Client / Server Programming
in Java
Client / Server in Java
• Primary communications is through sockets.
– (Web type access also available through URL class)
• Browser security limits the access that a program
can have when run as an applet. (Typically
limited to opening a socket back on its host
machine). So.. applets are typically clients.
• “Default” socket is stream (TCP).
• Socket classes implemented in java.net package
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Basic Sockets Classes
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Socket
ServerSocket
SocketAddress
InetAddress
Datagram Socket
Datagram Packet
Multicast Socket
URL
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Socket Client/Server in Java
• Typically client is applet, but can be command
line or graphical application
• Server is written as java application or even in
some other language (c, c++, etc.).
• Where client access is through the Web , the
server must be running on the web server
machine.
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TCPecho / TCPechos
C:\data\cs423_sp12\java\TCPechos\dist>java -jar TCPechos.jar 3456
Serv: Initializing to port 3456
Serv: Waiting for a connection...
Serv: Receved a connection
*---------------*
Srx: Connected to: /127.0.0.1:12405
We just received: (14) This is a test
We just received: (20) This is another test
Srvx disconnected from /127.0.0.1
*---------------------*
Serv: Waiting for a connection...
C:\data\cs423_sp12\java\TCPechos\dist>
C:\data\cs423_sp12\java\basicTCPecho\dist>java -jar basicTCPecho.jar localhost 3456
Enter text to read: This is a test
Client: Rcvd from server: This is a test (14 bytes)
Enter text to read: This is another test
Client: Rcvd from server: This is another test (20 bytes)
Enter text to read: bye
C:\data\cs423_sp12\java\basicTCPecho\dist>
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Iterative TCP echo Server
package tcpechos;
import java.net.*;
import java.io.*;
public class TCPechos {
public static void main(String[] args)
{
Socket sock;
ServerSocket ssock;
InputStream isIn;
PrintStream psOut;
int iNumRead, numPort;
String sendMsg, port = "5678";
byte abIn[] = new byte[1024];
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Iterative TCP echo Server
// Handle command line arguments
switch (args.length)
{
case 1:
port = args[0];
break;
case 0:
break;
default:
System.out.println("Illegal number of arguments.");
System.exit(1);
}
numPort = Integer.parseInt(port); //port number must be an int for Socket
System.out.println ("Serv: Initializing to port " + numPort);
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Iterative TCP echo Server
try
{
// Create the server socket and bind it to our port
ssock = new ServerSocket (numPort);
while (true)
{
// Wait for a client request
System.out.println ("Serv: Waiting for a connection...");
sock = ssock.accept();
// We got a connection request! Print out info and start talking
System.out.println ("Serv: Receved a connection");
System.out.println ("*---------------*");
System.out.println ("Srx: Connected to: " +sock.getInetAddress()
+ ":" +sock.getPort());
psOut = new PrintStream (sock.getOutputStream());
isIn = sock.getInputStream();
iNumRead = 0;
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Iterative TCP echo Server
while (iNumRead >= 0)
{ //Keep reading as long as we get data
iNumRead = isIn.read(abIn, 0, 1024);
if (iNumRead < 0)
break;
sendMsg = new String(abIn,0,iNumRead);
System.out.println("We just received: (" +iNumRead + ") " + sendMsg);
//Note that the received message includes '\n' and
//we add one of our own with println
psOut.print(sendMsg);
iNumRead = 0;
}
sock.close();
System.out.println ("Srvx disconnected from " + sock.getInetAddress());
System.out.println ("*---------------------*");
} //end of while
} //end of try
catch (Exception e)
{ System.err.println (":Serv: Exception in main: " + e); }
} //end of main()
} //end of TCPechos
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Basic TCP echo Client
import java.io.*;
import java.util.*;
public class BasicTCPecho
{
public static void main(String[] args) {
// TODO code application logic here
Socket sock;
String sIn, host = "localhost", port = "5678"; //default host and port
InputStream isIn;
PrintStream psOut;
byte abIn[] = new byte[1024];
int iNumRead, numPort;
Scanner input;
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Basic TCP echo Client
// Deal with any command line arguments
switch (args.length)
{
case 2:
port = args[1];
case 1:
host = args[0];
break;
case 0:
break;
default:
System.out.println("Illegal number of arguments.");
System.exit(1);
}
numPort = Integer.parseInt(port); //port number must be an int for Socket
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Basic TCP echo Client
try
{
sock = new Socket(host, numPort);
isIn = sock.getInputStream();
psOut = new PrintStream(sock.getOutputStream());
input = new Scanner (System.in);
while (true) {
//First we get some text from the user.
