JSON-B的循环引用问题

Question

我有两门课互相引用。当我试图将类序列化到Json时，我会得到一个循环引用错误。有人能告诉我怎么改正吗？

我有一个包含密码列表的文件夹类：

public class Folder {

    private List<Password> items = new ArrayList<>();
    private String name;

    public Folder(String name) {
        this.name = name;
    }

    public void add(Password password) {
        items.add(password);
    }

    public List<Password> getItems() {
        return items;
    }

    public void setItems(List<Password> items) {
        this.items = items;
    }

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }       
}

然后，我有一个密码类，它引用文件夹类：

public class Password {

    private String name;
    private Folder mFolder;

    public Password(String name, Folder folder) {
        this.name = name;
        folder.add(this);
        mFolder = folder;       
    }

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

    public Folder getmFolder() {
        return mFolder;
    }

    public void setmFolder(Folder mFolder) {
        this.mFolder = mFolder;
    }    
}

最后是主修班：

public class Main {

    public static void main(String[] args) throws IOException {

        Password password = new Password("Password", new Folder("Folder"));

        Jsonb jsonb = JsonbBuilder.create();        
        try (Writer writer = new StringWriter()) {          
            jsonb.toJson(password, writer);
            System.out.println(writer.toString());
        }
    }    
}

获取以下异常：

at org.eclipse.yasson.internal.serializer.AbstractContainerSerializer.serialize(AbstractContainerSerializer.java:60)
    at org.eclipse.yasson.internal.serializer.AbstractContainerSerializer.serializerCaptor(AbstractContainerSerializer.java:91)
    at org.eclipse.yasson.internal.serializer.CollectionSerializer.serializeInternal(CollectionSerializer.java:76)
    at org.eclipse.yasson.internal.serializer.CollectionSerializer.serializeInternal(CollectionSerializer.java:35)
    at org.eclipse.yasson.internal.serializer.AbstractContainerSerializer.serialize(AbstractContainerSerializer.java:60)
    at org.eclipse.yasson.internal.serializer.AbstractContainerSerializer.serializerCaptor(AbstractContainerSerializer.java:91)
    at org.eclipse.yasson.internal.serializer.ObjectSerializer.marshallProperty(ObjectSerializer.java:92)
    at org.eclipse.yasson.internal.serializer.ObjectSerializer.serializeInternal(ObjectSerializer.java:59)

Answer 1

在Password或Folder中，您需要删除它们之间的引用(在序列化中)。您可以将@JsonbTransient用于您不希望在JSON中序列化的字段。

(文档：http://json-b.net/docs/user-guide.html#ignoring-properties)

示例：Password类方法

@JsonbTransient
private Folder mFolder;

示例：Folder类方法

@JsonbTransient
private List<Password> items = new ArrayList<>();

现在由您决定哪个类不会显示对另一个类的引用。此外，请参见this

Answer 2

当两个类相互引用时，会发生此问题。可以使用GSONBuilder使用setExclusionStrategies方法获取自定义gson对象。

GSON gsonObject = new GsonBuilder()
    .setExclusionStrategies(new ExclusionStrategy() {
     /** boolean method shouldSkipClass(Class<?> clz) */
     /** boolean method shouldSkipField(FieldAttributes field) */
});