SMTP Server

SMTPClient.java

import java.io.*;
import java.net.*;
public class SMTPClient
{
private boolean run=true;
public static void main(String[] args)
{
try
{
new SMTPClient().connect();
}
catch(Exception e)
{
}
}
public void connect() throws Exception
{
Socket s=new Socket("localhost",4000);
PrintWriter pw=new PrintWriter(s.getOutputStream(),true);
BufferedReader br=new BufferedReader(new InputStreamReader(s.getInputStream()));
BufferedReader bf=new BufferedReader(new InputStreamReader(System.in));
new Thread(new Runnable()
{
public void run()
{
while(run)
{
try
{
String msg=br.readLine();
if(msg!=null)
System.out.println(msg);
else run=false;
}
catch(Exception e)
{
}
}
}
}).start();
String id;
boolean val;
do
{
id=bf.readLine();
String emailreg="^[_A-Za-z0-9-]+(\\.[_A-Za-z0-9-]+)*@[_A-Za-z0-9-]+(\\.[_A-Za-z0-9-]+)*(\\.[_A-Za-z]{2,})$";
val=id.matches(emailreg);
if(!val)System.out.println("Wrong format email-id.please re-enter.");
}
while(!val);
pw.println(id);
System.out.println("Always input \n1-Send Mail\n2-Read mail\n3-Logout");
while(true)
{
int n=Integer.parseInt(bf.readLine());
pw.println(n);
switch(n)
{
case 1:System.out.println("Send To:");
	pw.println(bf.readLine());
	System.out.println("Message:");
	pw.println(bf.readLine()); 
	break;
case 2:run=false;
System.exit(0);
break;
}
}
}
}

SMTPServer.java

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

public class SMTPServer
{
	private ArrayList<user>users=new ArrayList<user>();
	public static void main(String[] args)
	{
		try
		{
			new SMTPServer().start();
		}
		catch(Exception e)
		{
		}
	}

	public void start() throws Exception
	{
		ServerSocket ss=new ServerSocket(4000);
		Socket s;
		while(true)
		{
			s=ss.accept();
			System.out.println("Client connected..");
			new Thread(new SocketHandler(s)).start();
		}
	}

	public boolean registerId(String id,SocketHandler sh)
	{
		user n;
		int i;
		for(i=0;i<users.size();i++)
		{
			n=users.get(i);

			if(n.id.equals(id))
			{
				if(n.sh!=null)
					return false;
				n.sh=sh;
				return true;
			}
		}
		user u=new user();
		u.id=id;
		u.sh=sh;
		users.add(u);
		return true;
	}

	public void sendMessage(String id,String to,String mbody)
	{
		message msg=new message();
		msg.from=id;
		msg.message=mbody;
		user n;
		for(int i=0;i<users.size();i++)
		{	
			n=users.get(i);
			if(n.id.equals(to))
				n.msgs.add(msg);
		}
		user u=new user();
		u.id=to;
		u.msgs.add(msg);
		users.add(u);
	}

	public ArrayList<message>getMessages(String id)
	{
		for(int i=0;i<users.size();i++)
		{
			user n=users.get(i);
			if(n.id.equals(id))
				return n.msgs;
		}
		return null;
	}

	public void logout(String id)
	{
		for(int i=0;i<users.size();i++)
		{
			user n=users.get(i);
			if(n.id.equals(id))
				n.sh=null;
		}
	}

	class user
	{
		String id;
		ArrayList<message>msgs=new ArrayList<message>();
		SocketHandler sh;
	}

	class message
	{
		String from;
		String message;
	}

	class SocketHandler implements Runnable
	{
		public Socket s;
		private String id;
		public SocketHandler(Socket s)
		{
			this.s=s;
		}
		public void run()
		{
			try
			{
				PrintWriter pw=new PrintWriter(s.getOutputStream(),true);
				BufferedReader br=new BufferedReader(new InputStreamReader(s.getInputStream()));
				pw.println("Enter your email-id:");
				id=br.readLine();
				if(registerId(id,this))
				{
					pw.println("Hi"+id+",you are successfully logged in.");
	}
				else
				{
					pw.println("OOPs!Your id seems to be duplicate.Closing your connection..");
					s.close();
					return;
				}
				while(true)
				{
					System.out.println("Menu\n1)Send Mail\n2)Inbox\n3)Logout");
					int opt=Integer.parseInt(br.readLine());
					switch(opt)
					{

						case 1	:	System.out.println("Enter Reciver Address : ");
								String to=br.readLine();
								System.out.println("Enter Message : ");
								String body=br.readLine();
								sendMessage(id,to,body);
								pw.println("Mail sent to"+to);
								break;

						case 2	:	ArrayList<message>al=getMessages(id);
								if(al==null)
								{
									pw.println(0);
									break;
								}
								for(int i=0;i<al.size();i++)
								{
									message m=al.get(i);
									pw.println("From."+m.from);

									pw.println("Message."+m.message);
								}
								break;
						case 3	:	pw.println("You are successfully logged out ..");
								logout(id);
								s.close();
								break;
						default	:	break;
					}
				}
			} catch(Exception e){}
		}
	}
}