java-2.0.4版本不支持双向链表的json字符串转实体类，双向链表转json会有问题

[javalipf]

`@Data
public class ApproveConfigJson implements Serializable {
private String postId;

private boolean hasPreNode = false;

private ApproveConfigJson preNode;

private boolean hasNextNode = false;

private ApproveConfigJson nextNode;

}`

json字符串 {"hasNextNode":true,"hasPreNode":false,"jump":true,"nextNode":{"hasNextNode":true,"hasPreNode":true,"jump":true,"nextNode":{"hasNextNode":false,"hasPreNode":true,"jump":true,"passType":1,"postId":"8422e7b960781225747439c620cd0919","preNode":{"$ref":".."},"sort":3},"passType":1,"postId":"1e1e159ad5f8293124208207aa4b76b1","preNode":{"$ref":".."},"sort":2},"passType":1,"postId":"b68aac95774a9682aeddb9a2d15a0c38","preNode":{"hasNextNode":false,"hasPreNode":false,"jump":false,"sort":0},"sort":1}

使用JSON.parseObject(str, ApproveConfigJson.class);方法生成的ApproveConfigJson，在链表第二级节点及之后，无法正确追踪到前一级节点，而这在1.2.78版本是可用的
另外双向链表结构转json字符串的过程会栈内存溢出

[javalipf]

2.0.5版本，双向链表向Json序列化可用，但是序列化产生的数据反序列化节点存在问题，如下
`@Data
@NoArgsConstructor
@AllArgsConstructor
public class ApproveConfigJson implements Serializable {
private String postId;

private boolean hasPreNode = false;

private ApproveConfigJson preNode;

private boolean hasNextNode = false;

private ApproveConfigJson nextNode;

private int sort;

public ApproveConfigJson(String postId, int sort) {
    this.postId = postId;
    this.sort = sort;
}

}
public static void main(String[] args) {
List approveConfigJsons = new ArrayList<>();
approveConfigJsons.add(new ApproveConfigJson("1",1));
approveConfigJsons.add(new ApproveConfigJson("2",2));
approveConfigJsons.add(new ApproveConfigJson("3",3));
String s = list2LinkedJson2(approveConfigJsons);
ApproveConfigJson approveConfigJson = JSON.parseObject(s, ApproveConfigJson.class);
System.err.println(approveConfigJson.getNextNode().getPreNode().getPostId());
}

public static String list2LinkedJson2(List<ApproveConfigJson> approveConfigJsons) {
    approveConfigJsons = approveConfigJsons.stream().sorted(Comparator.comparing(ApproveConfigJson::getSort)).collect(Collectors.toList());
    ApproveConfigJson approveUtil = null;
    Iterator<ApproveConfigJson> iterator = approveConfigJsons.iterator();
    ApproveConfigJson local = new ApproveConfigJson();
    while (iterator.hasNext()) {
        ApproveConfigJson next = iterator.next();
        if (approveUtil == null) {
            approveUtil = next;
            local = next;
        } else {
            approveUtil.setHasNextNode(true);
            approveUtil.setNextNode(next);
            next.setHasPreNode(true);
            next.setPreNode(local);
            local = next;
            approveUtil = approveUtil.getNextNode();
            approveUtil.setNextNode(null);
        }
    }

    ApproveConfigJson finalNode = approveUtil;
    while (finalNode.isHasPreNode()) {
        finalNode = finalNode.getPreNode();
    }
    return JSON.toJSONString(finalNode);
}`

按照sort排序，链表首节点为postId = 1，序列化的json串正常，但是反序列化后链表的首节点为postId = 2，且获取下级节点后再获取上级节点会出现java.lang.NullPointerException
在 ApproveConfigJson approveConfigJson = JSON.parseObject(s, ApproveConfigJson.class);方法中

[wenshao]

https://github.com/alibaba/fastjson2/releases/tag/2.0.6
问题已经修复，请用新版本