Spring MVC - 将属性设置为控制器中的@ModelAttribute对象

Question

我开始使用Spring，并且发现了一个我无法理清的问题。 我有一个用户的实体，具有“角色”属性，“角色”是一个集合对象，该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”实体如下：

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中我有一个列表中选择一个组合框的所有“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> 

我选择一个或多个“角色”，并提交形式如下控制器，在此存在@RequestParam与ID列表所选'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）;该程序会显示以下错误：

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 

请帮助解决这个问题

Answer 1

你必须创建在用户实体的String [] rolesSelect或列表<字符串> rolesSelect一个新的领域。如果你想跳过它，因为它是一个实体类。然后你就可以从你的modelattribute“user”访问它，你不需要单独的请求参数，即'< spring：bind path =“roles”>'是不需要的。 在您的jsp上使用以下代码：

<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>