使用休眠模式訪問數據時發生java.lang.StackOverflowError

Question

當我嘗試在休眠狀態下加入2個表時出現錯誤。 復制的代碼在這里。

/*ADDRESS table entity mapping */

@Entity
@Table(name = "ADDRESS")
public class AddressEntity {

    @ManyToOne(fetch = FetchType.EAGER, cascade = { CascadeType.ALL })
    @JoinColumn(name = "user_id")
    private UserEntity user;

    // setters and getters and other attributes.

}


/* APPUSER table entity mapping */

@Entity
@Table(name = "APPUSER")
public class UserEntity {

    @Id
    @GeneratedValue
    @Column(name = "USER_ID")
    private Long userId;

    @OneToMany(fetch = FetchType.EAGER, mappedBy = "user")
    private Set<AddressEntity> addresses;

    // setters and getters and other attributes.

}

問題在於地址和用戶實體的映射。 每個用戶可以有多個地址，這是必需的。 請幫忙。

下面是復制表DDL語句。它是用戶和地址表之間的一對多關系。

SQL表：

CREATE TABLE `appuser` (
    `user_id` int(11) NOT NULL AUTO_INCREMENT,
    `first_name` varchar(255) NOT NULL,
    `last_name` varchar(255) DEFAULT NULL,
    `email_address` varchar(1024) NOT NULL,
    `password` varchar(1024) NOT NULL,
    `active` tinyint(1) DEFAULT '1',
    `popularity_rating` int(11) DEFAULT NULL,
    `join_date` timestamp NOT NULL DEFAULT CURRENT_TIMESTAMP,
    PRIMARY KEY (`user_id`)
) ENGINE=InnoDB AUTO_INCREMENT=7 DEFAULT CHARSET=utf8

CREATE TABLE `address` (
    `address_id` int(11) NOT NULL AUTO_INCREMENT,
    `address_line1` varchar(38) NOT NULL,
    `address_line2` varchar(38) NOT NULL,
    `city` varchar(38) NOT NULL,
    `state` varchar(38) NOT NULL,
    `zip` varchar(10) NOT NULL,
    `address_type` varchar(45) NOT NULL,
    `user_id` int(11) NOT NULL,
    PRIMARY KEY (`address_id`),
    KEY `fk_address_user_idx` (`user_id`),
    CONSTRAINT `fk_address_user` FOREIGN KEY (`user_id`) REFERENCES `appuser` (`user_id`)
) ENGINE=InnoDB AUTO_INCREMENT=9 DEFAULT CHARSET=utf8

上面連接ADDRESS和USER表給了我StackOverflowError。

預期結果是：

{
    "userId": 1,
    "firstName": "alb",
    "lastName": "va",
    "emailAddress": "alb@va.com",
    "password": "albva",
    "addresses": [
        {
            "addressLine1": "222 plano pkwy",
            "addressLine2": "apt 22",
            "city": "plano",
            "state": "tx",
            "zip": "75034",
            "country": null
        }, {
            "addressLine1": "555 plano pkwy",
            "addressLine2": "apt 11",
            "city": "plano",
            "state": "tx",
            "zip": "75024",
            "country": null
        }
    ],
    "popularityRating": 6,
    "joinDate": 1504897922000,
    "roles": []
}

結果我在調用Web服務時遇到一個無限循環。這是導致堆棧溢出錯誤的原因：

{"userId":2,"firstName":"rax","lastName":"tax","emailAddress":"rax@tax.com","password":"raxtax","addresses":[{"addressLine1":"2001 spring creek","addressLine2":"apt 724","city":"plano","state":"tx","zip":"75074","country":null,"addressType":null,"user":{"userId":2,"firstName":"rax","lastName":"tax","emailAddress":"rax@tax.com","password":"raxtax","addresses":[{"addressLine1":"2001 spring creek","addressLine2":"apt 724","city":"plano","state":"tx","zip":"75074","country":null,"addressType":null,"user":{"userId":2,"firstName":"rax","lastName":"tax","emailAddress":"rax@tax.com","password":"raxtax","addresses":[{"addressLine1":"2001 spring creek","addressLine2":"apt 724","city":"plano","state":"tx","zip":"75074","country":null,"addressType":null,"user":{"userId":2,"firstName":"rax","lastName":"tax","emailAddress":"rax@tax.com","password":"raxtax","addresses":[{"addressLine1":"2001 spring creek","addressLine2":"apt 724","city":"plano","state":"tx","zip":"75074","country":null,"addressType":null,"user":{"userId":2,"firstName":"rax","lastName":"tax","emailAddress":"rax@tax.com","password":"raxtax","addresses":[{"addressLine1":"2001 spring creek","addressLine2":"apt 724","city":"plano","state":"tx","zip":"75074","country":null,"addressType":null,"user":{"userId":2,"firstName":"rax","lastName":"tax","emailAddress":"rax@tax.com","password":"raxtax","addresses":[{"addressLine1":"2001 spring creek","addressLine2":"apt 724","city":"plano","state":"tx","zip":"75074","country":null,"addressType":null,"user":{"userId":2,"firstName":"rax","lastName":"tax","emailAddress":"rax@tax.com","password":"raxtax","addresses":[{"addressLine1":"2001 spring creek","addressLine2":"apt 724","city":"plano","state":"tx","zip":"75074","country":null,"addressType":null,"user": ...

Answer 1

如前所述，當您試圖連接兩個相互依賴的表時，必然會發生無限循環，因為表A試圖從表B中獲取數據。表B依賴於表A並嘗試從中獲取數據。表A.它遇到無限循環，並因此繼續引起堆棧溢出異常。 解決方案是用@JsonManagedReference和@JsonBackReference注釋字段。 這樣，標有@JsonManagedReference的類將被序列化，而標有@JsonBackReference的類則不會被序列化。 這打破了無限循環。 在您的代碼中，您的實體將如下所示；

/*ADDRESS table entity mapping */

@Entity
@Table(name = "ADDRESS")
public class AddressEntity {

@ManyToOne(fetch = FetchType.EAGER, cascade = { CascadeType.ALL })
@JoinColumn(name = "user_id")
@JsonBackReference
private UserEntity user;

// setters and getters and other attributes.

}


/* APPUSER table entity mapping */

@Entity
@Table(name = "APPUSER")
public class UserEntity {

@Id
@GeneratedValue
@Column(name = "USER_ID")
private Long userId;

@OneToMany(fetch = FetchType.EAGER, mappedBy = "user")
@JsonManagedReference
private Set<AddressEntity> addresses;

// setters and getters and other attributes.

}