FlattenerTest

import com.fasterxml.jackson.databind.ObjectMapper;
import org.junit.Test;

import java.io.IOException;
import java.util.Map;

import static org.junit.Assert.*;

public class FlattenerTest {
    @Test
    public void testitShouldFlatten() throws IOException {
        String json = "{\"root\":{\"shallowValue\":0,\"deep\":{\"deepValue\":0,\"array\":[1,2,3]},\"array\":[4,5,6,7]}}";
        ObjectMapper mapper = new ObjectMapper();
        Map<String, Object> map = mapper.readValue(json, Map.class);
        Flattener.process(map);
        String result = mapper.writeValueAsString(map);
        assertEquals("{\"root_shallowValue\":0,\"root_deep_array_count\":3,\"root_array_count\":4,\"root_deep_deepValue\":0}", result);
    }
}

Unit Test for https://gist.github.com/pbatey/4113ca593c181c94bc9c9f98972abe56