Parsing JSON Response using Jackson - web-services

Question

I have written a web-service and hosted in the following URL http://192.168.2.34:8081/MyWebService/facility/university
Response from this web service in JSON format is:
{
"university": [
{
"emailOfPrincipal": "prin1#gmail.com",
"labLists": [
{
"instrumentLists": [
{
"instrumentId": "1",
"instrumentName": "Instrument 1"
},
{
"instrumentId": "2",
"instrumentName": "instrument 2"
}
],
"labId": "11",
"labName": "Lab 11"
},
{
"instrumentLists": [
{
"instrumentId": "3",
"instrumentName": "instrument 3"
},
{
"instrumentId": "4",
"instrumentName": "instrument 4"
}
],
"labId": "22",
"labName": "Lab 22"
}
],
"univAddress": "Kolkata",
"univId": "111",
"univName": "University 111",
"univPrincipalName": "Principal 1"
},
{
"emailOfPrincipal": "prin2#gmail.com",
"labLists": [
{
"instrumentLists": [
{
"instrumentId": "5",
"instrumentName": "Instrument 5"
},
{
"instrumentId": "6",
"instrumentName": "Instrument 6"
}
],
"labId": "33",
"labName": "Lab 33"
},
{
"instrumentLists": [
{
"instrumentId": "7",
"instrumentName": "Instrument 7"
},
{
"instrumentId": "8",
"instrumentName": "Instrument 8"
}
],
"labId": "44",
"labName": "Lab 44"
}
],
"univAddress": "Bangalore",
"univId": "222",
"univName": "University 222",
"univPrincipalName": "Principal 2"
},
{
"emailOfPrincipal": "prin3#gmail.com",
"labLists": [
{
"instrumentLists": [
{
"instrumentId": "9",
"instrumentName": "Instrument 9"
},
{
"instrumentId": "10",
"instrumentName": "Instrument 10"
}
],
"labId": "55",
"labName": "Lab 55"
},
{
"instrumentLists": [
{
"instrumentId": "11",
"instrumentName": "Instrument 11"
},
{
"instrumentId": "12",
"instrumentName": "Instrument 12"
}
],
"labId": "66",
"labName": "Lab 66"
}
],
"univAddress": "Hyderabad",
"univId": "333",
"univName": "University 333",
"univPrincipalName": "Principal 3"
}
]
}
I am trying to convert JSON data into Java object using jackson api. But getting an error.
My Java Objects are:
University.java
public class University {
private int univId;
private String univName;
private String univAddress;
private String univPrincipalName;
private String emailOfPrincipal;
private List<Laboratory> labLists = new ArrayList<>();
//... Getter and Setter Methods...
}
Laboratory.java
public class Laboratory {
private int labId;
private String labName;
private List<Instruments> instrumentLists = new ArrayList<>();
//... Getter and Setter Methods...
}
Instruments.java
public class Instruments {
private int instrumentId;
private String instrumentName;
private String bookingStatus;
private Date bookingFrom;
private Date bookingTo;
private Date requestedTime;
//... Getter and Setter Methods...
}
The Client written is:
public class ParseJSONData {
public static void main(String[] args) throws ClientProtocolException, IOException {
String URL = "http://192.168.2.34:8081/MyWebService/facility/university";
DefaultHttpClient httpclient = new DefaultHttpClient();
HttpGet httpget = new HttpGet(URL);
HttpResponse response = httpclient.execute(httpget);
// System.out.println(response);
HttpEntity entity = response.getEntity();
String result = EntityUtils.toString(entity);
ObjectMapper mapper = new ObjectMapper();
University universities = mapper.readValue(result, University.class);
System.out.println(universities.getEmailOfPrincipal());
}
The error I am getting says
Exception in thread "main" org.codehaus.jackson.map.exc.UnrecognizedPropertyException: Unrecognized field "university" (Class University), not marked as ignorable
at [Source: java.io.StringReader#100edc0; line: 1, column: 16] (through reference chain: University["university"])
I know my JSON data is returning List of universities. But how to map those in List I am not aware of. Any sort of help will be greatly appreciated.

Answer 1

You can add parent class
public class UniversityList {
private List<University> university;
//... Getter and Setter Methods...
}
and us it like this:
ObjectMapper mapper = new ObjectMapper();
UniversityList list = mapper.readValue(json, UniversityList.class));
University university = list.getUniversity().get(0)
Other option is to create custom deserializer for your University class
Here is demo:
public static void main(String[] args) throws IOException {
ObjectMapper mapper = new ObjectMapper();
SimpleModule module = new SimpleModule();
module.addDeserializer(University.class, new UniversityDeserializer());
mapper.registerModule(module);
University university = mapper.readValue(json, University.class);
}
public static class UniversityDeserializer extends JsonDeserializer<University> {
private ObjectMapper unmodifiedMapper = new ObjectMapper();
#Override
public University deserialize(JsonParser p, DeserializationContext ctxt)
throws IOException{
JsonNode node = p.readValueAsTree();
JsonNode array = node.get("university");
if (array != null && array.isArray()){
JsonNode uniNode = array.get(0);
return unmodifiedMapper.treeToValue(uniNode, University.class);
}
return null;
}
}