#2. Socket Prgrmming | MailClient Source Code.

//SMTPConnection.java

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

/**  * Open an SMTP connection to a remote machine and send one mail.  */
/*MY INFO  */
/**
 * @author Alek amodi@clunet.edu
 *
 *         Using Cal Lutheran Local Mailserver and port number this app can send
 *         and process SMT Protocol.
 *
 *         To: Dr. Chu
 */

/*
 * Developed on - Sep 08, 2011
 *
 * WireShark Lab work - MailClient
 */

public class SMTPConnection {
/* The socket to the server */
public Socket connection;
/* Streams for reading and writing the socket */
public BufferedReader fromServer;
public DataOutputStream toServer;
private static final int SMTP_PORT = 587;
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. Send HELO-command and check for errors.
*/
public SMTPConnection(Envelope envelope) throws IOException {
connection = new Socket(envelope.DestAddr, SMTP_PORT);
fromServer = new BufferedReader(new InputStreamReader(
connection.getInputStream()));
toServer = new DataOutputStream(connection.getOutputStream());
String reply = fromServer.readLine();
if (parseReply(reply) != 220) {
System.out.println("Error in connect.");
System.out.println(reply);
return;
}
String localhost = (InetAddress.getLocalHost()).getHostName();
try {
sendCommand("HELO " + localhost, 250);
} catch (IOException e) {
System.out.println("HELO failed. Aborting.");
return;
}
isConnected = true;
}

/*
* Send the message. Simply writes 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 {
String reply = null;
toServer.writeBytes(command + CRLF);
reply = fromServer.readLine();
if (parseReply(reply) != rc) {
System.out.println("Error in command: " + command);
System.out.println(reply);
throw new IOException();
}
}

/* Parse the reply line from the server. Returns the reply code. */
private int parseReply(String reply) {
StringTokenizer parser = new StringTokenizer(reply);
String replycode = parser.nextToken();
return (new Integer(replycode)).intValue();
}

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