关于java：json转换期间的stackoverflow错误（休眠双向映射）


stackoverflow error during json conversion (hibernate bi-directional mapping)

我有两个实体类：带问题列表的User类和带用户属性的Question类。

用户类声明：

1
2
3
4
5
6
7
8
9
10
11
12
 @Entity
    @Table(schema="test",name="so_user")
    public class User {
    private List<Question> questions;
    //other attributes
            @OneToMany(cascade=CascadeType.ALL)
        @PrimaryKeyJoinColumn  
        public List<Question> getQuestions() {
            return questions;
        }
    //.. other methods
    }

问题类声明：

1
2
3
4
5
6
7
8
9
10
11
12
13
@Entity
@Table(schema="test")
public class Question {
private User askedBy;
//other attributes
  @ManyToOne(cascade=CascadeType.ALL,fetch=FetchType.EAGER)
  @PrimaryKeyJoinColumn
  public User getAskedBy() {
    return askedBy;
  }

//.. other methods
}

号

当我试图使用Gson library将用户对象转换为json时，它给出了stackoverflow error。原因：用户有一个问题列表，每个问题依次有用户属性(用于在休眠状态下具有双向映射)。

测试代码：

1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
public class MappingTest {
    public static void main(String[] args) {
        List<User> users = null;
        User user = null;
        //populate some users
        for (int i = 0; i < 10; i++) {
            if (i == 0)
                users = new ArrayList<User>();
            user = new User();
            List<Question> questions = null;
            Question question = null;
            //create dummy questions
            for (int questionCount = 0; questionCount < 5; questionCount++) {
                if(questionCount==0)
                    questions = new ArrayList<Question>();
                question = new Question();
                question.setAskedBy(user);
                System.out.println("question added is"+question);
                questions.add(question);
            }
            user.setQuestions(questions);
            users.add(user);
            System.out.println("user added is"+user);
        }
        //TODO
        System.out.println(users);
        Gson gson = new Gson();
        System.out.println(gson.toJson(users));