System.out.print("Enter text to read: ");
sIn = input.nextLine();
//If we typed “bye”, then exit client
if (sIn.equals("bye")) {
sock.close();
break;
}
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Basic TCP echo Client
//next we send that to the server
psOut.print(sIn);
//Now, wait for something to come back...
iNumRead = isIn.read(abIn,0,1024);
if (iNumRead < 0)
{
break; //connection has been closed
}
String str = new String(abIn,0,iNumRead);
System.out.println("Client: Rcvd from server: " + str +
" (" + iNumRead + " bytes)");
}
sock.close();
}
catch (Exception e)
{ System.out.println("Client: exception " + e); }
}//end of main
}//end of class
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Threads in Java
• Multithreading built into Java language
• Thread (String threadName)
• Thread ( ) (named “Thread- + number”))
• Thread States
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born
ready
running
waiting
sleeping
dead
blocked
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Thread State Diagram
born
ready
running
waiting
sleeping
dead
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Thread Priorities
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Priority range 1 to 10
Thread.MIN_PRIORITY = 1;
Thread.MAX_PRIORITY = 10;
Thread.NORM_PRIORITY = 5;
Thread.setPriority (int);
Thread.getPriority( );
Threads processed in priority order, with roundrobin processing within a priority
• Starvation possible
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Thread class
public class Thread extends Object implements Runnable
{
Thread ( );
Thread (Runnable object);
run ( );
start ( );
getPriority ( );
sleep ( );
wait ( );
notify ( );
....
;
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Implementing Threads (1)
Subclassing the Thread class
class MyNuThread extends Thread {
private data ....;
public MyNuThread ( ) {
do constructor stuff here;
}
public void run( )
{
here’s where work is done
}
}
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Using Threads (1)
MyNuThread thread1 = new MyNuThread ( );
thread1.start( );
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Implementing Threads (2)
Make an existing class runnable
class ServerExtension implements Runnable {
private data....;
public ServerExtension( ) {
do constructor stuff here;
}
public void run( ) {
do work stuff here
}
}
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Using extended classes
ServerExtension servx = new ServerExtension( );
Thread thServx = new Thread (servx);
thServx.start();
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Multi-threaded server Output
C:\data\cs423_sp12\java>java -jar TCPechod.jar
Serv: Initializing to port 3456
Serv: Waiting for a connection...
Serv: Received connection 1
Serv: Waiting for a connection...
*---------------*
Srx: Connected to: /127.0.0.1:47871
We just received: (21) This is from client 1
Serv: Received connection 2
Serv: Waiting for a connection...
