prevent multiple instances of same server

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Java

import java.io.*;
import java.net.*;
class EchoServer 
{
    public static void main(String args[]) throws Exception
    {
        String clientstr;
	String fwdstr;
	ServerSocket ssock = new ServerSocket(5678);
		
	while(true) 
	{
	    Socket conn = ssock.accept();
			
	    BufferedReader inFromClient =new BufferedReader(new InputStreamReader(conn.getInputStream()));
	    DataOutputStream outToClient =new DataOutputStream(conn.getOutputStream());
			
            clientstr = inFromClient.readLine();
	    System.out.println("Input from the Client: "+clientstr);
	    fwdstr = clientstr+ '\n';
	    outToClient.writeBytes(fwdstr);
	}
    }
}

this is an echo server..i would like to know how could i make sure that multiple instances of this server is not running elsewhere??? please help..