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

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"
}