SMTPConnection.java

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

/**
 * Open an SMTP connection to a mailserver and send one mail.
 *
 */
public class SMTPConnection {
  /* The socket to the server */
  private Socket connection;

  /* Streams for reading and writing the socket */
  private BufferedReader fromServer;
  private DataOutputStream toServer;

  private static final int SMTP_PORT = 25;
  private static final String CRLF = "\r\n";

  /* Are we connected? Used in close() to determine what to do. */
  private boolean isConnected = false;

  /* Create an SMTPConnection object. Create the socket and the
   *  associated streams. Initialize SMTP connection. */
  public SMTPConnection(Envelope envelope) throws IOException {
    connection = new Socket(envelope.DestHost, SMTP_PORT);
    fromServer = new BufferedReader(new InputStreamReader(connection.getInputStream()));
    toServer = new DataOutputStream(connection.getOutputStream());

    /* Read a line from server and check that the reply code is 220.
       If not, throw an IOException */
    String reply = fromServer.readLine();
    if(parseReply(reply) != 220) {
      System.out.println("Not 220");
      throw new IOException();
    }

    /* SMTP handshake. We need the name of the local machine.
       Send the appropriate SMTP handshake command. */
    String localhost = (InetAddress.getLocalHost()).getCanonicalHostName();
    sendCommand("HELO "  + localhost, 250);
    isConnected = true;
  }

  /* Send the message. Write the correct SMTP-commands in the
     correct order. No checking for errors, just throw them to the
     caller. */
  public void send(Envelope envelope) throws IOException
  {
    sendCommand("MAIL From: " + envelope.Sender, 250);
    sendCommand("RCPT To: " + envelope.Recipient, 250);
    sendCommand("DATA", 354);
    sendCommand(envelope.Message.toString() + CRLF + ".", 250);
  }

  /* Close the connection. First, terminate on SMTP level, then
     close the socket. */
  public void close() {
    isConnected = false;
    try {
      sendCommand("QUIT", 221);
      connection.close();
    } catch (IOException e) {
      System.out.println("Unable to close connection: " + e);
      isConnected = true;
    }
  }

  /* Send an SMTP command to the server. Check that the reply code
     is what is is supposed to be according to RFC 821. */
  private void sendCommand(String command, int rc) throws IOException{

    /* Write command to server and read reply from server. */
    toServer.writeBytes(command + CRLF);
    /* Check that the server’s reply code is the same as the
       parameter rc. If not, throw an IOException. */
    String reply = fromServer.readLine();
    if (parseReply(reply) != rc) {
      System.out.println("Reply codes don't match");
      throw new IOException();
    }
  }

  /* Parse the reply line from the server. Returns the reply code. */
  private int parseReply(String reply) {
    String replyLine = reply.substring(0,3); //take first three digits of string
    int replyCode = Integer.parseInt(replyLine);
    return replyCode;
  }

  /* Destructor. Closes the connection if something bad happens. */
  protected void finalize() throws Throwable {
    if(isConnected) {
      close();
    }
    super.finalize();
  }
}