How to create JSON string from POJO by using Jackson?

Question

I have the following output that i need to send to server from my application, but I don't know how to create it as a POJO. JSON structure is as follows:

[
  {
    "data_type": "gen_shifts",
    "data": [
        {
            "device_id": "121212",
            "shift_type": "12",
            "start_time": "",
            "end_time": "",
            "staff_card_no": "",
            "processed_date": ""
        },
        {
            "device_id": "121212",
            "shift_type": "12",
            "start_time": "",
            "end_time": "",
            "staff_card_no": "",
            "processed_date": ""
        }
    ]
},
{
    "data_type": "charge",
    "data": [
        {
            "card_no": "121212",
            "current_balance": "12",
            "sam_signature": "243453453453"
        },
        {
            "card_no": "7777",
            "current_balance": "32",
            "sam_signature": "243453453453"
        }
    ]
},
{
    "data_type": "shifts_types",
    "data": [
        {
            "type_id": "121212",
            "type_name": "12",
            "start_time": "243453453453",
            "end_time": ""
        },
        {
            "type_id": "121212",
            "type_name": "12",
            "start_time": "243453453453",
            "end_time": ""
        }
    ]
}
]

I cannot figure out how to create [] that 2 parantheses from my pojo to encapsulate all other fields.

Thanks for the help,

Answer 1

Like so :

public class WrapperArray extends ArrayList<DataWrapper> {
}

public class DataWrapper {
    @JsonProperty(value = "data_type")
    private String dataType;

    @JsonProperty(value = "data")
    private List<Data> data;

    // you need to add empty constructor and getters/setters
}

public abstract class Data {
}

public class GenShiftsData extends Data {
    @JsonProperty(value = "device_id")
    private String deviceId;

    @JsonProperty(value = "shift_type")
    private String shiftType;

    @JsonProperty(value = "start_time")
    private String startTime;

    @JsonProperty(value = "end_time")
    private String endTime;

    @JsonProperty(value = "staff_card_no")
    private String staffCardNo;

    @JsonProperty(value = "processed_date")
    private String processedDate;

    // you need to add empty constructor and getters/setters
}

And serialize a WrapperArray like that :

ObjectMapper mapper = new ObjectMapper();
WrapperArray wrapperArray = new WrapperArray();
wrapperArray.add(dataWrapper1);
wrapperArray.add(dataWrapper2);

String jsonResult = mapper.writeValueAsString(wrapperArray);