JSON Structural Transformation: Key and Value Swapping Between Objects

A common requirement when integrating systems is to reshape JSON payloads—renaming keys, copying values, or populating fields with dynamic data such as timestamps. A mapping‑based approach can handle these transformations declaratively. This article demonstrates how to swap keys and values between two JSON object structures using a Java utility.

Transformation Mapping Configuration

The core of the transformation is a list of mapping rules. Each rule specifies:

• target path – the location in the destination JSON wheree the result will be placed.
• source path – the location in the source JSON from which data is retrieved.
• transform type – the operation to perform:
  • 1 : copy source key → target key
  • 2 : copy source key → target value
  • 3 : copy source value → target key
  • 4 : copy source value → target value
• options – additional flags to array handling, key generation, and mapping strategy.

A mapping rule is represented as a simple object:

{
    "targetPath": "root.dev_aim",
    "sourcePath": "root.dev_org",
    "type": 1
}

Example: Swapping Keys and Values

Given the following source and a target template:

Source JSON:

{
    "dev_org": {
        "642fccd1_org": {
            "1_org": "111_org",
            "2_org": "222_org"
        }
    },
    "time_org": 1682471111
}

Target Template (provides the desired key structure):

{
    "dev_aim": {
        "642fccd1_aim": {
            "1_aim": "111_aim",
            "2_aim": "222_aim"
        }
    },
    "time_aim": 1682472222
}

The goal is to transform the source so that:

• keys dev_org, 642fccd1_org, 1_org, 2_org, and time_org are renamed to their _aim counterparts.
• values under 1_org, 2_org are preserved.
• the time_aim field is filled with the current UTC timestamp instead of the original number.

Java Implementation

The transformation engine accepts a source string, a target template, and a list of rules. The following code sets up the required mappings and executes the conversion:

import com.fasterxml.jackson.databind.ObjectMapper;
import java.util.ArrayList;
import java.util.List;

public class JsonKeyValueSwap {
    public static void main(String[] args) {
        ObjectMapper mapper = new ObjectMapper();
        String sourceJson = "{\"dev_org\":{\"642fccd1_org\":{\"1_org\":\"111_org\",\"2_org\":\"222_org\"}},\"time_org\":1682471111}";
        String targetTemplate = "{\"dev_aim\":{\"642fccd1_aim\":{\"1_aim\":\"111_aim\",\"2_aim\":\"222_aim\"}},\"time_aim\":1682472222}";

        List<TransformationRule> rules = new ArrayList<>();
        // Rename top-level key
        rules.add(new TransformationRule("root.dev_aim", "root.dev_org", 1));
        // Rename nested object key
        rules.add(new TransformationRule("root.dev_aim.642fccd1_aim", "root.dev_org.642fccd1_org", 1));
        // First inner key and value
        rules.add(new TransformationRule("root.dev_aim.642fccd1_aim.1_aim", "root.dev_org.642fccd1_org.1_org", 1));
        rules.add(new TransformationRule("root.dev_aim.642fccd1_aim.1_aim", "root.dev_org.642fccd1_org.1_org", 4));
        // Second inner key (treat source value as target key)
        rules.add(new TransformationRule("root.dev_aim.642fccd1_aim.2_aim", "root.dev_org.642fccd1_org.2_org", 3));
        rules.add(new TransformationRule("root.dev_aim.642fccd1_aim.2_aim", "root.dev_org.642fccd1_org.2_org", 4));
        // Time key
        rules.add(new TransformationRule("root.time_aim", "root.time_org", 1));
        // Replace value with current time (using a built‑in placeholder)
        rules.add(new TransformationRule("root.time_aim", "#Time#", 4));

        JsonTransformer transformer = new JsonTransformer(sourceJson, targetTemplate, rules);
        String result = transformer.transform();
        System.out.println("Transformed JSON:\n" + result);
    }
}

The TransformationRule class encapsulates target path, source path, and type, while JsonTransformer processes the rules. The special placeholder #Time# injects the current UTC timestamp when used as a source value with type 4.

Expected output (keys match the target template, values come from the source, and time is replaced by a current ISO‑8601 string):

{
    "dev_aim": {
        "642fccd1_aim": {
            "1_aim": "111_org",
            "2_aim": "222_org"
        }
    },
    "time_aim": "2024-03-21T07:28:54.893Z"
}

By composing rules of different types, you can remodel almost any JSON structure without writing custom procedural code.