Send simple message via SMTP as "ping"

MailPing.java

import java.io.*;
import java.net.*;
import java.util.*;

/**
 * MailPing is used to test communication with a mail server.
 *
 * @author  Thornton Rose
 * @version 1.1
 */
public class MailPing
{
   private static final int  SMTP_PORT = 25;
   private static final char SMTP_ERROR_CODE1 = '4';
   private static final char SMTP_ERROR_CODE2 = '5';

   public static void main(String[] args) {
      String host = null;
      String recipient = null;
      String sender = null;
      
      // Check args.

      if (args.length < 1) {
         System.out.println("MailPing");
         System.out.println("");
         System.out.println("Version 1.1");
         System.out.println("by Thornton Rose");
         System.out.println("");
         System.out.println("This program is used to test communication with a mail server using SMTP. If");
         System.out.println("only host is specified, only the socket connection is tested. If recipient is");
         System.out.println("specified, a test message is sent to recipient. If sender is not specified,");
         System.out.println("sender = recipient.");
         System.out.println("");
         System.out.println("");
         System.out.println("Usage:");
         System.out.println("   MailPing host [recipient] [sender]");
         System.out.println("");
         System.out.println("Parameters:");
         System.out.println("   host      = Name or IP address of mail host.");
         System.out.println("   recipient = E-mail address of recipient.");
         System.out.println("   sender    = E-mail address of sender.");
      }
      else {
         // Get host.

         host = args[0];

         // Get recipient and sender.

         if (args.length >= 2) {
            recipient = args[1];
         }

         if (args.length >= 3) {
            sender = args[2];
         }

         if (sender == null) {
            sender = recipient;
         }

         // Ping that server!
         
         (new MailPing()).ping(host, recipient, sender);
      }

      System.exit(0);
   }

   /** ping() attempts to communicate with the specified host. All
    * I/O for the session is printed to stdout. If recipient is not
    * <i>null</i>, a test message is sent to the recipient.
    *
    * @param host      The name or IP of the mail host (server).
    * @param recipient The e-mail address of the recipient.
    * @param sender    The e-mail address of the sender.
    */
   public void ping(String host, String recipient, String sender) {
      Socket            mailSocket;
      BufferedReader    socketInput;
      DataOutputStream  socketOutput;
      String            mailData;
      String            domain;

      try {
         // Open the connection to the host.

         mailSocket = new Socket(host, SMTP_PORT);

         try {
            // Get references to the input and output streams.

            socketInput = new BufferedReader(
               new InputStreamReader(mailSocket.getInputStream()) );
            socketOutput = new DataOutputStream(mailSocket.getOutputStream());

            // Get the initial reply from the server.

            readReply(socketInput);

            // If a recipient is specified, send a test message.

            if (recipient != null) {
               domain = "unknown.com";
               mailData =
                  "Date: " + (new Date()).toString() + "\r\n" +
                  "From: " + sender + "\r\n" +
                  "To: " + recipient + "\r\n" +
                  "Subject: Test message\r\n" +
                  "\r\n" +
                  "This is a test message from MailPing.\r\n";
         
               // Greet the server.

               sendCommand(socketOutput, "HELO " + domain);
               readReply(socketInput);

               // Send the sender's address.
   
               sendCommand(socketOutput, "MAIL FROM: " + sender);
               readReply(socketInput);

               // Send the recipient's address.

               sendCommand(socketOutput, "RCPT TO: " + recipient);
               readReply(socketInput);

               // Start the data section.

               sendCommand(socketOutput, "DATA");
               readReply(socketInput);

               // Send the mail message.
      
               sendCommand(socketOutput, mailData + ".");
               readReply(socketInput);

               // End the session.
      
               sendCommand(socketOutput, "QUIT");
               readReply(socketInput);
            }
         } finally {
            mailSocket.close();
         }
      }
      catch(Exception theException) {
         System.out.println(theException);
      }
   }

   /**
    * sendCommand() sends an SMTP command to the SMTP server. An
    * SMTP command is a string that looks like:
    * <pre>
    * [key words] [data][CR][LF]
    * </pre>
    *
    * <p>Example: <pre>HELO xyz.com</pre>
    *
    * @param out          The output stream to which to write the command.
    * @param command      The command to write.
    *
    * @exception IOException No special handling is done; the exception is
    *    passed back up the call chain.
    */
   private void sendCommand(DataOutputStream out, String command) 
      throws IOException {
      
      out.writeBytes(command + "\r\n");
      System.out.println(command);
   }

   /**
    * readReply() reads the reply from the SMTP server.
    *
    * @param reader       The input reader from which to read the reply.
    *
    */
   /* @exception IOException If an IOException occurs because of an error
    *    with socket IO, no special handling is done, and the exception is
    *    passed back up the call chain. If the status code in the reply from
    *    the SMTP server is equal to SMTP_ERROR_CODE1 or SMTP_ERROR_CODE2, an
    *    IOException containing "SMTP: " + the reply is thrown.
    */
   private void readReply(BufferedReader reader)
      throws IOException {
      
      String reply;
      char   statusCode;
      
      reply = reader.readLine();
      statusCode = reply.charAt(0);
      System.out.println(reply);

      /*
      if ( (statusCode == SMTP_ERROR_CODE1) | 
           (statusCode == SMTP_ERROR_CODE2) ) {
         throw (new IOException("SMTP: " + reply));
      }
      */
   }
}