Extract nested attribute value from JSON String using Apex

Salesforce offers two main ways to extract values from a JSON string

1. JSON.deserialize() This approach requires you to have a wrapper class/other valid entity to deserialize the data to.
2. JSON.createParser(jsonString) This approach requires you to loop through a bunch of confusing parser.nextToken() calls

In this article I am introducing an easy to use utility to extract inner attribute values from any JSON string. This is leveraging JSON.createParser(). But once you have this utility, you don't have to go through the parser.nextToken() confusion.

Example of use

Say you need to extract organization id from the following nested json string

{
  "data": {
    "user": {
      "organization": {
        "id": "123"
      }
    }
  }
}

You can do this by simply passing the JSON string and the path of the parameter to the utility

Utils.extractAttributeFromJson('{"data":{"user":{"organization":{"id":"123"}}}}', 'data.user.organization.id');

Sample utility class

public with sharing class Utils {

    /**************************************************************************************
    * @Description  This method extract value of inner attributes in a JSON
    * @Param		String - JSON string
    * @Param		String - JSON attribute path
    * @Return       String - This sample assumes returned value is a string
    * @Example
    * Utils.extractAttributeFromJson('{"data":{"user":{"organization":{"id":"123"}}}}', 'data.user.organization.id');
    **************************************************************************************/
    public static String extractAttributeFromJson(String jsonResponse, String attrString) {
        if(String.isBlank(jsonResponse) || String.isBlank(attrString)) return null;
        List<String> attrPath = attrString.split('\\.');
        JSONParser parser = JSON.createParser(jsonResponse);
        Integer index = 0;
        parser.nextToken();
        while(parser.nextToken() != null) {
            if (parser.getCurrentToken() == JSONToken.FIELD_NAME) {
                if(attrPath[index] == parser.getText()) {
                    if(index == attrPath.size()-1) {
                        parser.nextToken();
                        return parser.getText();
                    }else if(parser.nextToken() == JSONToken.START_OBJECT) {
                        index++;
                    }
                }
            }else if(parser.getCurrentToken() == JSONToken.START_OBJECT || parser.getCurrentToken() == JSONToken.START_ARRAY) {
                parser.skipChildren();
            }
        }
        return null;
    }
}

Please note that it will be more performant to use JSON.createParser() directly if you have multiple attributes to extract from the JSON.

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