     Role _role = roleService.getById(role_id); 
     Role role = new Role(); 
     role.setName(_role.getName()); 
     role.setId(role_id); 
     role_list.add(role); 
    } 
    userForm.setRoles(role_list); 
    userValidator.validate(userForm, bindingResult, false); 
    if (bindingResult.hasErrors()) { 
     return "edit_user"; 
    } 
    userService.save(userForm); 
    return "redirect:/users"; 
} 

在userValidator.validate（userForm，bindingResult，false）;該程序會顯示以下錯誤：

Failed to convert property value of type [java.lang.String[]] to required type [java.util.Set] for property roles; nested exception is java.lang.IllegalStateException: Cannot convert value of type [java.lang.String] to required type [com.gestcart.account.model.Role] for property roles[0]: no matching editors or conversion strategy found 

請幫助解決這個問題

Answer 1

你必須創建在用戶實體的String [] rolesSelect或列表<字符串> rolesSelect一個新的領域。如果你想跳過它，因爲它是一個實體類。然後你就可以從你的modelattribute「user」訪問它，你不需要單獨的請求參數，即'< spring：bind path =「roles」>'是不需要的。 在您的jsp上使用以下代碼：

<form:select type="text" path="rolesSelect" class="validate ${status.error ? 'invalid' : ''}"> 
      <form:option value="NONE" selected="selected" disabled="true">Roles</form:option> 
      <c:forEach items="${allRoles}" var="role"> 
      <form:option value="${role.getId()}" >${role.getName() }</form:option> 
      </c:forEach> 
     </form:select>