HttpUrlConnection json POST 전송시 400 에러가 나는경우

package naverpay;
 
import java.io.BufferedReader;
import java.io.DataOutputStream;
import java.io.InputStream;
import java.io.InputStreamReader;
import java.io.OutputStream;
import java.io.UnsupportedEncodingException;
import java.net.URL;
import java.net.URLEncoder;
import java.security.cert.CertificateException;
import java.security.cert.X509Certificate;
import javax.net.ssl.HostnameVerifier;
import javax.net.ssl.HttpsURLConnection;
import javax.net.ssl.SSLContext;
import javax.net.ssl.SSLSession;
import javax.net.ssl.TrustManager;
 
import org.json.simple.JSONArray;
import org.json.simple.JSONObject;
 
 
public class HttpPost {
 
 public static void main(String[] args) {
     HttpPost obj = new HttpPost();
     obj.getHttpsConnection();
 }
 
 public JSONObject getMakeJsonData() {
     
   JSONObject object = new JSONObject();
   object.put("modelVersion", "2");   
   object.put("merchantUserKey", "");
   object.put("merchantPayKey", "");
   object.put("productName", "테스트상품");
   object.put("productCount", 1);
   object.put("totalPayAmount", 1000);   
   object.put("returnUrl", "http://localhost:8080/naverpay/");
   object.put("taxScopeAmount", 1000);
   object.put("taxExScopeAmount", 0);
   object.put("purchaserName", "구매자");   
  
   JSONArray list = new JSONArray();
   
   JSONObject productItem = new JSONObject();
   productItem.put("categoryType", "INSURANCE");
   productItem.put("categoryId", "TRAVELER");
   productItem.put("uid", "005");
   productItem.put("name", "테스트상품");
   productItem.put("payReferrer", "ETC");
   productItem.put("count", 1);
   
   list.add(productItem);
   object.put("productItems", list);
   
   return object;
 }
 
 public String UrlEncodeUTF8(String s) {
     try{
         return  URLEncoder.encode(s, "UTF-8");
     } catch(UnsupportedEncodingException ex) {
        throw new UnsupportedOperationException(ex); 
     }
 }
 
 public void getHttpsConnection() {
 
  HttpsURLConnection conn = null;
  try {
   URL url = new URL("https://dev.apis.naver.com/partner-id/naverpay/payments/v2/reserve");
   conn = (HttpsURLConnection) url.openConnection();
   conn.setRequestMethod("POST");
   conn.setRequestProperty("X-Naver-Client-Id", "");
   conn.setRequestProperty("X-Naver-Client-Secret", "");
   conn.setRequestProperty("Content-Type", "application/json");
   conn.setRequestProperty("charset", "UTF-8");
   conn.setDoOutput(true);
   conn.setUseCaches(false);
   conn.setConnectTimeout(10000);
   conn.setReadTimeout(10000);
   conn.setHostnameVerifier(new HostnameVerifier() {
 
    @Override
    public boolean verify(String hostname, SSLSession session) {
     return true;
    }
   });
   
   // SSL setting
   SSLContext context = SSLContext.getInstance("TLS");
   context.init(null, new TrustManager[]{
     new javax.net.ssl.X509TrustManager() {
      
      @Override
      public X509Certificate[] getAcceptedIssuers() {
       return null;
      }
      
      @Override
      public void checkServerTrusted(X509Certificate[] chain, String authType) throws CertificateException {
      }
      
      @Override
      public void checkClientTrusted(X509Certificate[] chain, String authType) throws CertificateException {
      }
     }
   }, null);
   conn.setSSLSocketFactory(context.getSocketFactory());
      
   // Connect to host 
   conn.connect(); 
   conn.setInstanceFollowRedirects(true); 
  
   String param = this.getMakeJsonData().toJSONString();
   
   OutputStream wr1 = conn.getOutputStream();
   DataOutputStream wr = new DataOutputStream(conn.getOutputStream());   
   
   wr1.write(param.getBytes("UTF-8"));
   wr1.flush();
   wr1.close();
 
 
   final int responseCode = conn.getResponseCode(); 
   InputStream in = conn.getInputStream(); 
   BufferedReader reader = new BufferedReader(new InputStreamReader(in));
   final StringBuffer buffer = new StringBuffer();
   String line = null; 
   while ((line = reader.readLine()) != null) { 
 
       buffer.append(line);
   } 
 
   reader.close();
   System.out.println("##########");
   System.out.println("##########");
   System.out.println("##########");
   System.out.println("##########");
   System.out.println("##########");
   System.out.println("result ::: "+buffer.toString());
 
  } catch (Exception e) {
   e.printStackTrace();
  } finally {
   if(conn != null) {
    conn.disconnect();
   }
  }
 
 }
 
}
 
 

네이버페이 결제예약호출 예제시 400에러가 발생하여 해당코드를 위와같이 수정하였다. 

json post 전송시 DataOutputStream 을 통해 전송하였으며 21라인에 UTF-8로 반드시 인코딩해서 데이터를 넘겨준다.