无法将 java.lang.String 类型的属性值转换为所需的类型实体答案

【问题标题】：Failed to convert property value of type java.lang.String to required type entity无法将 java.lang.String 类型的属性值转换为所需的类型实体
【发布时间】：2020-04-22 18:39:36
【问题描述】：

我是 Spring MVC 的新手，正在尝试构建示例应用程序。我正在尝试将数据保存到表名 EmployeeDetails 中，该表名与表 Users 具有一对一的关系。提交表单后，我收到此错误字段“用户”上的对象“员工详细信息”中的字段错误：拒绝值 [用户]；代码 [typeMismatch.employeeDetails.user,typeMismatch.user,typeMismatch.com.sachinmukherjee.spring_hibernate.entity.Users,typeMismatch];参数 [org.springframework.context.support.DefaultMessageSourceResolvable: 代码 [employeeDetails.user,user];论据 [];默认消息[用户]]；默认消息 [无法将类型“java.lang.String”的属性值转换为属性“用户”所需的类型“com.sachinmukherjee.spring_hibernate.entity.Users”；嵌套异常是 java.lang.IllegalStateException：无法将类型“java.lang.String”的值转换为属性“用户”所需的类型“com.sachinmukherjee.spring_hibernate.entity.Users”：找不到匹配的编辑器或转换策略]]

用户表结构

+--------------+--------------+------+-----+-------------------+----------------+
| Field        | Type         | Null | Key | Default           | Extra          |
+--------------+--------------+------+-----+-------------------+----------------+
| id           | int(11)      | NO   | PRI | NULL              | auto_increment |
| username     | varchar(20)  | NO   | UNI | NULL              |                |
| password     | varchar(100) | NO   |     | NULL              |                |
| created_at   | datetime     | YES  |     | CURRENT_TIMESTAMP |                |
| userfullname | varchar(50)  | NO   |     | NULL              |                |
+--------------+--------------+------+-----+-------------------+----------------+

用户实体(Users.java)

@Entity
@Table(name="users")
public class Users {

    @Id
    @Column(name="id")
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    private int id;

    @Column(name="username",unique = true)
    private String username;

    @Column(name="password")
    private String password;

    @Column(name="userfullname")
    private String userfullname;

    @Column(name = "created_at")
    private Timestamp created_at;

    @OneToOne(mappedBy = "user",
            cascade = CascadeType.PERSIST
            )
    private EmployeeDetails employee;

    public Users() {
    }

    public Users(String username, String password, String userfullname) {
        this.username = username;
        this.password = password;
        this.userfullname = userfullname;
    }

    public String getUsername() {
        return username;
    }

    public void setUsername(String username) {
        this.username = username;
    }

    public Timestamp getCreated_at() {
        return created_at;
    }

    public String getUserfullname() {
        return userfullname;
    }

    public void setUserfullname(String userfullname) {
        this.userfullname = userfullname;
    }

    public void setCreated_at(Timestamp created_at) {
        this.created_at = created_at;
    }

    public int getId() {
        return id;
    }

    public String getPassword() {
        return password;
    }

    public void setPassword(String password) {
        this.password = password;
    }

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

    public EmployeeDetails getEmployee() {
        return employee;
    }

    public void setEmployee(EmployeeDetails employee) {
        this.employee = employee;
    }

    @Override
    public String toString() {
        return "Users [id=" + id + ", username=" + username + ", userfullname=" + userfullname + ", created_at="
                + created_at + "]";
    }
}

EmployeeDetails 表结构

+-------------+-------------+------+-----+-------------------+----------------+
| Field       | Type        | Null | Key | Default           | Extra          |
+-------------+-------------+------+-----+-------------------+----------------+
| id          | int(11)     | NO   | PRI | NULL              | auto_increment |
| first_name  | varchar(20) | NO   |     | NULL              |                |
| middle_name | varchar(20) | YES  |     | NULL              |                |
| last_name   | varchar(20) | YES  |     | NULL              |                |
| mobile_no   | bigint(20)  | YES  |     | NULL              |                |
| email       | varchar(50) | NO   |     | NULL              |                |
| created_at  | datetime    | YES  |     | CURRENT_TIMESTAMP |                |
| users_id    | int(11)     | NO   | MUL | NULL              |                |
+-------------+-------------+------+-----+-------------------+----------------+

EmployeeDetails 实体类(EmployeeDetails.java)

@Entity
@Table(name="employee_details")
public class EmployeeDetails {

    @Id
    @Column(name="id")
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    private int id;

    @Column(name="first_name")
    private String first_name;

    @Column(name="middle_name")
    private String middle_name;

    @Column(name="last_name")
    private String last_name;

    @Column(name="mobile_no")
    private long mobile_no;

    @Column(name="email")
    private String email;

