How do create a formatted json with Java?

Question

So given these arbitrary variables

String name = "bob";
List<String> hobby = new ArrayList<String>();
hobby.add("walk");
hobby.add("gym");
hobby.add("football");

How do I output a String json? Example of above

{
    "name": "bob",
    "hobby": [
        "walk",
        "gym",
        "football"
    ]

}

I've tried JSONObject json = new JSONObject(); but with that it wasn't properly formatted the way I wanted.

Answer 1

As far as I know, you have to handle the list - hobby - by yourself to print it with newline. But with the help of Gson (Google Gson), you can print them as you expected as follows.

JSONObject jsonObj = new JSONObject();
jsonObj.put("name", name);
jsonObj.put("hobby", hobby);

JsonParser parser = new JsonParser();
JsonObject json = parser.parse(jsonObj.toString()).getAsJsonObject();
Gson gson = new GsonBuilder().setPrettyPrinting().create();
System.out.println(gson.toJson(json));

Then the console out is going to be

{
  "name": "bob",
  "hobby": [
    "walk",
    "gym",
    "football"
  ]
}

UPDATED

If you use writerWithDefaultPrettyPrinter() in Jackson2 library, it seems not to print Json array as same as Gson .

ObjectMapper mapper = new ObjectMapper();
Object jsonObj1 = mapper.readValue(jsonObj.toString(), Object.class);
System.out.println(mapper.writerWithDefaultPrettyPrinter().writeValueAsString(jsonObj1));

Console output:

{
  "name" : "bob",
  "hobby" : [ "walk", "gym", "football" ]
}

Answer 2

If you use fasterxml jackson, it would be very easy.
UPD1: output with default pretty printer.

@Test
public void test01() {

    String name = "bob";
    List<String> hobby = new ArrayList<String>();
    hobby.add("walk");
    hobby.add("gym");
    hobby.add("football");

    // create a class with name and hobby property
    Demo demo = new Demo();
    demo.setName(name);
    demo.setHobby(hobby);
    ObjectMapper objectMapper = new ObjectMapper();
    try {
        String result = objectMapper.writeValueAsString(demo);
        System.out.println(result);
        //{"name":"bob","hobby":["walk","gym","football"]}
        String prettyResult = objectMapper.writerWithDefaultPrettyPrinter().writeValueAsString(demo);
        System.out.println(prettyResult);
//            {
//                "name" : "bob",
//                "hobby" : [ "walk", "gym", "football" ]
//            }
    } catch (JsonProcessingException e) {
        e.printStackTrace();
    }
}

static class Demo {
    private String name;
    private List<String> hobby;
    //getter/setter
}