    }
}

控制台日志：

1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
Exception in thread"main" java.lang.StackOverflowError
    at java.lang.AbstractStringBuilder.append(Unknown Source)
    at java.lang.StringBuffer.append(Unknown Source)
    at java.io.StringWriter.write(Unknown Source)
    at com.google.gson.stream.JsonWriter.string(JsonWriter.java:534)
    at com.google.gson.stream.JsonWriter.writeDeferredName(JsonWriter.java:402)
    at com.google.gson.stream.JsonWriter.value(JsonWriter.java:495)
    at com.google.gson.internal.bind.TypeAdapters$8.write(TypeAdapters.java:268)
    at com.google.gson.internal.bind.TypeAdapters$8.write(TypeAdapters.java:253)
    at com.google.gson.internal.bind.TypeAdapterRuntimeTypeWrapper.write(TypeAdapterRuntimeTypeWrapper.java:68)
    at com.google.gson.internal.bind.ReflectiveTypeAdapterFactory$1.write(ReflectiveTypeAdapterFactory.java:89)
    at com.google.gson.internal.bind.ReflectiveTypeAdapterFactory$Adapter.write(ReflectiveTypeAdapterFactory.java:195)
    at com.google.gson.internal.bind.TypeAdapterRuntimeTypeWrapper.write(TypeAdapterRuntimeTypeWrapper.java:68)
    at com.google.gson.internal.bind.CollectionTypeAdapterFactory$Adapter.write(CollectionTypeAdapterFactory.java:96)
    at com.google.gson.internal.bind.CollectionTypeAdapterFactory$Adapter.write(CollectionTypeAdapterFactory.java:60)
    at com.google.gson.internal.bind.TypeAdapterRuntimeTypeWrapper.write(TypeAdapterRuntimeTypeWrapper.java:68)
    at com.google.gson.internal.bind.ReflectiveTypeAdapterFactory$1.write(ReflectiveTypeAdapterFactory.java:89)
    at com.google.gson.internal.bind.ReflectiveTypeAdapterFactory$Adapter.write(ReflectiveTypeAdapterFactory.java:195)
    at com.google.gson.Gson$FutureTypeAdapter.write(Gson.java:892)
    at com.google.gson.internal.bind.TypeAdapterRuntimeTypeWrapper.write(TypeAdapterRuntimeTypeWrapper.java:68)
    at com.google.gson.internal.bind.ReflectiveTypeAdapterFactory$1.write(ReflectiveTypeAdapterFactory.java:89)
    at com.google.gson.internal.bind.ReflectiveTypeAdapterFactory$Adapter.write(ReflectiveTypeAdapterFactory.java:195)
    at com.google.gson.internal.bind.TypeAdapterRuntimeTypeWrapper.write(TypeAdapterRuntimeTypeWrapper.java:68)
    at com.google.gson.internal.bind.CollectionTypeAdapterFactory$Adapter.write(CollectionTypeAdapterFactory.java:96)
    at com.google.gson.internal.bind.CollectionTypeAdapterFactory$Adapter.write(CollectionTypeAdapterFactory.java:60)
    at com.google.gson.internal.bind.TypeAdapterRuntimeTypeWrapper.write(TypeAdapterRuntimeTypeWrapper.java:68)
    at com.google.gson.internal.bind.ReflectiveTypeAdapterFactory$1.write(ReflectiveTypeAdapterFactory.java:89)
    at com.google.gson.internal.bind.ReflectiveTypeAdapterFactory$Adapter.write(ReflectiveTypeAdapterFactory.java:195)
    at com.google.gson.Gson$FutureTypeAdapter.write(Gson.java:892)
    at com.google.gson.internal.bind.TypeAdapterRuntimeTypeWrapper.write(TypeAdapterRuntimeTypeWrapper.java:68)
    at com.google.gson.internal.bind.ReflectiveTypeAdapterFactory$1.write(ReflectiveTypeAdapterFactory.java:89)
    at com.google.gson.internal.bind.ReflectiveTypeAdapterFactory$Adapter.write(ReflectiveTypeAdapterFactory.java:195)
    at com.google.gson.internal.bind.TypeAdapterRuntimeTypeWrapper.write(TypeAdapterRuntimeTypeWrapper.java:68)
    at com.google.gson.internal.bind.CollectionTypeAdapterFactory$Adapter.write(CollectionTypeAdapterFactory.java:96)
    at com.google.gson.internal.bind.CollectionTypeAdapterFactory$Adapter.write(CollectionTypeAdapterFactory.java:60)
    at com.google.gson.internal.bind.TypeAdapterRuntimeTypeWrapper.write(TypeAdapterRuntimeTypeWrapper.java:68)
    at com.google.gson.internal.bind.ReflectiveTypeAdapterFactory$1.write(ReflectiveTypeAdapterFactory.java:89)
    at com.google.gson.internal.bind.ReflectiveTypeAdapterFactory$Adapter.write(ReflectiveTypeAdapterFactory.java:195)
    at com.google.gson.Gson$FutureTypeAdapter.write(Gson.java:892)
    at com.google.gson.internal.bind.TypeAdapterRuntimeTypeWrapper.write(TypeAdapterRuntimeTypeWrapper.java:68)
    at com.google.gson.internal.bind.ReflectiveTypeAdapterFactory$1.write(ReflectiveTypeAdapterFactory.java:89)
    at com.google.gson.internal.bind.ReflectiveTypeAdapterFactory$Adapter.write(ReflectiveTypeAdapterFactory.java:195)
    at com.google.gson.internal.bind.TypeAdapterRuntimeTypeWrapper.write(TypeAdapterRuntimeTypeWrapper.java:68)
    at com.google.gson.internal.bind.CollectionTypeAdapterFactory$Adapter.write(CollectionTypeAdapterFactory.java:96)
    at com.google.gson.internal.bind.CollectionTypeAdapterFactory$Adapter.write(CollectionTypeAdapterFactory.java:60)
    at com.google.gson.internal.bind.TypeAdapterRuntimeTypeWrapper.write(TypeAdapterRuntimeTypeWrapper.java:68)
    at com.google.gson.internal.bind.ReflectiveTypeAdapterFactory$1.write(ReflectiveTypeAdapterFactory.java:89)
    at com.google.gson.internal.bind.ReflectiveTypeAdapterFactory$Adapter.write(ReflectiveTypeAdapterFactory.java:195)
    at com.google.gson.Gson$FutureTypeAdapter.write(Gson.java:892)
    at com.google.gson.internal.bind.TypeAdapterRuntimeTypeWrapper.write(TypeAdapterRuntimeTypeWrapper.java:68)
    at com.google.gson.internal.bind.ReflectiveTypeAdapterFactory$1.write(ReflectiveTypeAdapterFactory.java:89)
    at com.google.gson.internal.bind.ReflectiveTypeAdapterFactory$Adapter.write(ReflectiveTypeAdapterFactory.java:195)
    at com.google.gson.internal.bind.TypeAdapterRuntimeTypeWrapper.write(TypeAdapterRuntimeTypeWrapper.java:68)
    at com.google.gson.internal.bind.CollectionTypeAdapterFactory$Adapter.write(CollectionTypeAdapterFactory.java:96)
    at com.google.gson.internal.bind.CollectionTypeAdapterFactory$Adapter.write(CollectionTypeAdapterFactory.java:60)
    at com.google.gson.internal.bind.TypeAdapterRuntimeTypeWrapper.write(TypeAdapterRuntimeTypeWrapper.java:68)
    at com.google.gson.internal.bind.ReflectiveTypeAdapterFactory$1.write(ReflectiveTypeAdapterFactory.java:89)
    at com.google.gson.internal.bind.ReflectiveTypeAdapterFactory$Adapter.write(ReflectiveTypeAdapterFactory.java:195)

。

相关讨论

将jackson API放入(com.fasterxml.jackson)应用程序中，并在reationship中使用此注释

@对反向类的jsonbackreference(案例1到n中的列表或集合)。

@JSONManagedReference到MappedBy类(案例1到N中的单个对象)。

在你的情况下

1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
@OneToMany(cascade=CascadeType.ALL)
@PrimaryKeyJoinColumn
@JsonManagedReference  
public List<Question> getQuestions() {
     return questions;
}

______________________________________


@ManyToOne(cascade=CascadeType.ALL,fetch=FetchType.EAGER)
@PrimaryKeyJoinColumn
@JsonBackReference
public User getAskedBy() {
    return askedBy;
}

您需要与Jackson(而不是GSON)一起打印JSON。

它与我一起使用双向递归进行序列化。

相关讨论