GSON - Creating JSON tree structure from Java

Question

Have a couple questions, using GSON. I have a feeling that GSON might not be what I am looking for in terms of a library that will be able to give me a JSON object that I can use later.

I am reading data from a database to populate a json object that I will later use. The output of the json object should look similar to the json below, which involves parents and children. It forms a small tree based structure:

var json = { 
         id: "1", 
         name: "Joe Smith", 
         data: { 
         "email": "",
         "phone": "123-123-1233"},
         children: [{
                        id: "Tim Anderson",
                        name: "Tim Anderson",
                        data: { 
                             "email": "[email protected]",
                             "phone": "123-123-1233"
                        },
                        children: []
                    },{
                        id: "Christopher Johnson",
                        name: "Christopher Johnson",
                        data: {  
                             "email": "[email protected]",
                             "phone": "123-123-1233"
                        },
                        children: []
                    },{
                        id: "Kate Green",
                        name: "Kate Green",
                        data: {

                        },
                        children: [{
                            id: "Gary Jones",
                            name: "Gary Jones",
                            data: {},
                            children: []
                        }, {
                            id: "Melissa Brand",
                            name: "Melissa Brand",
                            data: {},
                            children: []
                        }]
                    }
                    ] 
    }

How do I create a GSON object, similar to the structure above, that I can serialize to JSON that has this type of hierarchy? I've tried using maps and other collections - but I am having difficulty getting the results I want. Hence why I ask if GSON is what I really want for a JSON serialization.

Community · Accepted Answer · 2017-05-23 12:21:42Z

Have you tried the default java JSONTokener and other similar parsers?

      BufferedReader reader = new BufferedReader(new FileReader("jsonfile.json"));
     StringBuilder builder=new StringBuilder();
     for(String line=null;(line = reader.readLine()) != null;){
     builder.append(line).append("\n");
     }
    JSONTokener jsonTokener=new JSONTokener(builder.toString());
    JSONObject finalJson=new JSONObject(jsonTokener);

In your case if you want to find additional data in a hierarchy inside, then iterate over as follows

 JSONArray children=finalJson.getJSONArray("children");
 for(int i = 0;i<children.length;i++){
 JSONObject childRecData = children.getJSONObject(i); //returns the ith JSONObject containing id, name, data, etc.
 int id = childRecData.getString();
 String name = childRecData.getString();
 JSONObject data = childRecData.getJSONObject(0);
 }

NOTE That for larger JSON files (files which have ridiculous levels of hierarchy) such as an HTTP database requests GSON's POJO (Plain Old Java Objects) model as suggested by Nishant is recommended

Here's more information

Here was a similar question

Nishant · Accepted Answer · 2012-06-25 17:54:47Z

1

Let me give you a hint

make a Person and a Data class (POJO) like this

Person
  String id
  String name
  Data data
  List<Person> children

Data
  String email
  String phone

answered Jun 25, 2012 at 17:54

Nishant

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3 Comments

user82302124 Over a year ago

Thanks - I see that I can use POJO objects to create instances of nodes in a tree. Can I use these objects without problem in a GSON serialization?

Nishant Over a year ago

@K82_Med yes. You can use them to serialize and deserialize, both.

user82302124 Over a year ago

Thank you - I've got an idea where I am going thanks to your answer. Thanks for the tip.

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