public class SMSGenerator {
   public static HttpURLConnection sendSingleSMS(HttpURLConnection lconnection, String username,
       String password, String senderId,
       String mobileNo, String message) {
   try {
       String smsservicetype = "singlemsg"; // For single message.
       String query = "username=" + URLEncoder.encode(username)
               + "&password=" + URLEncoder.encode(password)
               + "&smsservicetype=" + URLEncoder.encode(smsservicetype)
               + "&content=" + URLEncoder.encode(message) + "&mobileno="
               + URLEncoder.encode(mobileNo) + "&senderid="
               + URLEncoder.encode(senderId);

       lconnection.setRequestProperty("Content-length", String.valueOf(query.length()));
       lconnection.setRequestProperty("Content-Type",
               "application/x-www-form-urlencoded");
       lconnection.setRequestProperty("User-Agent",
               "Mozilla/4.0 (compatible; MSIE 5.0; Windows 98; DigExt)");

       // open up the output stream of the connection
       DataOutputStream output = new DataOutputStream(lconnection.getOutputStream());

       // write out the data
       int queryLength = query.length();
       output.writeBytes(query);
       // output.close();

       // get ready to read the response from the cgi script
       DataInputStream input = new DataInputStream(lconnection.getInputStream());

       // read in each character until end-of-stream is detected
       for (int c = input.read(); c != -1; c = input.read()) {
           System.out.print((char) c);
       }
       input.close();
   } catch (Exception e) {
       System.out.println("Something bad just happened.");
       e.printStackTrace();
   }
   return lconnection;
}
public static boolean sendSMS(String mobilenumber, String msg) throws MalformedURLException, IOException {
   boolean flag = false;
   Proxy proxy = new Proxy(Proxy.Type.HTTP, new InetSocketAddress("xxxxxxxxxx", xx));
   URL surl = new URL("xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx");
   HttpURLConnection connection = null;
   connection = (HttpURLConnection) surl.openConnection(proxy);
   connection.setDoInput(true);
   connection.setDoOutput(true);
   connection.setRequestMethod("POST");
   HttpURLConnection.setFollowRedirects(true);
   System.out.println("Response code " + connection.getResponseMessage());
   System.out.println("code : " + connection.getResponseCode() + " " + HttpURLConnection.HTTP_NOT_FOUND);
   if ("OK".equals(connection.getResponseMessage())) {
       System.out.println("in");
       SMSGenerator.sendSingleSMS(connection, "username", "password", "SMS", mobilenumber, msg);
//             System.out.println("Sent successful SMS");
       flag = true;

   } else if (connection.getResponseCode() == HttpURLConnection.HTTP_OK) {
       System.out.println("Hiiii");
   } else if (connection.getResponseCode() == HttpURLConnection.HTTP_BAD_GATEWAY) {
       System.out.println("Hi 1");
   } else if (connection.getResponseCode() == HttpURLConnection.HTTP_INTERNAL_ERROR) {
       System.out.println("Hi 2");
   }
//        System.out.println("");
   return flag;
}
public static void main(String[] args) throws IOException {
   new SMSGenerator().sendSMS("xxxxxxxxxx", "ManojYest1");
}
}

java.lang.IllegalStateException: Already connected
   at sun.net.www.protocol.http.HttpURLConnection.setRequestProperty(HttpURLConnection.java:3013)