    @OneToOne(fetch = FetchType.EAGER,cascade = CascadeType.PERSIST)
    @JoinColumn(name = "users_id")
    private Users user;

    public EmployeeDetails() {

    }

    public EmployeeDetails(String first_name, String middle_name, String last_name, long mobile_no, String email) {
        this.first_name = first_name;
        this.middle_name = middle_name;
        this.last_name = last_name;
        this.mobile_no = mobile_no;
        this.email = email;
    }

    public int getId() {
        return id;
    }

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

    public String getFirst_name() {
        return first_name;
    }

    public void setFirst_name(String first_name) {
        this.first_name = first_name;
    }

    public String getMiddle_name() {
        return middle_name;
    }

    public void setMiddle_name(String middle_name) {
        this.middle_name = middle_name;
    }

    public String getLast_name() {
        return last_name;
    }

    public void setLast_name(String last_name) {
        this.last_name = last_name;
    }

    public long getMobile_no() {
        return mobile_no;
    }

    public void setMobile_no(long mobile_no) {
        this.mobile_no = mobile_no;
    }

    public String getEmail() {
        return email;
    }

    public void setEmail(String email) {
        this.email = email;
    }

    public Users getUser() {
        return user;
    }

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

    @Override
    public String toString() {
        return "EmployeeDetails [id=" + id + ", first_name=" + first_name + ", middle_name=" + middle_name
                + ", last_name=" + last_name + ", mobile_no=" + mobile_no + ", email=" + email + ", user=" + user + "]";
    }
}

我的 EmployeeDeatails 控制器（EmployeeDetailsController.java）

@Controller
@RequestMapping("/employee_details")
public class EmployeeDetailsController {

    @Autowired
    EmployeeDetailsDAO employeeDetailsDAO;
    @Autowired
    UsersDAO usersDAO;

    @RequestMapping("/")
    public String home(Model model) {
        List<EmployeeDetails> employees = employeeDetailsDAO.getEmployees();
        model.addAttribute("employees", employees);
        return "employee_details/index";
    }

    @GetMapping("/add")
    public String add(Model model) {
        List<Users> users = usersDAO.getUsers();
        EmployeeDetails employee = new EmployeeDetails();
        model.addAttribute("userList",users);
        model.addAttribute("employee", employee);
        return "employee_details/add";
    }

    @PostMapping("/submit")
    public String submit(@ModelAttribute EmployeeDetails employee) {
        System.out.println(employee);
        employeeDetailsDAO.saveEmployee(employee);
        return "redirect:/employee_details/";
    }

}

我的 EmployeeDetails DAO 类（EmployeeDetails DAO）

@Repository
public class EmployeeDetailsDAOImp implements EmployeeDetailsDAO {

    @Autowired
    SessionFactory sessionFactory;

    @Transactional
    public List<EmployeeDetails> getEmployees() {
        Session session = sessionFactory.getCurrentSession();
        Query<EmployeeDetails> query = session.createQuery("from EmployeeDetails",EmployeeDetails.class);
        List<EmployeeDetails> employees = query.getResultList();
        System.out.println(employees);
        return employees;
    }
    @Transactional
    public void saveEmployee(EmployeeDetails employee) {
        Session session = sessionFactory.getCurrentSession();
        session.saveOrUpdate(employee);

    }
}

我用于填写表单的 add.jsp 页面

<form action="${pageContext.request.contextPath}/employee_details/submit" method="POST" modelAttribute="employee" class="form-control">
        <label>Username</label>
        <select name="user" required="required">
             <option>Select User</option>
            <c:forEach var="user" items="${userList}">
                <option value=${user}>${user.username}</option>
            </c:forEach>
        </select>
        <br><br>
        <label>First Name</label>
        <input type="text" name="first_name" />
        <br><br>
        <label>Middle Name</label>
        <input type="text" name="middle_name" />
        <br><br>
        <label>Last Name</label>
        <input type="text" name="last_name" />
        <br><br>
        <label>Email</label>
        <input type="text" name="email" />
        <br><br>
        <button type="submit" class="btn btn-success">Save</button>
    </form>

我的 UsersDao 类

@Repository
public class UsersDAOImp implements UsersDAO {

    //need to inject session factory
    @Autowired
    private SessionFactory sessionFactory;

    @Transactional
    public List<Users> getUsers() {

        //get the hibernate session
        Session session =  sessionFactory.getCurrentSession();
        //create a query 
        Query<Users> theQuery = 
                     session.createQuery("from Users", Users.class);
        //execute the query and get resultset
        List<Users> users = theQuery.getResultList();
        //return the result
        return users;
    }
}

我无法弄清楚为什么会出现此错误以及我应该在提交方法的方法参数中传递什么。

【问题讨论】：

查看生成的HTML的源代码，并查看<option>元素的生成value属性。这对你来说是正确的吗？ --- 该值应该只是一个用户 ID，而不是 Users 对象的 toString() 的结果。这也意味着您不能使用EmployeeDetails 作为submit() 方法的参数。
我已将选项值更改为<option value=${user.id}>${user.username}</option>。我无法弄清楚 submit() 方法的参数应该是什么。
stackoverflow.com/a/3097196/6572971
您将<select name="user"> 更改为<select name="user_id">，并创建一个与EmployeeDetails 类似但没有所有注释的类，其中字段Users user 被int user_id 替换，并在提交方法。然后该方法查找用户并构建一个EmployeeDetails 对象。
所以我目前的申请流程如下。 Controller Class -> Service Class -> DAO Class -> 保存实体。如果我创建一个类似于 EmployeeDetails Entity Class 的新类而没有任何注释，那么我的应用程序的流程应该是什么。

标签： java spring hibernate spring-mvc jsp

【解决方案1】：

我找到的解决方案是将 HTML 表单替换为 spring 表单，并将 select 标记及其路径更改为类似的内容。

<form:label path="user.id">Username</form:label>
        <form:select path="user.id" required="required">
            <form:option value="${user.get(0)}">Select One</form:option>
            <c:forEach var="user" items="${userList}">
                <form:option value="${user.id}">${user.username}</form:option>
            </c:forEach>
</form:select>

【讨论】：