Can I deserialize a json in recursive manner by including parent class in child class?

Question

I have a json something like

{
    "author":"jack",
    "comment_body":"any message body",
    "replies":{
        "author":"john",
        "comment_body":" reply body",
        "replies": {
            "author":"john",
        "comment_body":" reply body",
        "replies":{
            ...
        }
        }
    }
}

how can I parse this json so far my classes are

class Comment {
private String author;
private String comment_body;
private Replies replies;
}

class Replies{
private Comment comment_tree;
}

Any help on how to parse comment response in gson ?

score 1 · Accepted Answer · answered Oct 16 '18 at 16:06

You don't need Replies class. It doesn't match your JSON. You have one recursive class here.

First of all, you need to edit your JSON a little, for example (added null):

{
    "author": "Jack",
    "comment_body": "Any message body",
    "replies": {
        "author": "John",
        "comment_body": "Reply body",
        "replies": {
            "author": "Smith",
            "comment_body": "Another reply body",
            "replies": null
        }
    }
}

Next, make a recursive variable in your class:

public class Comment {
    String author;
    String comment_body;
    Comment replies;

    @Override
    public String toString() {
        return "Comment{author='" + author + "', comment_body='" + comment_body + "', replies=" + replies + '}';
    }
}

Finally, the runnable class:

import com.google.gson.Gson;

public class Main {
    public static void main (String[] args) {
        String json =   "{\n" +
                        "    \"author\": \"Jack\",\n" +
                        "    \"comment_body\": \"Any message body\",\n" +
                        "    \"replies\": {\n" +
                        "        \"author\": \"John\",\n" +
                        "        \"comment_body\": \"Reply body\",\n" +
                        "        \"replies\": {\n" +
                        "            \"author\": \"Smith\",\n" +
                        "            \"comment_body\": \"Another reply body\",\n" +
                        "            \"replies\": null\n" +
                        "        }\n" +
                        "    }\n" +
                        "}\n";
         Comment comment = new Gson().fromJson(json, Comment.class);
         System.out.println(comment);
    }
}

Output:

Comment{author='Jack', comment_body='Any message body', replies=Comment{author='John', comment_body='Reply body', replies=Comment{author='Smith', comment_body='Another reply body', replies=null}}}

is it okay to use same class reference as you used for reply ? — John McLane, Oct 16 '18 at 22:37
Sure. `private static class Node` inside `java.util.LinkedList` implementation made the same way. — , Oct 17 '18 at 04:55
Hey I used your method. Now I'm getting another problem. Is there any way to invoke default gson deserializer in JsonDeserializer ? — John McLane, Oct 17 '18 at 08:05
[Maybe this will help](https://stackoverflow.com/questions/10596667/how-to-invoke-default-deserialize-with-gson) — , Oct 17 '18 at 11:07

score 0 · Answer 2 · answered Oct 16 '18 at 05:17

0

You will need reflection to do that... But you really should consider using an existing library such as Jackson, which has ObjectMapper that does this job for you.

Here is a link to the basics of using Jackson to serialize / deserialize objects to and from JSON.

https://www.baeldung.com/jackson-object-mapper-tutorial

Hope it helps!

answered Oct 16 '18 at 05:17

Tomaz Fernandes

2,429
2
14
18

Actually I want to do it in gson – John McLane Oct 16 '18 at 05:25
Then perhaps this answer will help you. https://stackoverflow.com/questions/28391982/how-to-use-gson-to-serialize-objects-in-android – Tomaz Fernandes Oct 16 '18 at 05:31
It says android but it holds for any java application. – Tomaz Fernandes Oct 16 '18 at 05:31
1

thanks for your help, but that's not what I'm looking for :) – John McLane Oct 16 '18 at 06:02

Kishita Variya · Answer 3 · 2018-10-17T09:04:14.687

You just need Comment class. Try this:

class Comment {
    private String author;
    private String comment_body;
    private Comment replies;
}

Sample Code:

public class Main {

    public static void main(String[] args) {
        Comment comment = new Comment();
        comment.setAuthor("Outer Author");
        comment.setReplies(new Comment());
        comment.getReplies().setAuthor("Inner Author");

        System.out.println("Author 1 :"+comment.getAuthor());
        System.out.println("...Author 2 :"+comment.getReplies().getAuthor());
    }
}

class Comment {
    private String author;
    private String comment_body;
    private Comment replies;

    public String getAuthor() {
        return author;
    }

    public void setAuthor(String author) {
        this.author = author;
    }

    public String getComment_body() {
        return comment_body;
    }

    public void setComment_body(String comment_body) {
        this.comment_body = comment_body;
    }

    public Comment getReplies() {
        return replies;
    }

    public void setReplies(Comment replies) {
        this.replies = replies;
    }
}

Sample output:

Author 1 :Outer Author
...Author 2 :Inner Author

how can I add class refrence in same class ?? I think its not possible — John McLane, Oct 16 '18 at 05:25

Can I deserialize a json in recursive manner by including parent class in child class?

3 Answers3