Jan. 2004 1

Java Networking TCP

Yangjun Chen

Dept. Business ComputingUniversity of Winnipeg

Jan. 2004 2

PortsPorts

• In general, computers only have one Internet address, but computers usually need to communicate with more than one host at a time.

• Ports map incoming data to a particular• process or application running on a computer,• With every socket, there needs to be an associated port number• Example - regular post. The IP address is like the street

address while the port number would represent the house number.

Jan. 2004 3

Sever - client communicationSever - client communication

• A socket can be considered as a connection point.

IP addressIP address

port1port1 portportNN

IPIPss

… … ......

IPIPcc

… … ... ...

Port’1Port’1 Port’Port’MM

IP addressIP address

SEVER:SEVER:

CLIENT:CLIENT:

SocketSocketss(Ip(Ipcc, Port’s, Port’sMM, port1), port1)

SocketSocketcc(Ip(Ipss, Port1, port’, Port1, port’MM))

Jan. 2004 4

PortsPorts

• Ports can range in value from 1 to 65535, with ports 1 to 1023 being reserved for root access in Unix.

• On Windows NT, 95 and Macs, any user can listen on any port.

• Only one program can listen on a given TCP port at the same time.

• However, many remote hosts can connect to the same remote port.

Jan. 2004 5

Internet Addresses

• Every computer on the net has an associated four-byte IP address that is unique. Usually represented in dotted quad format like 148.131.31.1. where each byte is an unsigned value in the range of 0 to 255.

• Since numbers are hard to remember, these numbers are mapped into names like www.uwinnipeg.ca or www.umanitoba.ca.

• It's the numerical address that is fundamental, not the name. You can have multiple names that represent the same IP address.

Jan. 2004 6

Internet Addresses

• java. net. InetAddress class are used to manage such addresses.• Some are shown here: -

- InetAddress getByName(String host)- InetAddress[] getAllByName(String host)- InetAddress getLocalHost() - String getHostName()- byte[] getHostAddress() - boolean isMulticastAddress()

Jan. 2004 7

Creating InetAddress Objects

• The InetAddress class is unusual in that it doesn't have a public constructor, so to create an object you would pass in the hostname or string format of the dotted quad address into the staticmethod:

InetAddress.getByName( )

Jan. 2004 8

Creating InetAddress Objects

import java.net.*;class ibm{

public static void min (String args[]) { try (

InetAddress[] addresses = InetAddress.getAllEyName(" www.ibm.com");for (int i = 0; i<addresses.length;i++)

System.out.println(addresses[i]);}//trycatch (UnknownHostException e) {}

}//main }//class

Jan. 2004 9

Creating InetAddress Objects

• To create an InetAddress that refers to your own machine use the static getLocalHost() method.

try {InetAddress me = InetAddress.getLocalHost( );

}//trycatch (UnknownHostException e) {

System.err.println( );}//catch

Jan. 2004 10

Parsing InetAddress

• Given an InetAddress, we might want to know the host name or it's IP address as a string or byte array.

ImporL java.net.*;public class address{

public static void main(String args[]) {try {

InetAddress me = new netAddress.getLocalHost(); System.out.println(me.getHostName()); System.out.println(me.getHostAddress());

Jan. 2004 11

Parsing InetAddress

byte[] quad = me.getAddress();for(int i = 0; i < quad.length; i++)

System.out.print(quad[i] + ”.”);System.out.println();

}//trycatch (UnknownHostException e) {

( System.err.println(e);}//catch

}//main }//class

Jan. 2004 12

TCP

• TCP (Transmission Control Protocol) - a connection-based protocol that provides a reliable flow of data

between two computers.- It allows retransmission of lost data.- It provides multiple paths through different routers in case one goes

down.- Bytes are delivered in the order they are sent.

• Applications using TCP to communicate- HTTP, FTP, Telnet, etc.

Jan. 2004 13

TCP

• Java networking classes use TCP

• java.net package provides the functionality for networking

- java.net

. URL()

. URLConnection()

. Socket()

. SocketServer()

Jan. 2004 14

Sockets

• Host's native networking s/w handles the splitting of data into packets on the transmitting side of a connection, and the reassembly of packets on the receiving side.

• Java programmers are presented with a higher level abstraction called a socket.

Jan. 2004 15

Sockets

• A socket represents a reliable connection for data transmission between two hosts.

• Four fundamental operations- 1. Connect to a remote machine- 2. Send data- 3. Receive data- 4. Close the connection

Jan. 2004 16

Establishing a Connection

• Accomplished through the class constructors:

- java.net.Socket(). client side implementation

- java.net.ServerSocket(). server side implementation

• Each socket is associated with exactly one host.

• To connect to a different host, a new socket object must be created.

Jan. 2004 17

Sending/Receiving Data

• Sending and Receiving data is accomplished with input and output streams.

- public InputStream getInputStream()

- public OutputStream getOutputStream()

- both of these classes throw an IOException

Jan. 2004 18

Closing a Connection

• There's a method to close a socket.- public synchronized void close()- this method throws an IOException as well.

• For a well behaved program, we need to close the I/O streams as well.