*---------------*
Srx: Connected to: /127.0.0.1:47872
We just received: (21) This is from client 2
We just received: (29) This is another from client 1
We just received: (22) We're back to client 2
Srvx disconnected from /127.0.0.1
*---------------------*
Srvx disconnected from /127.0.0.1
*---------------------*
Srvx disconnected from /127.0.0.1
*---------------------*
Srvx disconnected from /127.0.0.1
*---------------------*
C:\data\cs423_sp12\java\basicTCPecho\dist>java -jar
basicTCPecho.jar localhost 3456
Enter text to read: This is from client 1
Client: Rcvd from server: This is from client 1 (21 bytes)
Enter text to read: This is another from client 1
Client: Rcvd from server: This is another from client 1 (29 bytes)
Enter text to read: bye
C:\data\cs423_sp12\java\basicTCPecho\dist>java -jar
basicTCPecho.jar localhost 3456
Enter text to read: This is from client 2
Client: Rcvd from server: This is from client 2 (21 bytes)
Enter text to read: We're back to client 2
Client: Rcvd from server: We're back to client 2 (22 bytes)
Enter text to read: bye
C:\data\cs423_sp12\java\basicTCPecho\dist
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Multi-threaded TCPecho Server
package tcpechod;
import java.net.*;
import java.io.*;
public class TCPechod {
public static int counter = 0;
public static void main(String[] args) {
Socket sock;
ServerSocket ssock;
Thread thServx;
ServerExtension servx;
System.out.println ("Serv: Initializing to port 3456");
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Multi-threaded TCPecho Server
try
{
ssock = new ServerSocket (3456);
while (true) {
System.out.println ("Serv: Waiting for a connection...");
sock = ssock.accept();
counter++;
System.out.println ("Serv: Received connection " + counter);
servx = new ServerExtension(sock);
String name = Integer.toString(counter);
thServx = new Thread (servx, name);
thServx.start();
}
}
catch (Exception e)
{ System.err.println (":Serv: lException in main: " + e); }
}
}
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Multi-threaded TCPecho Server
class ServerExtension implements Runnable {
private Socket sock;
private InputStream isIn;
private PrintStream psOut;
private String count;
public ServerExtension (Socket s) {
sock = s;
count = Integer.toString(TCPechod.counter);
}
public void run () {
int iNumRead;
String sendMsg;
byte abIn[] = new byte[1024];
System.out.println ("*---------------*");
System.out.println("Srx: Connected to: " + sock.getInetAddress() + ":“
+sock.getPort());
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Multi-threaded TCPecho Server
try
{
psOut = new PrintStream (sock.getOutputStream());
isIn = sock.getInputStream();
iNumRead = 0;
while (iNumRead >= 0)
{
iNumRead = isIn.read(abIn, 0, 1024);
if (iNumRead < 0)
break;
sendMsg = new String(abIn,0,iNumRead);
System.out.println("We just received: (" +iNumRead + ") " + sendMsg);
//Note that the received message includes '\n' and
//we add one of our own with println
psOut.print(sendMsg);
iNumRead = 0;
} // end of while
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Multi-threaded TCPecho Server
sock.close();
System.out.println ("Srvx disconnected from " + sock.getInetAddress());
System.out.println ("*---------------------*");
}//end of try
catch (Exception e)
{
System.err.println (":Serv: Exception in main: " + e);
}
System.out.println ("Srvx disconnected from " + sock.getInetAddress());
System.out.println ("*---------------------*");
}
}
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NetBeans Graphical Client
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NetBeans Project
• TCPecho
– build
– dist
• TCPecho.jar
– nbproject
– src
• META-INF
• tcpecho
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–
–
resources
TCPechoAboutBox.form
TCPechoAboutBox.java
TCPechoApp.java
TCPechoView.form
TCPechoView.java
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NetBeans Project Structure
• TCPechoApp.java
– Basic application shell.
– Application class with main() method
– startup() method creates and shows TCPechoView
• TCPechoView.java
– In NetBeans 7.0, GUI built drag-and-drop. Code generated
from objects created.
– Actions added to buttons by identifying ActionPerformed
methods and then adding in actions to that method.
• TCPechoAboutBox.java
– Automatically constructed dialog box.
