When you try convert your Map into custom POJO class , objectMapper is giving error because in your map, some of the values are json strings and object mapper will not be able to convert it directly. You may have to check for Json pattern satisfying values within your map and explicity convert them to objects before going for Map to POJO conversion.

You can try something similar to this for those map values which are json strings and then do your conversion:

newMap.put(entry.getKey(), objectMapper.readValue(mapValue, Object.class);