How to convert hashmap to JSON object in Java

Question

How to convert or cast hashmap to JSON object in Java, and again convert JSON object to JSON string?

Answer 1

For those using org.json.simple.JSONObject, you could convert the map to Json String and parse it to get the JSONObject.

JSONObject object = (JSONObject) new JSONParser().parse(JSONObject.toJSONString(map));

Answer 2

Gson can also be used to serialize arbitrarily complex objects.

Here is how you use it:

Gson gson = new Gson(); 
String json = gson.toJson(myObject); 

Gson will automatically convert collections to JSON arrays. Gson can serialize private fields and automatically ignores transient fields.

Answer 3

If you don't really need HashMap then you can do something like that:

String jsonString = new JSONObject() {{
  put("firstName", user.firstName);
  put("lastName", user.lastName);
}}.toString();

Output:

{
  "firstName": "John",
  "lastName": "Doe"
}

Answer 4

I'm using Alibaba fastjson, easy and simple:

<dependency>
    <groupId>com.alibaba</groupId>
    <artifactId>fastjson</artifactId>
    <version>VERSION_CODE</version>
</dependency>

and import:

import com.alibaba.fastjson.JSON;

Then:

String text = JSON.toJSONString(obj); // serialize
VO vo = JSON.parseObject("{...}", VO.class); //unserialize

Everything is ok.

Answer 5

If you need use it in the code.

Gson gsone = new Gson();
JsonObject res = gsone.toJsonTree(sqlParams).getAsJsonObject();

Answer 6

I found another way to handle it.

Map obj=new HashMap();    
obj.put("name","sonoo");    
obj.put("age",new Integer(27));    
obj.put("salary",new Double(600000));   
String jsonText = JSONValue.toJSONString(obj);  
System.out.print(jsonText);

Hope this helps.

Thanks.