How to deserialize JSON into flat, Map-like structure?

Question

Have in mind that the JSON structure is not known before hand i.e. it is completely arbitrary, we only know that it is JSON format.

For example,

The followin

Answer 1

You can do this to traverse the tree and keep track of how deep you are to figure out dot notation property names:

import com.fasterxml.jackson.databind.JsonNode;
import com.fasterxml.jackson.databind.ObjectMapper;
import com.fasterxml.jackson.databind.node.ArrayNode;
import com.fasterxml.jackson.databind.node.ObjectNode;
import com.fasterxml.jackson.databind.node.ValueNode;
import java.io.IOException;
import java.util.HashMap;
import java.util.Iterator;
import java.util.Map;
import org.junit.Test;

public class FlattenJson {
  String json = "{\n" +
      "   \"Port\":\n" +
      "   {\n" +
      "       \"@alias\": \"defaultHttp\",\n" +
      "       \"Enabled\": \"true\",\n" +
      "       \"Number\": \"10092\",\n" +
      "       \"Protocol\": \"http\",\n" +
      "       \"KeepAliveTimeout\": \"20000\",\n" +
      "       \"ThreadPool\":\n" +
      "       {\n" +
      "           \"@enabled\": \"false\",\n" +
      "           \"Max\": \"150\",\n" +
      "           \"ThreadPriority\": \"5\"\n" +
      "       },\n" +
      "       \"ExtendedProperties\":\n" +
      "       {\n" +
      "           \"Property\":\n" +
      "           [                         \n" +
      "               {\n" +
      "                   \"@name\": \"connectionTimeout\",\n" +
      "                   \"$\": \"20000\"\n" +
      "               }\n" +
      "           ]\n" +
      "       }\n" +
      "   }\n" +
      "}";

  @Test
  public void testCreatingKeyValues() {
    Map map = new HashMap();
    try {
      addKeys("", new ObjectMapper().readTree(json), map);
    } catch (IOException e) {
      e.printStackTrace();
    }
    System.out.println(map);
  }

  private void addKeys(String currentPath, JsonNode jsonNode, Map map) {
    if (jsonNode.isObject()) {
      ObjectNode objectNode = (ObjectNode) jsonNode;
      Iterator> iter = objectNode.fields();
      String pathPrefix = currentPath.isEmpty() ? "" : currentPath + ".";

      while (iter.hasNext()) {
        Map.Entry entry = iter.next();
        addKeys(pathPrefix + entry.getKey(), entry.getValue(), map);
      }
    } else if (jsonNode.isArray()) {
      ArrayNode arrayNode = (ArrayNode) jsonNode;
      for (int i = 0; i < arrayNode.size(); i++) {
        addKeys(currentPath + "[" + i + "]", arrayNode.get(i), map);
      }
    } else if (jsonNode.isValueNode()) {
      ValueNode valueNode = (ValueNode) jsonNode;
      map.put(currentPath, valueNode.asText());
    }
  }
}

It produces the following map:

Port.ThreadPool.Max=150, 
Port.ThreadPool.@enabled=false, 
Port.Number=10092, 
Port.ExtendedProperties.Property[0].@name=connectionTimeout, 
Port.ThreadPool.ThreadPriority=5, 
Port.Protocol=http, 
Port.KeepAliveTimeout=20000, 
Port.ExtendedProperties.Property[0].$=20000, 
Port.@alias=defaultHttp, 
Port.Enabled=true

It should be easy enough to strip out @ and $ in the property names, although you could end up with collisions in key names since you said the JSON was arbitrary.