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NetBeans Project Layout
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UDP Temperature Server
import java.net.*;
import java.io.*;
class TempServer
{
public static void main (String argv[])
{
DatagramSocket sock;
DatagramPacket sendPacket, recvPacket;
int tempF;
int tempC;
try
{
sock = new DatagramSocket (5678);
System.out.println ("Serv: Bound to port 5678");
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UDP Temperature Server
while (true)
{
System.out.println ("Serv: Waiting for a request...");
byte data[] = new byte[25];
recvPacket = new DatagramPacket (data, data.length);
sock.receive(recvPacket);
System.out.println ("Serv: Received a packet...");
String tempFs = new String(recvPacket.getData(),0,recvPacket.getLength());
tempF = Integer.parseInt(tempFs);
tempC = (int)(5*(tempF -32)/9);
String tempCs = Integer.toString(tempC);
data = tempCs.getBytes();
sendPacket = new DatagramPacket (data, data.length, recvPacket.getAddress(),
recvPacket.getPort());
sock.send(sendPacket);
System.out.println("We got a temp of " + tempFs + " and returned " + tempCs);
}
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UDP Temperature Server
}
catch (Exception e)
{
System.err.println (":Serv: lException in main: " + e);
}
}//end of main
}//end of class
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Graphical UDP Temperature Client
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Graphical UDP Temperature Client
import java.awt.*, javax.swing.* java.awt.event.* java.net.* java.io.*;
public class udpTemp extends JFrame implements WindowListener,
ActionListener{
udpTemp() //Build graphical layout
public void actionPerformed(ActionEvent evt) // handle events
public static void main (String[] args)
// start the program
public void windowClosing(WindowEvent e) //Handle Window events
private TextField portField;
:
private DatagramSocket sock;
}//end of class
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UDP Temp Client - constructor
udpTemp() {
setTitle("UDP Temp Demo");
setSize(400,300);
addWindowListener (this);
//setBackground(Color.blue);
bgColor = new Color(16, 134, 197);
setLayout(new BorderLayout());
Panel p = new Panel();
p.setBackground(bgColor);
p.setLayout(new FlowLayout());
Button convertButton = new Button("Convert");
convertButton.addActionListener(this);
p.add(convertButton);
hostField = new TextField("localhost", 25);
p.add(hostField);
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UDP Temp Client - constructor
portField = new TextField("5678", 6);
p.add(portField);
add("North",p);
Panel p2 = new Panel();
p2.setLayout(new FlowLayout());
p2.setBackground(bgColor);
tempFField = new TextField("75", 4);
p2.add(tempFField);
tempCField = new TextField("", 4);
p2.add(tempCField);
add("Center",p2);
Panel p3 = new Panel();
p3.setBackground(bgColor);
resultField = new TextArea("results...",8,40);
p3.add(resultField);
add("South",p3);
}//end of constructor.
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UDP Temp Client - actionPerformed
public void actionPerformed(ActionEvent evt)
{
InetAddress ia = null;
InputStream isIn;
PrintStream psOut;
byte abIn[] = new byte[1024];
byte abOut[] = new byte[1024];
int iNumRead, iNumSent;
if (evt.getActionCommand().equals("Convert"))
{
int portNumber = (new Integer(portField.getText())).intValue();
String s1 = "The port number is " + portNumber + "\n";
resultField.setText(s1);
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UDP Temp Client - actionPerformed
try
{
String hostName = hostField.getText();
s1 = "The host is " + hostName + "\n";
resultField.append(s1);
ia = InetAddress.getByName(hostName);
sock = new DatagramSocket ();
String tempF = tempFField.getText();
s1 = "The temperature is " + tempF + "\n";
resultField.append(s1);
abOut = tempF.getBytes();
sendPacket = new DatagramPacket (abOut, abOut.length, ia, portNumber);
sock.send (sendPacket);
s1 = "We just sent a packet\n";
resultField.append(s1);
recvPacket = new DatagramPacket (abIn, abIn.length);
sock.receive(recvPacket);
String str = new String (recvPacket.getData(), 0, recvPacket.getLength());
tempCField.setText(str);
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UDP Temp Client - actionPerformed
}
catch (Exception exc) {
System.out.println ("Clnt: Exception reading server data: " + exc);
}
}//end of if Convert...
}//end fo ActionPerformed
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UDP Temp Client – window
methods
public void windowClosing(WindowEvent e) {
try {
String s1 = "Goodbye ...";
resultField.setText(s1);
Thread.sleep(750);
}
catch (Exception exc) { System.out.println("Exception" + exc); }
System.exit(0);
}
public void windowOpened(WindowEvent e) {
System.out.println ("Opening Window"); }
public void windowClosed(WindowEvent e) {}
public void windowIconified(WindowEvent e) {}
public void windowDeiconified(WindowEvent e) {}
public void windowActivated(WindowEvent e) {}
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UDP Temp Client – private data
private Color bgColor;
private TextField portField;
private TextField hostField;
private TextField tempFField;
private TextField tempCField;
private TextArea resultField;
private DatagramPacket sendPacket, recvPacket;
private DatagramSocket sock;
}//end of class
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Summary
• Java Client / Server Introduction
– Basic processes / classes
•
•
•
•
Basic TCPecho Client / Server
Threads in Java
Multi-threaded TCPecho Server
Graphical TCPecho Client
– NetBeans Project
• UDP Temperature Server
• Graphical UDP Temperature Client
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