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port number

Sanjul Jain

Joined: Oct 21, 2004
Posts: 14

Instead of giving default value of port number 7777, I want to

let user specify the value of port number.

Can you please help me out.


Here is my code:

//server code:
import java.io.*;
import java.net.*;
import java.lang.*;
import java.util.*;

class TCPAdditionServer1{
public static void main(String[] argv)throws Exception{
String clientSentence,capitalizedSentence;
int sum=0;
String sumString = "";
InetAddress serverAddress;

int listen_port = 7777;
//int listen_port = Socket.getLocalPort();

//ServerSocket welcomeSocket=new ServerSocket(7777);
ServerSocket welcomeSocket=new


//ServerSocket welcomeSocket=new


//int cpn = welcomeSocket.getLocalPort();
// System.out.println(" get local port: " + cpn);

//int cpn1 = welcomeSocket.getPort();
//System.out.println(" get remote port: " + cpn1);

// welcomeSocket(cpn);


Socket connectionSocket = null;

try {
} catch (IOException e) {
System.out.println("Accept failed:");

BufferedReader inFromClient=new BufferedReader(new


DataOutputStream outToClient=new


StringTokenizer st= new

while(st.hasMoreTokens()) {
sum += Integer.parseInt(st.nextToken());

int clientPortNumber =

System.out.println("Waiting for connections on

port " + clientPortNumber + " ... ");

System.out.println("Received connection from "

+ connectionSocket.getRemoteSocketAddress());

sumString = Integer.toString(sum);
clientSentence = " ";
capitalizedSentence = clientSentence + sumString +




//client code
import java.io.*;
import java.net.*;
import java.net.InetAddress;

class TCPAdditionClient1{
public static void main(String[] argv)throws Exception{
String sentence,sentc,portNumberString;
int portNumber= 7777;
String modifiedSentence;
InetAddress clientAddress;
BufferedReader inFromUser1=new BufferedReader(new

BufferedReader inFromUser2=new BufferedReader(new

BufferedReader inFromUser3=new BufferedReader(new

InputStreamReader(System.in)); //portNumberString


System.out.println("Enter port number (Press Enter for

default value(7777)): ");
portNumberString = inFromUser3.readLine();

int portNumberInteger =


portNumber = portNumberString.length() == 0 ? 7777 :


//System.out.println("port number:" + portNumber);


System.out.println("Enter hostname or IP of server:

(Press Enter for default value(localhost)): ");
sentc = inFromUser1.readLine();

String hostName = sentc.length() == 0 ? "localhost" :

Socket clientSocket=new Socket(hostName,portNumber);

SocketAddress sa =


if (clientSocket.isConnected()== true);
System.out.println("Connecting to server " + "'" + sa

+ "'" + "..." + " Connected.");

DataOutputStream outToServer=new

BufferedReader inFromServer=new BufferedReader(new


System.out.println("Enter a string of integers

seperated by non-numeric characters:");
sentence = inFromUser2.readLine();

System.out.println("From Server----->The Sum



} catch(UnknownHostException e) {
System.err.println(" Don't know about host: ");
} catch(IOException e) {
System.err.println(" Couldn't get I/O for the



Stefan Wagner
Ranch Hand

Joined: Jun 02, 2003
Posts: 1923

When posting code, please use the code-tags.

You may edit your post, and insert them later, if you forgot them - i.e.: now.

To the content of your question:
Normally, a service is running on a server, allowing multiple clients to connect to it.
The port is a kind of adress, where the service is reachable.

The server is started (months) before the client requests it.

How can the client inform the server, that it likes to access the service on port xy?
And why?

Do you want to start a server for every client?
When the first client begs to use Port 7778, and the second client likes to have it waiting on 7776?

What if the client is asking for a port already in use - i.e.: port 80, 21, 7 or some other well known port?

You may start a server on port 7777, to wait for the information of client where to listen, and start a new Thread, listening on that port.
But you only moved the fixed port to another level.

Think about the port-number like your telephone-number.
People who want to call you need to know your number, and cannot specify the number, under which they want to reach you.
You could give them a primary-request number, where they may call you, and tell you 'I want to reach you under 666-44-345', and you could then call your telephone-company, and ask them, to get a second telephone number '666-44-345', and if it is possible - the number isn't in use right now, wait on the call on your second phone.
But why?

Additional hints:
You needn't import java.lang.*;

And if you open a stream for reading (from System.in or whereether), you don't need a new Streamobject for every readLine()-call.
Generate one object, and read from that:

[ October 24, 2004: Message edited by: Stefan Wagner ]

I agree. Here's the link: http://aspose.com/file-tools
subject: port number
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