How to unwrap single item array and extract value field into one simple field? - jackson

Question

I have a JSON document similar to the following:
{
"aaa": [
{
"value": "wewfewfew"
}
],
"bbb": [
{
"value": "wefwefw"
}
]
}
I need to deserialize this into something more clean such as:
public class MyEntity{
private String aaa;
private String bbb;
}
What's the best way to unwrap each array and extract the "value" field on deserialization? Just custom setters? Or is there a nicer way?

Answer 1

For completeness, if you use jackson, you can enable the deserialization feature UNWRAP_SINGLE_VALUE_ARRAYS.
To do that, you have to enable it for the ObjectMapper like so:
ObjectMapper objMapper = new ObjectMapper()
.enable(DeserializationFeature.UNWRAP_SINGLE_VALUE_ARRAYS);
With that, you can just read the class as you are being used to in Jackson.
For example, assuming the class Person:
public class Person {
private String name;
// assume getter, setter et al.
}
and a json personJson:
{
"name" : [
"John Doe"
]
}
We can deserialize it via:
ObjectMapper objMapper = new ObjectMapper()
.enable(DeserializationFeature.UNWRAP_SINGLE_VALUE_ARRAYS);
Person p = objMapper.readValue(personJson, Person.class);

Answer 2

Quick solution with Gson is to use a JsonDeserializer like this:
package stackoverflow.questions.q17853533;
import java.lang.reflect.Type;
import com.google.gson.*;
public class MyEntityDeserializer implements JsonDeserializer<MyEntity> {
public MyEntity deserialize(JsonElement json, Type typeOfT,
JsonDeserializationContext context) throws JsonParseException {
String aaa = json.getAsJsonObject().getAsJsonArray("aaa").get(0)
.getAsJsonObject().get("value").getAsString();
String bbb = json.getAsJsonObject().getAsJsonArray("bbb").get(0)
.getAsJsonObject().get("value").getAsString();
return new MyEntity(aaa, bbb);
}
}
and then use it when parsing:
package stackoverflow.questions.q17853533;
import com.google.gson.*;
public class Q17853533 {
public static void main(String[] arg) {
GsonBuilder builder = new GsonBuilder();
builder.registerTypeAdapter(MyEntity.class, new MyEntityDeserializer());
String testString = "{ \"aaa\": [{\"value\": \"wewfewfew\" } ], \"bbb\": [ {\"value\": \"wefwefw\" } ] }";
Gson gson = builder.create();
MyEntity entity= gson.fromJson(testString, MyEntity.class);
System.out.println(entity);
}
}