我对spring和java比较新，正在使用jsp、jstl、hibernate/jpa和一个模型类让表单在springmvc中工作。我可以让页面显示得很好，但是应该创建用户的帖子给了我一个错误。

Failed to convert property value of type java.lang.String to required type com.everesttech.recruiting.searchtool.entity.Role for property user.role; nested exception is java.lang.IllegalStateException: Cannot convert value of type [java.lang.String] to required type [com.everesttech.recruiting.searchtool.entity.Role] for property role: no matching editors or conversion strategy found

此错误是有意义的，因为窗体正在传回角色的id，而用户对象希望传递角色对象。但是，我不知道如何解决这个问题，同时仍然允许我的jsp由实际的实体对象支持，因为我想使用spring/hibernate验证。有没有一种方法可以证明这一点form:select as 角色对象？任何建议或解决方案都将不胜感激。提前谢谢。
我已经从我的项目中提供了代码的相关部分。我没有包含来自服务层和实体层的代码，因为我知道它们正在工作。不过，我可以包括这些以及如果需要。用户与角色具有多对一关系。
用户控制器

/**
 * display the user add page
 * 
 * @return              returns the view name
 */
@RequestMapping(value="/user/add", method=RequestMethod.GET)
public ModelAndView showUserAdd(ServletRequest request, @ModelAttribute("userModel") UserModel userModel, ModelMap modelmap) {  

    ModelMap modelMap = new ModelMap();
    userModel.setUser(new User());
    userModel.setRoles(userService.getRoles());
    modelMap.addAttribute("userModel", userModel);

    return new ModelAndView("user/add", modelMap);
}

/**
 * handle post request to handle user creation, if successful displays user list page
 * 
 * @param user          User object from JSP
 * @param result        BindingResult from JSP
 * @return              returns view name
 */
@RequestMapping(value="/user/add", method=RequestMethod.POST)
public String userAdd(UserModel userModel, BindingResult result) {

    if (result.hasErrors()) {
        logger.warn("Error binding UserModel for /user/add, returning to previous page");
        List<ObjectError> errors = result.getAllErrors();
        for (ObjectError error : errors) {
            logger.warn(error.getCode() + " - " + error.getDefaultMessage());
        }
        return "user/add";
    }

    try {
        User user = userModel.getUser();
        userService.addUser(user);
    }
    catch (DuplicateKeyException e) {
        logger.warn("Duplicate record found in User table", e);
    }
    catch (Exception e) {
        logger.error("Error occurred while trying to create a new user", e);
    }

    return "/user";
}

这是我传递给jsp的模型，jsp包含一个用户对象（hibernate实体）和一个角色列表（另一个hibernate实体）。

import java.util.List;

import org.springframework.context.annotation.Scope;
import org.springframework.stereotype.Component;

import com.everesttech.recruiting.searchtool.entity.Role;
import com.everesttech.recruiting.searchtool.entity.User;

@Scope(value="request")
@Component("userModel")
public class UserModel {

    public User user;
    public List<Role> roles;

    public UserModel() {

    }

    public UserModel(User user, List<Role> roles) {
        this.user = user;
        this.roles = roles;
    }

    public User getUser() {
        return user;
    }

    public void setUser(User user) {
        this.user = user;
    }

    public List<Role> getRoles() {
        return roles;
    }

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

    @Override
    public String toString() {
        return "UserModel [user=" + user + ", roles=" + roles + "]";
    }
}

这是我的jsp。

<%@ taglib uri="http://java.sun.com/jsp/jstl/core" prefix="c" %>
<%@ taglib prefix="sf" uri="http://www.springframework.org/tags/form" %>
<%@ taglib prefix="spring" uri="http://www.springframework.org/tags" %>

<div class="container">
    <div class="row">
        <div class="col-xs-12 col-sm-8 col-md-6">
            <h3>User - Add</h3>
            <br>

            <spring:hasBindErrors name="userModel">
                <div class="alert alert-danger">
                    <sf:errors path="userModel.user.firstName"></sf:errors>
                    <sf:errors path="userModel.user.lastName"></sf:errors>
                    <sf:errors path="userModel.user.email"></sf:errors>
                    <sf:errors path="userModel.user.userName"></sf:errors>
                    <sf:errors path="userModel.user.password"></sf:errors>
                    <sf:errors path="userModel.user.role"></sf:errors>
                </div>
            </spring:hasBindErrors>

            <c:url var="formAction" value="/user/add" />

            <sf:form commandName="userModel" modelAttribute="userModel" method="post" action="${formAction}"> 
                <div class="form-group">
                    <label for="first-name">First Name</label>
                    <sf:input path="user.firstName" id="first-name" class="form-control" placeholder="First Name" />
                </div>
                <div class="form-group">
                    <label for="last-name">Last Name</label>
                    <sf:input path="user.lastName" id="last-name" class="form-control" placeholder="Last Name" />
                </div>
                <div class="form-group">
                    <label for="email">Email</label>
                    <sf:input path="user.email" id="email" class="form-control" placeholder="Email" />
                </div>
                <div class="form-group">
                    <label for="user-name">Username</label>
                    <sf:input path="user.userName" id="user-name" class="form-control" placeholder="Username" />
                </div>
                <div class="form-group">
                    <label for="password">Password</label>
                    <sf:password path="user.password" id="password" class="form-control" placeholder="" />
                </div>
                <div class="form-group">
                    <label for="confirm-password">Confirm Password</label>
                    <input type="password" id="confirm-password" class="form-control" placeholder="" />
                </div>
                <div class="form-group">
                    <label for="role">Role</label>
                    <sf:select path="user.role" id="role" class="form-control" >
                        <c:forEach var="r" items="${userModel.roles}">
                            <sf:option value="${r.getId()}">${r.getFriendlyName()}</sf:option>
                        </c:forEach>
                    </sf:select>
                </div>
                <button type="submit" class="btn btn-default">Save</button>
                <button type="button" class="btn btn-default">Cancel</button>
            </sf:form>
        </div>
    </div>
</div>