Conversion between Java Map type and Json string

import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStream;
import java.io.InputStreamReader;
import java.io.Reader;
import java.io.UnsupportedEncodingException;
import java.util.HashMap;
import java.util.Map;
import java.util.Scanner;


import com.google.gson.Gson;
import com.google.gson.GsonBuilder;


public class ConvertUtils {
//	Gson gson = new GsonBuilder().enableComplexMapKeySerialization().create();
	static Gson gson = new Gson ();
	
// Convert JSON string to Map data type
  public static HashMap get_request_json_object(InputStream input_stream){
  	HashMap mapObj=null;
      try {
          BufferedReader  streamReader = new BufferedReader(new InputStreamReader(input_stream,"UTF-8"));  
          StringBuilder responseStrBuilder = new StringBuilder();  
          String inputStr;
          while ((inputStr = streamReader.readLine()) != null) responseStrBuilder.append(inputStr);
//          mapObj = JSONObject.parseObject(responseStrBuilder.toString(),Map.class);
          mapObj = gson.fromJson(responseStrBuilder.toString(), HashMap.class);
          
      } catch (Exception e) {
          e.printStackTrace ();
      }
      return mapObj;
  }
  
// Map data type converted to JSON string
  public static String build_request_json_object(Map mapObj) {
  	String json_string = null;
  	try {
  		json_string = gson.toJson(mapObj);
  	} catch (Exception e) {
  		e.printStackTrace ();
  	}
  	return json_string;
  }
}