Example of deserializing JSON (using GSON) to various object types based on a type embedded in the JSON object.

GsonTestClass.java

public class GsonTestClass {
	static Gson gson = new Gson();

	/* Running the main method will produce the following output:
	 *
	 * Before Serializing/Deserializing:	{"foo1":"fooooo","bar1":"barrrr","type":"POJO1"}
	 * Before Serializing/Deserializing:	{"foo2":"fooooooooooo","bar2":["bar","barr"],"type":"POJO2"}
	 * After Serialization (Knowing Type):	{"foo1":"fooooo","bar1":"barrrr","type":"POJO1"}
	 * After Serialization (Knowing Type):	{"foo2":"fooooooooooo","bar2":["bar","barr"],"type":"POJO2"}
	 * After Serialization (Type Unknown):	{"foo1":"fooooo","bar1":"barrrr","type":"POJO1"}
	 * After Serialization (Type Unknown):	{"foo2":"fooooooooooo","bar2":["bar","barr"],"type":"POJO2"}
	 */
	public static void main(String[] args) {

		Pojo1 one = new Pojo1();
		Pojo2 two = new Pojo2();
		System.out.println("Before Serializing/Deserializing:\t" + one);
		System.out.println("Before Serializing/Deserializing:\t" + two);
		
		String json1 = gson.toJson(one);
		String json2 = gson.toJson(two);
		
		// Knowing type beforehand.
		Pojo1 oneAfter = gson.fromJson(json1, Pojo1.class);
		Pojo2 twoAfter = gson.fromJson(json2, Pojo2.class);
		System.out.println("After Serialization (Knowing Type):\t" + oneAfter);
		System.out.println("After Serialization (Knowing Type):\t" + twoAfter);
		
		// Without knowing type (get type using JsonParser).
		JsonParser parser = new JsonParser();
		PojoType type1 = PojoType.valueOf(parser.parse(json1).getAsJsonObject().getAsJsonPrimitive("type").getAsString());
		PojoType type2 = PojoType.valueOf(parser.parse(json2).getAsJsonObject().getAsJsonPrimitive("type").getAsString());
		JsonPojo oneAfterAbstract = gson.fromJson(json1, type1.typeClass);
		JsonPojo twoAfterAbstract = gson.fromJson(json2, type2.typeClass);
		System.out.println("After Serialization (Type Unknown):\t" + oneAfterAbstract);
		System.out.println("After Serialization (Type Unknown):\t" + twoAfterAbstract);
	}
	
	static abstract class JsonPojo {
		PojoType type;
		@Override
		public String toString() {
			return gson.toJson(this); // Using Gson for easy toString().
		}
	}
	
	static class Pojo1 extends JsonPojo {
		String foo1 = "fooooo";
		String bar1 = "barrrr";
		public Pojo1() {
			type = PojoType.POJO1;
		}
	}
	
	static class Pojo2 extends JsonPojo {
		String foo2 = "fooooooooooo";
		List<String> bar2 = Arrays.asList("bar", "barr"); 
		public Pojo2() {
			type = PojoType.POJO2;
		}
	}
	
	static enum PojoType {
		POJO1(Pojo1.class),
		POJO2(Pojo2.class),
		;
		Class<? extends JsonPojo> typeClass;
		private PojoType(Class<? extends JsonPojo> typeClass) {
			this.typeClass = typeClass;
		}
	}
}