I apologize, but I must inform you that there is no JsonMerge class in the Apache Commons IO library. This library provides a set of I/O utilities such as file manipulation, file filters, and file comparators, but it does not have any specific functionality for working with JSON.

If you are looking for a way to merge multiple JSON objects into a single JSON object in Java, you can use a third-party library such as Jackson. Here is an example using the Jackson library:

import com.fasterxml.jackson.databind.JsonNode;
import com.fasterxml.jackson.databind.ObjectMapper;
import com.fasterxml.jackson.databind.node.ObjectNode;

public class JsonMergeExample {
    public static void main(String[] args) throws IOException {
        String json1 = "{\"firstName\":\"John\",\"lastName\":\"Doe\"}";
        String json2 = "{\"age\":30,\"address\":{\"street\":\"Main St\",\"city\":\"New York\"}}";

        // Create an ObjectMapper instance
        ObjectMapper mapper = new ObjectMapper();

        // Parse the JSON strings to JsonNode objects
        JsonNode jsonNode1 = mapper.readTree(json1);
        JsonNode jsonNode2 = mapper.readTree(json2);

        // Merge the two JSON objects
        ((ObjectNode) jsonNode1).setAll((ObjectNode) jsonNode2);

        // Print the merged JSON object
        System.out.println(jsonNode1);
    }
}