CODEWITHSUNDEEP
javajsonjacksondeserializationjson-deserialization
deffy50
deffy50

Reputation: 93

Convert values from json string to object

I have a JSON payload of the format, with each value a list with single map element:

{
  "redundant_str_1": [
    {
      "attr_1": "val1",
      "attr_2": "val2"
    }
  ],
  "rendundant_str_2": [
    {
      "attr_1": "val4",
      "attr_2": "val3"
    }
  ]
}

Model is:

public class MyObj {

     private String attr_1;
     private String attr_2;
}

How can I map above response to List<MyObj> by neglecting the keys and taking only element from lists?

Upvotes: 1

Views: 98

Answers (3)

Michał Ziober
Michał Ziober

Reputation: 38655

Your response is of form Map<String, List<MyObj>>. You can deserialise it to given type and after this convert to a List<MyObj>.

import com.fasterxml.jackson.core.type.TypeReference;
import com.fasterxml.jackson.databind.ObjectMapper;
import com.fasterxml.jackson.databind.json.JsonMapper;
import lombok.Data;
import lombok.ToString;

import java.io.File;
import java.io.IOException;
import java.util.Collection;
import java.util.List;
import java.util.Map;
import java.util.stream.Collectors;

public class MyObjApp {
    public static void main(String[] args) throws IOException {
        File jsonFile = new File("./resource/test.json").getAbsoluteFile();

        ObjectMapper mapper = JsonMapper.builder().build();
        TypeReference<Map<String, List<MyObj>>> respType = new TypeReference<Map<String, List<MyObj>>>() {};
        Map<String, List<MyObj>> response = mapper.readValue(jsonFile, respType);

        List<MyObj> myObjs = response.values().stream().flatMap(Collection::stream).collect(Collectors.toList());
        System.out.println(myObjs);
    }
}

@Data
@ToString
class MyObj {

    private String attr_1;
    private String attr_2;
}

Above code prints:

[MyObj(attr_1=val1, attr_2=val2), MyObj(attr_1=val4, attr_2=val3)]

Upvotes: 0

Eugene Trofimov
Eugene Trofimov

Reputation: 178

You can use Jackson (add dependencies to jackson-core and jackson-databind):

  String json = "[" +
                "{\"attr_1\": \"val1\", \"attr_2\": \"val2\"}, " +
                "{\"attr_1\": \"val4\", \"attr_2\": \"val3\"}"
                + "]";

  ObjectMapper mapper = new ObjectMapper();
  mapper.setVisibility(PropertyAccessor.FIELD, JsonAutoDetect.Visibility.ANY);
  List<MyObj> list = Arrays.asList(mapper.readValue(json, MyObj[].class));

Or, if you add to MyObj setters on fields or make them public there will be no needed the row:

mapper.setVisibility(PropertyAccessor.FIELD, JsonAutoDetect.Visibility.ANY);

Upvotes: 0

Ankit Chauhan
Ankit Chauhan

Reputation: 704

String json = "{\"redundant_str_1\": [{\"attr_1\": \"val1\", \"attr_2\": \"val2\"}], \"rendundant_str_2\": [{\"attr_1\": \"val4\", \"attr_2\": \"val3\"}]}";
ObjectMapper objectMapper = new ObjectMapper();
List<MyObj> myObjList = new ArrayList<>();

ObjectNode objectNode = (ObjectNode) objectMapper.readTree(json);
    for (Iterator<JsonNode> it = objectNode.elements(); it.hasNext(); ) {
        ArrayNode arrayNode = (ArrayNode) it.next();
        MyObj myObj = objectMapper.treeToValue(arrayNode.get(0),MyObj.class);
        myObjList.add(myObj);
    }
System.out.println("List : " + myObjList);

Output :

   List : [MyObj{attr_1='val1', attr_2='val2'}, MyObj{attr_1='val4',attr_2='val3'}]

Upvotes: 1

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