JPA @ManyToMany java.lang.StackOverflowError: null

JPA 懒加载的一个坑 大神可绕路

package com.liuzm.controller;

import com.liuzm.entity.UacRole;
import com.liuzm.entity.UacUser;
import com.liuzm.service.UacUserService;
import org.springframework.web.bind.annotation.GetMapping;
import org.springframework.web.bind.annotation.RestController;

import javax.annotation.Resource;
import java.util.Set;

@RestController
public class UserController {

    @Resource
    private UacUserService uacUserService;

    @GetMapping("/")
    public Set findByLoginName() {
        UacUser uacUser = this.uacUserService.findByLoginName("admin");
        System.out.println(uacUser);
        Set roles = uacUser.getRoles();
        System.out.println(roles.size());
        return roles;
    }
}

---

package com.liuzm.entity;

import com.fasterxml.jackson.annotation.JsonIgnore;

import javax.persistence.*;
import java.io.Serializable;
import java.util.HashSet;
import java.util.Set;

@Entity
@Table(name = "tbl_uac_role")
public class UacRole implements Serializable {
    /**
     * serialVersionUID:用一句话描述这个变量表示什么.
     * @since JDK 1.7
     */
    private static final long serialVersionUID = -6263200210499558891L;

    /**
     * ID
     */
    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    private Long id;

    /**
     * 角色编码
     */
    @Column(name = "role_code")
    private String roleCode;
    @JsonIgnore
    @ManyToMany
    @JoinTable(name = "tbl_uac_role_user", joinColumns = {@JoinColumn(name = "role_id", referencedColumnName = "id")}, inverseJoinColumns = {@JoinColumn(name = "user_id", referencedColumnName = "id")})
    private Set users = new HashSet<>();

    public UacRole() {
    }

    public UacRole(Long id) {
        this.id = id;
    }

    public Long getId() {
        return id;
    }

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

    public String getRoleCode() {
        return roleCode;
    }

    public void setRoleCode(String roleCode) {
        this.roleCode = roleCode;
    }

    public Set getUsers() {
        return users;
    }

    public void setUsers(Set users) {
        this.users = users;
    }

    @Override
    public String toString() {
        return "UacRole{" +
                "id=" + id +
                ", roleCode='" + roleCode + '\'' +
                ", users=" + users +
                '}';
    }
}

package com.liuzm.entity;

import com.fasterxml.jackson.annotation.JsonIgnore;

import javax.persistence.*;
import java.io.Serializable;
import java.util.HashSet;
import java.util.Set;

@Entity
@Table(name = "tbl_uac_user")
public class UacUser implements Serializable {
    /**
     * serialVersionUID:用一句话描述这个变量表示什么.
     * @since JDK 1.7
     */
    private static final long serialVersionUID = 3439493474130693948L;

    /**
     * ID
     */
    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    private Long id;

    /**
     * 登录名
     */
    @Column(name = "login_name")
    private String loginName;
    @ManyToMany(mappedBy = "users")
    @JsonIgnore
    private Set roles = new HashSet<>();

    @Override
    public String toString() {
        return "UacUser{" +
                "id='" + id + '\'' +
                ", loginName='" + loginName + '\'' +
                ", roles=" + roles +
                '}';
    }



    public UacUser() {
    }
    public UacUser(Long id) {
        this.id = id;
    }


    public Long getId() {
        return id;
    }

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

    public String getLoginName() {
        return loginName;
    }

    public void setLoginName(String loginName) {
        this.loginName = loginName;
    }

    public Set getRoles() {
        return roles;
    }

    public void setRoles(Set roles) {
        this.roles = roles;
    }
}

---

package com.liuzm.repository;

import com.liuzm.entity.UacUser;
import org.springframework.data.jpa.repository.JpaRepository;


public interface UacUserRepository extends JpaRepository<UacUser, Long> {

    UacUser findByLoginName(String loginName);
}

---

package com.liuzm.service;

import com.liuzm.entity.UacUser;

public interface UacUserService {

    UacUser findByLoginName(String loginName);
}

---

server:
  port: 8000
  tomcat:
    uri-encoding: UTF-8
spring:
  application:
    name: jpa-test
  jpa:
      generate-ddl: false
      show-sql: true
      hibernate:
        ddl-auto: update
      properties:
        hibernate:
          dialect: org.hibernate.dialect.MySQL5Dialect
  datasource:
    driver-class-name: com.mysql.jdbc.Driver
    url: jdbc:mysql://localhost/test?useUnicode=true&characterEncoding=UTF-8
    username: root
    password: 123456
logging:
  level:
    root: INFO
    org.hibernate: INFO
    org.hibernate.type.descriptor.sql.BasicBinder: TRACE
    org.hibernate.type.descriptor.sql.BasicExtractor: TRACE

错误如下

Hibernate: select uacuser0_.id as id1_2_, uacuser0_.login_name as login_na2_2_ from tbl_uac_user uacuser0_ where uacuser0_.login_name=?
2017-04-19 13:49:46.187 TRACE 14504 --- [nio-8000-exec-1] o.h.type.descriptor.sql.BasicBinder      : binding parameter [1] as [VARCHAR] - [admin]
2017-04-19 13:49:46.191 TRACE 14504 --- [nio-8000-exec-1] o.h.type.descriptor.sql.BasicExtractor   : extracted value ([id1_2_] : [BIGINT]) - [222]
2017-04-19 13:49:46.195 TRACE 14504 --- [nio-8000-exec-1] o.h.type.descriptor.sql.BasicExtractor   : extracted value ([login_na2_2_] : [VARCHAR]) - [admin]
Hibernate: select roles0_.user_id as user_id2_1_0_, roles0_.role_id as role_id1_1_0_, uacrole1_.id as id1_0_1_, uacrole1_.role_code as role_cod2_0_1_ from tbl_uac_role_user roles0_ inner join tbl_uac_role uacrole1_ on roles0_.role_id=uacrole1_.id where roles0_.user_id=?
2017-04-19 13:49:46.208 TRACE 14504 --- [nio-8000-exec-1] o.h.type.descriptor.sql.BasicBinder      : binding parameter [1] as [BIGINT] - [222]
2017-04-19 13:49:46.213 TRACE 14504 --- [nio-8000-exec-1] o.h.type.descriptor.sql.BasicExtractor   : extracted value ([id1_0_1_] : [BIGINT]) - [1234]
2017-04-19 13:49:46.213 TRACE 14504 --- [nio-8000-exec-1] o.h.type.descriptor.sql.BasicExtractor   : extracted value ([role_cod2_0_1_] : [VARCHAR]) - [admin]
2017-04-19 13:49:46.214 TRACE 14504 --- [nio-8000-exec-1] o.h.type.descriptor.sql.BasicExtractor   : extracted value ([user_id2_1_0_] : [BIGINT]) - [222]
2017-04-19 13:49:46.214 TRACE 14504 --- [nio-8000-exec-1] o.h.type.descriptor.sql.BasicExtractor   : extracted value ([role_id1_1_0_] : [BIGINT]) - [1234]
Hibernate: select users0_.role_id as role_id1_1_0_, users0_.user_id as user_id2_1_0_, uacuser1_.id as id1_2_1_, uacuser1_.login_name as login_na2_2_1_ from tbl_uac_role_user users0_ inner join tbl_uac_user uacuser1_ on users0_.user_id=uacuser1_.id where users0_.role_id=?
2017-04-19 13:49:46.217 TRACE 14504 --- [nio-8000-exec-1] o.h.type.descriptor.sql.BasicBinder      : binding parameter [1] as [BIGINT] - [1234]
2017-04-19 13:49:46.218 TRACE 14504 --- [nio-8000-exec-1] o.h.type.descriptor.sql.BasicExtractor   : extracted value ([id1_2_1_] : [BIGINT]) - [222]
2017-04-19 13:49:46.218 TRACE 14504 --- [nio-8000-exec-1] o.h.type.descriptor.sql.BasicExtractor   : extracted value ([role_id1_1_0_] : [BIGINT]) - [1234]
2017-04-19 13:49:46.218 TRACE 14504 --- [nio-8000-exec-1] o.h.type.descriptor.sql.BasicExtractor   : extracted value ([user_id2_1_0_] : [BIGINT]) - [222]
2017-04-19 13:49:46.271 ERROR 14504 --- [nio-8000-exec-1] o.a.c.c.C.[.[.[/].[dispatcherServlet]    : Servlet.service() for servlet [dispatcherServlet] in context with path [] threw exception [Handler dispatch failed; nested exception is java.lang.StackOverflowError] with root cause

java.lang.StackOverflowError: null
    at java.util.AbstractCollection.toString(AbstractCollection.java:454) ~[na:1.8.0_60]
    at org.hibernate.collection.internal.PersistentSet.toString(PersistentSet.java:300) ~[hibernate-core-5.0.12.Final.jar:5.0.12.Final]
    at java.lang.String.valueOf(String.java:2994) ~[na:1.8.0_60]
    at java.lang.StringBuilder.append(StringBuilder.java:131) ~[na:1.8.0_60]
    at com.liuzm.entity.UacUser.toString(UacUser.java:37) ~[classes/:na]
    at java.lang.String.valueOf(String.java:2994) ~[na:1.8.0_60]
    at java.lang.StringBuilder.append(StringBuilder.java:131) ~[na:1.8.0_60]
    at java.util.AbstractCollection.toString(AbstractCollection.java:462) ~[na:1.8.0_60]
    at org.hibernate.collection.internal.PersistentSet.toString(PersistentSet.java:300) ~[hibernate-core-5.0.12.Final.jar:5.0.12.Final]
    at java.lang.String.valueOf(String.java:2994) ~[na:1.8.0_60]
    at java.lang.StringBuilder.append(StringBuilder.java:131) ~[na:1.8.0_60]
    at com.liuzm.entity.UacRole.toString(UacRole.java:69) ~[classes/:na]
    at java.lang.String.valueOf(String.java:2994) ~[na:1.8.0_60]
    at java.lang.StringBuilder.append(StringBuilder.java:131) ~[na:1.8.0_60]
    at java.util.AbstractCollection.toString(AbstractCollection.java:462) ~[na:1.8.0_60]
    at org.hibernate.collection.internal.PersistentSet.toString(PersistentSet.java:300) ~[hibernate-core-5.0.12.Final.jar:5.0.12.Final]
    at java.lang.String.valueOf(String.java:2994) ~[na:1.8.0_60]
    at java.lang.StringBuilder.append(StringBuilder.java:131) ~[na:1.8.0_60]
    at com.liuzm.entity.UacUser.toString(UacUser.java:37) ~[classes/:na]
    at java.lang.String.valueOf(String.java:2994) ~[na:1.8.0_60]
    at java.lang.StringBuilder.append(StringBuilder.java:131) ~[na:1.8.0_60]
    at java.util.AbstractCollection.toString(AbstractCollection.java:462) ~[na:1.8.0_60]
    at org.hibernate.collection.internal.PersistentSet.toString(PersistentSet.java:300) ~[hibernate-core-5.0.12.Final.jar:5.0.12.Final]
    at java.lang.String.valueOf(String.java:2994) ~[na:1.8.0_60]
    at java.lang.StringBuilder.append(StringBuilder.java:131) ~[na:1.8.0_60]
    at com.liuzm.entity.UacRole.toString(UacRole.java:69) ~[classes/:na]
    at java.lang.String.valueOf(String.java:2994) ~[na:1.8.0_60]
    at java.lang.StringBuilder.append(StringBuilder.java:131) ~[na:1.8.0_60]
    at java.util.AbstractCollection.toString(AbstractCollection.java:462) ~[na:1.8.0_60]
    at org.hibernate.collection.internal.PersistentSet.toString(PersistentSet.java:300) ~[hibernate-core-5.0.12.Final.jar:5.0.12.Final]
    at java.lang.String.valueOf(String.java:2994) ~[na:1.8.0_60]
    at java.lang.StringBuilder.append(StringBuilder.java:131) ~[na:1.8.0_60]
    at com.liuzm.entity.UacUser.toString(UacUser.java:37) ~[classes/:na]
    at java.lang.String.valueOf(String.java:2994) ~[na:1.8.0_60]
    at java.lang.StringBuilder.append(StringBuilder.java:131) ~[na:1.8.0_60]
    at java.util.AbstractCollection.toString(AbstractCollection.java:462) ~[na:1.8.0_60]
    at org.hibernate.collection.internal.PersistentSet.toString(PersistentSet.java:300) ~[hibernate-core-5.0.12.Final.jar:5.0.12.Final]
    at java.lang.String.valueOf(String.java:2994) ~[na:1.8.0_60]
    at java.lang.StringBuilder.append(StringBuilder.java:131) ~[na:1.8.0_60]
    at com.liuzm.entity.UacRole.toString(UacRole.java:69) ~[classes/:na]
    at java.lang.String.valueOf(String.java:2994) ~[na:1.8.0_60]
    at java.lang.StringBuilder.append(StringBuilder.java:131) ~[na:1.8.0_60]
    at java.util.AbstractCollection.toString(AbstractCollection.java:462) ~[na:1.8.0_60]
    at org.hibernate.collection.internal.PersistentSet.toString(PersistentSet.java:300) ~[hibernate-core-5.0.12.Final.jar:5.0.12.Final]
    at java.lang.String.valueOf(String.java:2994) ~[na:1.8.0_60]
    at java.lang.StringBuilder.append(StringBuilder.java:131) ~[na:1.8.0_60]
    at com.liuzm.entity.UacUser.toString(UacUser.java:37) ~[classes/:na]
    at java.lang.String.valueOf(String.java:2994) ~[na:1.8.0_60]
    at java.lang.StringBuilder.append(StringBuilder.java:131) ~[na:1.8.0_60]
    at java.util.AbstractCollection.toString(AbstractCollection.java:462) ~[na:1.8.0_60]
    at org.hibernate.collection.internal.PersistentSet.toString(PersistentSet.java:300) ~[hibernate-core-5.0.12.Final.jar:5.0.12.Final]
    at java.lang.String.valueOf(String.java:2994) ~[na:1.8.0_60]
    at java.lang.StringBuilder.append(StringBuilder.java:131) ~[na:1.8.0_60]
    at com.liuzm.entity.UacRole.toString(UacRole.java:69) ~[classes/:na]
    at java.lang.String.valueOf(String.java:2994) ~[na:1.8.0_60]
    at java.lang.StringBuilder.append(StringBuilder.java:131) ~[na:1.8.0_60]
    at java.util.AbstractCollection.toString(AbstractCollection.java:462) ~[na:1.8.0_60]
    at org.hibernate.collection.internal.PersistentSet.toString(PersistentSet.java:300) ~[hibernate-core-5.0.12.Final.jar:5.0.12.Final]
    at java.lang.String.valueOf(String.java:2994) ~[na:1.8.0_60]

在网上查了一下,和大神们的问题略有不同,这里具体原因是 两个类都有toString(), 而两个类中同时使用了懒加载(默认)这样在A类toString的时候会发sql查询B类,而B类toString()又会发sql查A类这样会发生死循环最后导致java.lang.StackOverflowError.初用JPA 出现问题引以为鉴.

完整代码

最后做一下说明 如果是springmvc jackson报response错误 那么最好是 多对多维护关系都不要toString() Set集合对象, 然后使用 dto 或者 vo 去做数据的传输去解决这个问题. 具体原因有待日后解决