spring-data-jpa雙向表關聯查詢時引發異常:java.lang.StackOverflowError: null
阿新 • • 發佈:2019-02-07
專案異常如下:
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 (StackOverflowError); nested exception is com.fasterxml.jackson.databind.JsonMappingException: Infinite recursion (StackOverflowError) (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"]->
......//無限遞迴
java.lang.StackOverflowError: 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
...
看異常的名字會發現是棧溢位,而且第一處後面出現大量的遞迴的提示,這邊的原因是因為使用了jpa的實體類註解@ManyToMany,@ManyToOne,@OneToOne並且是雙向表關聯
舉個例子:
@Entity
@Table(name = "t_student")
public class Student{
@Id
@GeneratedValue
private Integer sId;
@Column(length = 20)
private String sName;
//學生所修課程
@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;
//上課的學生
@ManyToMany(cascade = CascadeType.ALL)
private List<Student> students;
//get、set 方法省略
}
一個student類和一個course類分別對應 t_student 表和 t_course表,它們是多對多的關係,一個學生可以修多個課程,一個課程可以有多個學生修
省略倉儲層程式碼…
控制層程式碼
@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;
}
}
此時,程式執行便會報 java.lang.StackOverflowError: null 異常
java.lang.StackOverflowError: 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類中有一個欄位List<Course> courses
,在遍歷集合中,輸出一個student
例項的時候,List<Course> courses
欄位也將輸出,因為是雙向多對多的關聯查詢,每一個Course
例項也會輸出List<Student> students
欄位值,因此一直遞迴下去直到棧溢位報錯,若是單向多對多就不會發生這樣地遞迴
其實一開始報這個錯完全是因為對spring-data-jpa不熟悉,瞭解之後一想就通了。
解決辦法:
方法一:
此處,若不需要檢視關聯表中的欄位資訊時,可以在遍歷List<Student> students
集合時先將關聯物件設定為null
,即:
students.forEach(data->{
data.setCourses(null);
System.out.println(data);
});
這樣才能打印出Student
例項中除了courses
欄位之外地所有資料
方法二:
取消使用雙向多對多關聯,改為使用單向多對多,這樣也可以同時將關聯表中所對應的資料查詢出來使用