Convert JSON data to a list of Java objects

Question

I have JSON data like that:

[ {
    "data": "data",
    "what": "what2",
    "when": 1392046352,
    "id": 13,
    "tags": "checkid:testcheckid, target:server.id.test, id:testid"
}, {
    "data": "Test",
    "what": "Test",
    "when": 1395350977,
    "id": 5,
    "tags": "checkid:testcheckid, target:server.id.test, id:testid"
} ]

I have a Java class and I want to convert this JSON to a list of instances of my class. I found how to convert a single object, but not a list.

Answer 1

With Jackson you would do something like:

String jsonStr = "...";
ObjectReader reader = new ObjectMapper().reader();
List<Map<String, Object>> objs = reader.readValue(jsonStr);

Map<String, Object> myFirstObj = objs.get(0);
myFirstObj.get("data");
myFirstObj.get("what");
// and so on

Or even better you can create a pojo and do:

String jsonStr = "...";
ObjectMapper mapper = new ObjectMapper();
List<MyPojo> myObjs = mapper.readValue(jsonStr, new TypeReference<List<MyPojo>>() {});
MyPojo myPojo = myObjs.get(0);
myPojo.getData();
myPojo.getWhat();
// and so on

Answer 2

There are several libraries out there that will parse JSON, such as GSon and Jackson. If the functionality isn't provided out-of-box, you can write a custom deserializer that will do what you need.

Answer 3

I don't really understand your problem, if you already have and object just create a list (ArrayList for example) and add them.

ArrayList<YourObject> list = new ArrayList<YourObject>();
list.add(yourObject);