Parsing JSON maps / dictionaries with Gson?

Question

I need to parse a JSON Response that looks like:

{"key1": "value1", 
 "key2": "value2", 
 "key3": 
    {"childKey1": "childValue1", 
     "childKey2": "childValue2", 
     "childKey3": "childValue3" }
}

class Egg { 
    @SerializedName("key1")
    private String mKey1;

    @SerializedName("key2")
    private String mKey2;

    @SerializedName("key3")
    // ???
}

I'm reading through the Gson docs but cannot figure out how to properly deserialize a dictionary to a Map.

Answer 1

Gson readily handles deserialization of a JSON object with name:value pairs into a Java Map.

Following is such an example using the JSON from the original question. (This example also demonstrates using a FieldNamingStrategy to avoid specifying the serialized name for every field, provided that the field-to-element name mapping is consistent.)

import java.io.FileReader;
import java.lang.reflect.Field;
import java.util.Map;

import com.google.gson.FieldNamingStrategy;
import com.google.gson.Gson;
import com.google.gson.GsonBuilder;

public class Foo
{
  public static void main(String[] args) throws Exception
  {
    GsonBuilder gsonBuilder = new GsonBuilder();
    gsonBuilder.setFieldNamingStrategy(new MyFieldNamingStrategy());
    Gson gson = gsonBuilder.create();
    Egg egg = gson.fromJson(new FileReader("input.json"), Egg.class);
    System.out.println(gson.toJson(egg));
  }
}

class Egg
{
  private String mKey1;
  private String mKey2;
  private Map<String, String> mKey3;
}

class MyFieldNamingStrategy implements FieldNamingStrategy
{
  //Translates the Java field name into its JSON element name representation.
  @Override
  public String translateName(Field field)
  {
    String name = field.getName();
    char newFirstChar = Character.toLowerCase(name.charAt(1));
    return newFirstChar + name.substring(2);
  }
}

Answer 2

As far as I remember you should create separate class for each json object. Try something like this:

class Key { 
    @SerializedName("childKey1")
    private String mchildKey1;

    @SerializedName("childKey2")
    private String mchildKey2;

    @SerializedName("childKey3")
    private String mchildKey3;
}

class Egg { 
    @SerializedName("key1")
    private String mKey1;

    @SerializedName("key2")
    private String mKey2;

    @SerializedName("key3")
    private Key mKey3;
}

If this is not what you expected you can write your own serialize/deserialize adapter.