ArrayList> to JSON object Java

Question

I want to create a String as follows.

[{ "Name":"David",
    "Age":"30"
  },
  {"Name":"Max",
   "Age":"20"
  }
]

How can we create this string using ArrayList<HashMap<String,String>> and JSON in Java?

Answer 1

Try as below

public String listmap_to_json_string(List<HashMap<String, String>> list)
{       
    JSONArray json_arr=new JSONArray();
    for (Map<String, String> map : list) {
        JSONObject json_obj=new JSONObject();
        for (Map.Entry<String, String> entry : map.entrySet()) {
            String key = entry.getKey();
            String value = entry.getValue();
            try {
                json_obj.put(key,value);
            } catch (JSONException e) {
                // TODO Auto-generated catch block
                e.printStackTrace();
            }                           
        }
        json_arr.put(json_obj);
    }
    return json_arr.toString();
}

Answer 2

My JSON library fits your use case exactly. For example:

ArrayList<HashMap<String,String>> outer = new ArrayList<HashMap<String,String>>();

HashMap<String,String> inner = new HashMap<String,String>();
inner.put("Name", "David");
inner.put("Age", "30");
outer.add(inner);

inner = new HashMap<String,String>();
inner.put("Name", "Max");
inner.put("Age", "20");
outer.add(inner);

//----------

import io.nayuki.json.Json;
String jsonText = Json.serialize(outer);
System.out.println(jsonText);

Output text:

[{"Age": "30", "Name": "David"}, {"Age": "20", "Name": "Max"}]

Answer 3

Try Jackson Mapper You can read some tutorials about it. You can write code, using Jackson in this manner:

ObjectMapper mapper = new ObjectMapper();
jsonString = mapper.writeValueAsString(listOfMap);