How to modify the value of a JsonNode recursively using Jackson

Question

Requirements:
I want to apply some functions on the inner values of the JsonNode. The functions can be different eg:- lowercasing some values or appending something to the values or replace the values with something. How can I achieve that using Jackson library? Note that the structure of the JSON data can be different which means I want to build a generic system which will accept some path expression which will basically decide where to change. I want to use functional programming style, so that I can pass these functions as arguments.

eg:

input:

{
  "name": "xyz",
  "values": [
    {
      "id": "xyz1",
      "sal": "1234",
      "addresses": [
        {
          "id": "add1",
          "name": "ABCD",
          "dist": "123"
        },
        {
          "id": "add2",
          "name": "abcd3",
          "dist": "345"
        }
      ]
    },
    {
      "id": "xyz2",
      "sal": "3456",
      "addresses": [
        {
          "id": "add1",
          "name": "abcd",
          "dist": "123"
        },
        {
          "id": "add2",
          "name": "XXXXX",
          "dist": "345"
        }
      ]
    }
  ]
}

In this case I have to two functions basically, lowercase() and convert_to_number(). I want to apply lowercase() function on all the "name" attribute inside all the "addresses" of each "value". same goes for convert_to_number() , but for all the "dist" attribute.

So, basically the JSON expressions will be something like below for the functions:

lowercase() : /values/*/addresses/*/name
convert_to_number() : /values/*/addresses/*/dist

output:

{
  "name": "xyz",
  "values": [
    {
      "id": "xyz1",
      "sal": "1234",
      "addresses": [
        {
          "id": "add1",
          "name": "abcd",
          "dist": 123
        },
        {
          "id": "add2",
          "name": "abcd3",
          "dist": 345
        }
      ]
    },
    {
      "id": "xyz2",
      "sal": "3456",
      "addresses": [
        {
          "id": "add1",
          "name": "abcd",
          "dist": 123
        },
        {
          "id": "add2",
          "name": "xxxx",
          "dist": 345
        }
      ]
    }
  ]
}

Client code:

JsonNode jsonNode = ...
applyFunctionsRecursivelyBasedOnExpr(JsonNode jsonNode, String expr, Function )

Answer 1

As @MichalZiober in his answer already pointed out, JsonPath offers a much more powerful API than Jackson, when you need to do JSON-path-based operations.

Using methods JsonPath.parse and WriteContext.map you can solve your problem in just a few lines:

import java.io.File;
import com.jayway.jsonpath.Configuration;
import com.jayway.jsonpath.JsonPath;

public class Main {

    public static void main(String[] args) throws Exception {
        File file = new File("input.json");
        String json = JsonPath.parse(file)
                .map("$.values[*].addresses[*].name", Main::lowerCase)
                .map("$.values[*].addresses[*].dist", Main::convertToNumber)
                .jsonString();
        System.out.println(json);
    }

    private static Object lowerCase(Object currentValue, Configuration configuration) {
        if (currentValue instanceof String)
            return ((String)currentValue).toLowerCase();
        return currentValue;
    }

    private static Object convertToNumber(Object currentValue, Configuration configuration) {
        if (currentValue instanceof String)
            return Integer.valueOf((String)currentValue);
        return currentValue;
    }
}