Question

我在此实体中拥有用户实体和字段角色。 角色为ENUM 。我正在尝试从UI创建用户。但是，我得到了一个例外：

org.springframework.beans.NullValueInNestedPathException: Invalid property 'role' of bean class [com.bionic.entities.User]: Could not instantiate property type [com.bionic.entities.Role] to auto-grow nested property path: org.springframework.beans.BeanInstantiationException: Failed to instantiate [com.bionic.entities.Role]: Is it an abstract class?; nested exception is java.lang.InstantiationException: com.bionic.entities.Role

这是我的 Role.Enum ：

package com.bionic.entities;

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

import javax.annotation.Resource;
@Resource
public enum Role {
ADMINISTRATOR(1, "administrator"),
TRAINER(2, "trainer"),
STUDENT(3, "student"),
RESTRICTED_ADMINISTRATOR(4, "restricted_administrator"),
RESTRICTED_TRAINER(5, "restricted_trainer");

private long id;
private String name;


Role(){}

private Role(long id, String name) {
    this.name = name;
    this.id = id;
}

public long getId() {
    return id;
}

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

public String getName() {
    return name;
}

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

}

我的 User.class字段：

public class User {
@Id
@GeneratedValue(strategy = GenerationType.AUTO)
private long id;
@Column(name = "first_name", nullable = false)
private String firstName;
@Column(name = "last_name", nullable = false)
private String lastName;
@Column(name = "email", nullable = false, unique = true)
private String email;
@Column(name = "password", nullable = false)
private String password;
@Column(name = "cell")
private String cell;
@Column(name="position")
private String position;

@Enumerated(EnumType.ORDINAL)
@Column(name = "role_id")
private Role role;

最后，我的 html表单：

<form method="POST" action="/superAdmin/addUser" th:object="${user}">
<select name="role.id" size="2" th:field="*{role.id}" style="display: block" id="role.id"></select>
    <br /> <br /> <input type="submit" value="Upload" class="submit-but">

为了解决这个问题，我花了2天时间。然而，它并不成功

我如何创建实体：

    @RequestMapping(value = "/addUser", method = RequestMethod.POST)
public
@ResponseBody
String addUser(@ModelAttribute User user, Model model) {
    try {
        model.addAttribute("user", user);
        superAdministratorService.addUser(user);
        return "successful";
    } catch (Exception e) {
        return "You failed to upload";
    }
}

Answer 1

Role有一个默认的包级构造函数和一个带有2个参数的私有构造函数，尝试将包级别的构造函数更改为public，以便执行此操作，更改

Role(){}

通过

public Role(){}

我认为这是导致问题的原因。但是你不能在枚举中设置公共构造函数，所以也许你必须将你的实现改为最终的类。

<强>更新

public static Role fromId(long id) {
    if (1 == id) {
        return ADMINISTRATOR;
    }
    // TODO else if for the rest of enum instances
    } else {
        throw new AssertionError("Role not know!"); 
    }
}

可能的解决方案如下：

使用DTO（具有与User实体和getter和setter相同属性的简单POJO）在addUser方法中接收对象，在该DTO中将role定义为整数。
在您的枚举中，创建一个类似上面的方法
使用上述方法从de DTO对象创建实体对象，以在role实体中设置User成员。

提交表单时的Spring枚举异常

1 个答案: