hibernate无限递归问题

时间：2023-03-08 21:59:00

项目异常如下：

2018-01-26 17:12:38.162  WARN 3128 --- [nio-8080-exec-6] .w.s.m.s.DefaultHandlerExceptionResolver : Failed to write HTTP message: org.springframework.http.converter.HttpMessageNotWritableException: Could not write JSON: Infinite recursion (*Error); nested exception is com.fasterxml.jackson.databind.JsonMappingException: Infinite recursion (*Error) (through reference chain: demo.server.core.domain.User["userAddresses"]->

org.hibernate.collection.internal.PersistentBag[0]->

demo.server.core.domain.UserAddress["user"]->

demo.server.core.domain.User["userAddresses"]->

org.hibernate.collection.internal.PersistentBag[0]->

demo.server.core.domain.UserAddress["user"]->

......//无限递归

java.lang.*Error: null

    at java.lang.ClassLoader.defineClass1(Native Method) ~[na:1.8.0_111]

    at java.lang.ClassLoader.defineClass(Unknown Source) ~[na:1.8.0_111]

    at java.security.SecureClassLoader.defineClass(Unknown Source) ~[na:1.8.0_111]

    at java.net.URLClassLoader.defineClass(Unknown Source) ~[na:1.8.0_111]

    at java.net.URLClassLoader.access$100(Unknown Source) ~[na:1.8.0_111]

    at java.net.URLClassLoader$1.run(Unknown Source) ~[na:1.8.0_111]

    at java.net.URLClassLoader$1.run(Unknown Source) ~[na:1.8.0_111]

    at java.security.AccessController.doPrivileged(Native Method) ~[na:1.8.0_111]

    at java.net.URLClassLoader.findClass(Unknown Source) ~[na:1.8.0_111]

    at java.lang.ClassLoader.loadClass(Unknown Source) ~[na:1.8.0_111]

    at sun.misc.Launcher$AppClassLoader.loadClass(Unknown Source) ~[na:1.8.0_111]

    at java.lang.ClassLoader.loadClass(Unknown Source) ~[na:1.8.0_111]

    at com.fasterxml.jackson.databind.ser.std.BeanSerializerBase.serializeFields(BeanSerializerBase.java:709) ~[jackson-databind-2.8.1.jar:2.8.1]

    at com.fasterxml.jackson.databind.ser.BeanSerializer.serialize(BeanSerializer.java:155) ~[jackson-databind-2.8.1.jar:2.8.1]

    at com.fasterxml.jackson.databind.ser.std.CollectionSerializer.serializeContents(CollectionSerializer.java:149) ~[jackson-databind-2.8.1.jar:2.8.1]

    at

...

看异常的名字会发现是栈溢出，而且第一处后面出现大量的递归的提示，这边的原因是因为使用了jpa的实体类注解@ManyToMany,@ManyToOne,@OneToOne并且是双向表关联

举个例子：

@Entity

@Table(name = "t_student")

public class Student{

    @Id

    @GeneratedValue

    private Integer sId;

    @Column(length = 20)

    private String sName;

    //学生所修课程

    @ManyToMany(mappedBy = "students")

    private List<Course> courses;

    //get、set 方法省略

}



@Entity

@Table(name = "t_course")

public class Course{

    @Id

    @GeneratedValue

    private Integer cId;

    @Column(length = 20)

    private String cName;

    //上课的学生

    @ManyToMany(cascade = CascadeType.ALL)

    private List<Student> students;

    //get、set 方法省略

}

一个student类和一个course类分别对应 t_student 表和 t_course表,它们是多对多的关系，一个学生可以修多个课程，一个课程可以有多个学生修

省略仓储层代码…

控制层代码

@RestController

public class TestController{

    @Autowired

    private StudentRepository studentRep;

    @RequestMapping("/test")

    public int test(){

        List<Student> students = stntRep.findAll();

        students.forEach(data->{

            System.out.println(data);

        });

        return 1;

    }

}

此时，程序运行便会报 java.lang.*Error: null 异常

java.lang.*Error: null

    at java.util.AbstractCollection.toString(Unknown Source) ~[na:1.8.0_111]

    at org.hibernate.collection.internal.PersistentBag.toString(PersistentBag.java:510) ~[hibernate-core-5.0.12.Final.jar:5.0.12.Final]

    at java.lang.String.valueOf(Unknown Source) ~[na:1.8.0_111]

    at java.lang.StringBuilder.append(Unknown Source) ~[na:1.8.0_111]

    at com.demo.domain.Course.toString(Course.java:38) ~[classes/:na]

    at java.lang.String.valueOf(Unknown Source) ~[na:1.8.0_111]

    at java.lang.StringBuilder.append(Unknown Source) ~[na:1.8.0_111]

    at java.util.AbstractCollection.toString(Unknown Source) ~[na:1.8.0_111]

    at org.hibernate.collection.internal.PersistentBag.toString(PersistentBag.java:510) ~[hibernate-core-5.0.12.Final.jar:5.0.12.Final]

    at java.lang.String.valueOf(Unknown Source) ~[na:1.8.0_111]

    at java.lang.StringBuilder.append(Unknown Source) ~[na:1.8.0_111]

    at com.demo.domain.Student.toString(Student.java:40) ~[classes/:na]

    ....

Student类中有一个字段List<Course> courses，在遍历集合中，输出一个student实例的时候，List<Course> courses 字段也将输出，因为是双向多对多的关联查询，每一个Course实例也会输出List<Student> students 字段值，因此一直递归下去直到栈溢出报错，若是单向多对多就不会发生这样地递归

其实一开始报这个错完全是因为对spring-data-jpa不熟悉，了解之后一想就通了。

解决办法：

方法一：

此处，若不需要查看关联表中的字段信息时，可以在遍历List<Student> students集合时先将关联对象设置为null,即：

students.forEach(data->{

    data.setCourses(null);

    System.out.println(data);

});

这样才能打印出Student 实例中除了courses 字段之外地所有数据

方法二：

取消使用双向多对多关联，改为使用单向多对多，这样也可以同时将关联表中所对应的数据查询出来使用

原文地址：https://blog.****.net/pbhLOVEpp/article/details/77945651

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