• Close any streams connected to a socket before closing the socket.- OutStream.close()- InStream.close()- Socket.close()

Jan. 2004 19

Example: EchoTest(l)

import java.io.*; import java.net.*,

public class EchoTest {public static void main(String[] args) {

String host="truffle";Socket eSocket = null;DataoutputStream os = null;DataInputstream is = null;DataInputStream stdIn = new DataInpuuStream(System.in);

Jan. 2004 20

Example: EchoTest(2)

try {eSocket = new Socket(host,7);os = new DataOutputStream(eSocket.getOutputStream());is = new

DataTnputStream(eSocket.getInputStream()); }//trycatch (UnknownHostException e) {

System.err.println(“Unknown host: "+host); }//catchcatch (IOException e) {

System.err.println("No I/O connection to: “ + host);}///catch

Jan. 2004 21

Example: EchoTest(3)

if (eSocket !=null && os!=null && is!=null) {try {

String uTnput;while ((uInput=stdIn.readLine()) != null) {

os.writeBytes(userlnput);os.writeByte('\n');System.out.println("echo:

+is.readLineo);if (userInput.equals("quit”))

break; }//whileos.close();is.close();

Jan. 2004 22

Example: EchoTest(4)

eSocket.close(); }//try catch (IOException e)System.err.println("I/O failed on the connection to: “ + host); }//catch

}//if }//try

}//class

Jan. 2004 23

Example: Chat Client(l)

import java.io.*;import java.net.*;import RcveData;import SendData;

public class chat_client extends Thread {

public static void main(String a[]) throws IOException {Socket sock = null;String host = “localhost";int port 9100;

Declaring a Declaring a Socket objectSocket object

Jan. 2004 24

Example: Chat Client(2)

if (a.length > 1) {port = Integer.parseInt(a[i]);

} //ifif (a.length > 0) {

host = a[0];}//ifSystem.out.println("using port “+ port + “connecting to “ + host);try {

sock = new Socket(host,port);}//try

Establish a connectionto the specified bost and port

Jan. 2004 25

Example: Chat Client(3)

catch (java.net.ConnectException e){ System.out.println(e);System.exit(0);

}//catchSendData sd = new SendData(sock);RcveData rd = new RcveData(sock);

sd.start();rd.start();}//main

}//chat_client

Instantiate thesupporting classes

Jan. 2004 26

Server Sockets

• A host that responds to a connection.

• Instead of connecting to a remote host, a server program will wait for others to connect to it.

Jan. 2004 27

Accepting Connections

• 1) A server socket binds to a particular port.• 2) It then listens for connection attempts.• 3) When it detects an attempt, it will accept the connection.

- public Socket accept() Throws IOException• The accept () method blocks until a connection is detected.• It returns a java. net. Socket Object that is used to perform the

communication.

Jan. 2004 28

Server Sockets

• Multiple clients can connect to the same port on a server at any time.

• The data are distinguished by the port numbers and the client addresses.

• However, no more than one socket can listen to a particular port at a time.

• This is why servers tend to be heavily multithreaded.• Generally, the server socket listening to the port will accept

connections and then pass the actual processing to other threads.

Jan. 2004 29

Server Sockets:Queue

• Incoming connections are stored in a FIFO queue until the server can accept them.

• If the queue is full, then connection attempts will be refused until space opens up.

• The default queue length for most systems is between 5 and 50.

Jan. 2004 30

Server Sockets:Queue

• The length of the queue can be adjusted by passing in the size of the queue in the “backlog" parameter.

- public ServerSocket(int port,int backlog)

• Each system has a maximum queue length, so any values for the queue length longer than the maximum will be set to the maximum.

Jan. 2004 31

Example: Chat Server(l)

//This is a simple chat server written in Java

import java.io.*;*import java.net.*;import RcveData;import SendData;

public class chat_server extends Thread {

Jan. 2004 32

Example: Chat Server(2)

public static void main(String a[]) {int blog = 600;int port = 9100;Socket sock = null;

if (a.length > 0) { port = Integer.parseInt(a[0]);

}//if ServerSocket servsock - null;

Jan. 2004 33

Example: Chat Server(3)

System.out.println("using port “ + port); try {

servsock = new Serversocket(port,blog);}// trycatch (java.io.IOException e) {

System.out.println(e);System.exit(0);

}//catchtry {

sock = servsock.accept();} //try

Jan. 2004 34

Example: Chat Server(4)

catch (java.io.IOException e) {System.out.println(e);System.exit(0); )

}//catch

SendData Sd = new SendData(sock);RcveData rd = new RcveData(sock);

sd.start();rd.start();

}//main}//class

Jan. 2004 35

Example: Send Data(1)

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

public class SendData extends Thread {Socket sock;public SendData(Socket sock) {

this.sock = sock;}//SendData constructor

public void run() {String line;

Jan. 2004 36

Example: Send Data(2)

try {outputStreamWriter outw = new

outputStreamwriter(sock.getOutputStream());BufferedWriter sockout=new BufferedWriter(outw);TnputStreamReader inr = new InputStreamReader(System.in);BufferedReader in = new BufferedReader(inr);while ((line = in.readLine()) != null) {

sockout.write(line+"\n");

Jan. 2004 37

Example: Send Data(3)

sockout.flush(); yield();

}//while}//trycatch (java.io.IOException e) {System.out.println(e);System.exit(0);

}//catch}//run

}//SendData

Jan. 2004 38

Example: Receive Data(1)

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

public class RcveData extends Thread {Socket sock;

public RcveData(Socket sock) {this.sock = sock;

}

public void run() {String line;

Jan. 2004 39

Example: Receive Data(2)

try {InputStreamReader inr = new

InputStreamReader(sock.getInputStream());BufferedReader in = new BufferedReader(inr);

while (line = in.readLine( )) != null) {

System.out.print(“Receiving: ”);System.out.println(line);yield();

}//while}//try

Jan. 2004 40

Example: Receive Data(3)

catch (java.io.IOException e) {system.out.println(e); System.exit(0);

}//catch}//run

}//RcveData