How to convert Map of class objects to json java

Question

I have class with some properties, for example:

public class MyClass {
    public int number;
    public String s;
}

and I want to convert Map of this class to json. for example:

Map<String, MyClass> map = new HashMap();
map.put("sss", new MyClass(1, "blabla");

json j = new json(map);

and I want the output to be like:

{"sss":{"number":"1","s":"blabla"}}

someone know how to do that in JAVA? I tried with JSONObject and with Gson but did not work for me.

Have you already considered using Jackson-Mapper? - http://jackson.codehaus.org/ — pklndnst, May 04 '15 at 13:13
@PatrickOutOfBounds, Can you give me example how to do that with Jackson-Mapper because I did not succeeded to do that. maybe your example will help me. — chani, May 04 '15 at 13:15

Alok Mishra · Answer 1 · 2015-05-04T13:43:00.300

you can use toJson() method of Gson class to convert a java object to json ,see the example below ,

public class SomeObject {

    private int data1 = 100;
    private String data2 = "hello";
    private List<String> list = new ArrayList<String>() {
      {
        add("String 1");
        add("String 2");
        add("String 3");
      }
    };

    //getter and setter methods

    @Override
    public String toString() {
       return "SomeObject [data1=" + data1 + ", data2=" + data2 + ", list="
        + list + "]";
    }

}

i will convert the above class' object to json , getter and setter methods are useful when you are converting the json back to java object .

public static void main(String[] args) {

        SomeObject obj = new SomeObject();
        Gson gson = new Gson();

        // convert java object to JSON format,
        // and returned as JSON formatted string
        String json = gson.toJson(obj);
        System.out.println(json);

        }

output :

{"data1":100,"data2":"hello","list":["String 1","String 2","String 3"]}

when I used this object I need to case the MyClass object to String befor putting it into the JSONObject object (using gson for exapmle) and then the output with be something like: {"sss":"{\"number\":1,\"s\":\"test\"}"} so it is not good for me... — chani, May 04 '15 at 13:29
i have edited my answer , now its using Gson and you dont have to convert anything to string. @chani — Alok Mishra, May 04 '15 at 13:50

score 0 · Answer 2 · answered May 04 '15 at 13:16

0

Using Gson:

Gson gson = new GsonBuilder().create();
String json = gson.toJson(map);

answered May 04 '15 at 13:16

Hussein Zawawi

2,907
2
26
44

I tried it but the json string output was: {"message":"java.lang.Class cannot be cast to java.lang.reflect.ParameterizedType","code":1} – chani May 04 '15 at 13:21

score 0 · Answer 3 · answered May 04 '15 at 13:23

0

You have to fix, parenthesis issue.

map.put("sss", new MyClass(1,"test")); //observe 2 braces at the end!

Following code should do the trick for you,

Gson gson = new Gson();
String myJson = gson.toJson(map);

Output:

{"sss":{"number":1,"s":"test"}}

answered May 04 '15 at 13:23

Abhishek

6,912
14
59
85

the (...) was just an example. I fixed the question. and you answer is the same of the previous answer. when I did it- I got this json string: {"message":"java.lang.Class cannot be cast to java.lang.reflect.ParameterizedType","code":1} – chani May 04 '15 at 13:26
Please look into http://stackoverflow.com/questions/4226738/using-generics-with-gson – Abhishek May 04 '15 at 13:28
The link you gave me is how to deserialize and I am looking for way to serialize... – chani May 04 '15 at 13:50
Can you please share your code? We can look inito it and get back with solution – Abhishek May 04 '15 at 13:51

score 0 · Answer 4 · answered May 04 '15 at 13:32

Implement some custom toJSON() method for each class as shown below:

public class MyClass1 {
    String number;
    String name;

    public MyClass1(String number, String name){
        this.number = number;
        this.name = name;
    }

    public JSONObject toJSON() throws JSONException {
        return new JSONObject("{\"number\" : \""+this.number+"\", \"name\":\""+this.name+"\"}");
    }

}

And then just use it to convert your map to jsonObject:

public class MapToJSON {
    public static void main(String[] args) throws JSONException {
        Map<String, JSONObject> map = new HashMap<String, JSONObject>();
        map.put("sss", new MyClass1("1", "Hello").toJSON());

        System.out.println(new JSONObject(map));
    }
}

this answer good for small class. but if my class have more then 15 members.... If I will not fine another way to do that. this is what I will do. but I hope to fine cleaner way... — chani, May 04 '15 at 13:34

chani · Accepted Answer · 2015-05-04T14:54:50.050

I found the way how to do that:

import com.google.gson.Gson;
import org.json.JSONObject;

Gson gson = new Gson();

map.put("sss", new JSONObject(gson.toJson(new MyClass(1, "Hello"))));
map.put("aaa", new JSONObject(gson.toJson(new MyClass(2, "blabla"))));

String output = new JSONObject(map).toString();

and now the output is correct.

Thanks a lot to all the people that tried to help me with this problem...

How to convert Map of class objects to json java

5 Answers5