Java simulates concurrent access

Class:NetUtils.java

import java.io.DataInputStream;      
import java.io.DataOutputStream;          
import java.net.HttpURLConnection;      
import java.net.URL;          
import java.util.Map; 
import java.util.Properties;
public class NetUtils
{
public static final String CHARACTER_ENCODING = "UTF-8";      
  public static final String PATH_SIGN = "/";      
  public static final String METHOD_POST = "POST";      
  public static final String METHOD_GET = "GET";      
  public static final String CONTENT_TYPE = "Content-Type";      
   
  /**    
   * 以POST方式向指定地址发送数据包请求,并取得返回的数据包    
   *     
   * @param urlString    
   * @param requestData    
   * @return 返回数据包    
   * @throws Exception    
   */     
  public static byte[] requestPost(String urlString, byte[] requestData)      
          throws Exception
  {      
      Properties requestProperties = new Properties();      
      requestProperties.setProperty(CONTENT_TYPE,      
              "application/octet-stream; charset=utf-8");      
   
      return requestPost(urlString, requestData, requestProperties);      
  }      
  /**    
   * 以POST方式向指定地址发送数据包请求,并取得返回的数据包    
   *     
   * @param urlString    
   * @param requestData    
   * @param requestProperties    
   * @return 返回数据包    
   * @throws Exception    
   */     
  public static byte[] requestPost(String urlString, byte[] requestData,      
          Properties requestProperties) throws Exception
  {
      byte[] responseData = null;      
      HttpURLConnection con = null;      
   
      try {      
          URL url = new URL(urlString);      
          con = (HttpURLConnection) url.openConnection();      
          //设置请求属性
          if ((requestProperties != null) && (requestProperties.size() > 0))
          {      
              for (Map.Entry<Object, Object> entry : requestProperties.entrySet())
              {      
                  String key = String.valueOf(entry.getKey());      
                  String value = String.valueOf(entry.getValue());      
                  con.setRequestProperty(key, value);      
              }      
          }      
   
          con.setRequestMethod(METHOD_POST); // 置为POST方法      
   
          con.setDoInput(true); // 开启输入流      
          con.setDoOutput(true); // 开启输出流      
   
          // 如果请求数据不为空，输出该数据。      
          if (requestData != null)
          {      
              DataOutputStream dos = new DataOutputStream(con.getOutputStream());      
              dos.write(requestData);
              dos.flush();      
              dos.close();      
          }      
   
          int length = con.getContentLength();      
          // 如果回复消息长度不为-1，读取该消息。      
          if (length != -1)
          {      
              DataInputStream dis = new DataInputStream(con.getInputStream());      
              responseData = new byte[length];      
              dis.readFully(responseData);      
              dis.close();      
          }      
      }
      catch (Exception e)
      {      
          throw e;      
      }
      finally
      {      
          if (con != null)
          {      
              con.disconnect();      
              con = null;      
          }      
      }      
      return responseData;      
  }      
}