JSON object array to pojo

Question

When I invoke a REST service (GET) from postman, it retrieves the result. But when tried to consume the service from code, I dont' get the data as expected. I suspect it has something to do with the JSON/POJO mapping. I tried it different ways but does not give the result. What could be possibly wrong here?

Here is my json response when I try from postman

[
  {
    "id": 20,
    "type": 2,
    "data": {
      "name": "car"
    }
  },
  {
   "id": 20,
   "type": 2,
   "data": {
    "name": "car"
    }
  }
]

Here is my pojo:

class Market{
  public int id;
  public int type;
  public MarketData data;
}
class MarketData {
   public Strig name;

}

And here is how I consume the service:

HttpClient client = HttpClients.custom().build();

 HttpUriRequest request = RequestBuilder.get()
         .setUri("url")
         .setHeader(HttpHeaders.CONTENT_TYPE, "application/json")
         .setHeader(HttpHeaders.ACCEPT, "application/json")
         .build();

 HttpResponse response = client.execute(request);
 if (response.getStatusLine().getStatusCode() != 200) {
     throw new RuntimeException("Failed : HTTP error code : "
             + response.getStatusLine().getStatusCode());
 } 
 
 ObjectMapper mapper = new ObjectMapper();
 MarketData[] marketData = mapper.readValue(response.getEntity().getContent(), MarketData[].class);
 

Answer 1

As pointed out in comment by Nico, I think you have a typo on the objectMapper.readValue() line. It should be providing array type for Market, not MarketData. What I mean is this line:

MarketData[] marketData = mapper.readValue(response.getEntity().getContent(), MarketData[].class);

Should actually be:

Market[] markets = objectMapper.readValue(response, Market[].class);

I tested this code like this:

File responseFile = new File(JsonObjectArrayToPojo.class.getResource("/response.json").getFile());
String response = new String(Files.readAllBytes(responseFile.toPath()));
ObjectMapper objectMapper = new ObjectMapper();
Market[] markets = objectMapper.readValue(response, Market[].class);

System.out.println("marketData length " + markets.length);
for (Market m :  markets) {
    System.out.printf("\tid: %s", m.id);
    System.out.printf("\ttype: %s", m.type);
    System.out.printf("\tdata name: %s", m.data.name);

    System.out.println();
}

I added this response.json to my resource directory:

[{
    "id": 20, "type": 2, "data": { "name": "car"}
  },
  {
    "id": 10, "type": 1, "data": { "name": "Bike" }
  }]

This prints the following output:

marketData length 2
    id: 20  type: 2 data name: car
    id: 10  type: 1 data name: Bike