How to deserialize a Map<String, Object> into POJO?

Question

I have a Map<String, Object> which contains a deserialized form of JSON. I would like to deserialize this into the fields of a POJO.

I can perform this using Gson by serializing the Map into a JSON string and then deserializing the JSON string into the POJO, but this is inefficient (see example below). How can I perform this without the middle step?

The solution should preferably use either Gson or Jackson, as they're already in use by the project.

Example code:

import java.util.HashMap; import java.util.Map;  import com.google.gson.Gson;  public class Test {     public static void main(String[] args) {         Map<String, Object> innermap = new HashMap<String, Object>();         innermap.put("number", 234);         innermap.put("string", "bar");         Map<String, Object> map = new HashMap<String, Object>();         map.put("number", 123);         map.put("string", "foo");         map.put("pojo2", innermap);          Gson gson = new Gson();          // How to perform this without JSON serialization?         String json = gson.toJson(map);         MyPojo pojo = gson.fromJson(json, MyPojo.class);          System.out.println(pojo);     } }   class MyPojo {     private int number;     private String string;     private MyPojo pojo2;      @Override     public String toString() {         return "MyPojo[number=" + number + ", string=" + string + ", pojo2=" + pojo2 + "]";     } } 

Answer 1

Using Gson, you can turn your Map into a JsonElement, which you can then parse in exactly the same way using fromJson:

JsonElement jsonElement = gson.toJsonTree(map); MyPojo pojo = gson.fromJson(jsonElement, MyPojo.class); 

This is similar to the toJson method that you are already using, except that it avoids writing the JSON String representation and then parsing that JSON String back into a JsonElement before converting it to your class.

Answer 2

In Jackson you can use convertValue method. See below example:

mapper.convertValue(map, MyPojo.class);