This section provides a tutorial example on how to write a network application, DatagraClient.java, that creates a client socket, sends datagram packet to a datagram server.
The following program, called DatagraClient, acts as a client program to
DatagramServer. It repeatedly sends a datagram packet to DatagramServer,
and waits a return datagram packet:
/**
* DatagramClient.java
* Copyright (c) 2002 by Dr. Herong Yang
*/
import java.io.*;
import java.net.*;
public class DatagramClient {
public static void main(String[] args) {
BufferedReader in = new BufferedReader(new InputStreamReader(
System.in));
PrintStream out = System.out;
byte[] buf = new byte[1024];
try {
DatagramPacket dp = new DatagramPacket(buf, buf.length);
dp.setAddress(InetAddress.getByName("localhost"));
dp.setPort(7777);
// binding to the default address and any free port
DatagramSocket ds = new DatagramSocket();
printDatagramSocketInfo(ds);
String m = null;
while (true) {
// sending the text line from console to the remote system
m = in.readLine();
byte[] b = m.getBytes();
dp.setData(b);
dp.setLength(b.length);
ds.send(dp);
// sending the text line from the remote system to console
dp.setData(buf);
ds.receive(dp);
m = new String(buf, 0, dp.getLength());
out.println(m);
if (m.equals(".")) break;
}
} catch (IOException e) {
System.err.println(e.toString());
}
}
private static void printDatagramSocketInfo(DatagramSocket s) {
System.out.println("Datagram Socket Info:");
if (s.isConnected()) {
System.out.println(" Connected to a remote system.");
System.out.println(" Remote address = "
+s.getInetAddress().toString());
System.out.println(" Remote port = "
+s.getPort());
} else {
System.out.println(" Not connected to a remote system.");
}
System.out.println(" Local socket address = "
+s.getLocalSocketAddress().toString());
System.out.println(" Local address = "
+s.getLocalAddress().toString());
System.out.println(" Local port = "
+s.getLocalPort());
}
}
One DatagramPacket object is used for both sending data and receiving data.
Two byte arrays are used in the program, "buf" contains the data received,
"b" contains the data to be send out.
With DatagramServer running in a command window, run DatagramClient in
another command window, and type in
Fish, I love you and respect you very much.
But I will kill you dead before this day ends.
.
You will see:
Datagram Socket Info:
Not connected to a remote system.
Local socket address = 0.0.0.0/0.0.0.0:1035
Local address = 0.0.0.0/0.0.0.0
Local port = 1035
Fish, I love you and respect you very much.
.hcum yrev uoy tcepser dna uoy evol I ,hsiF
But I will kill you dead before this day ends.
.sdne yad siht erofeb daed uoy llik lliw I tuB
.
Note that the datagram socket constructor automatically picked up
a free local port, 1035.
In the DatagramServer window, you will see the following output:
Datagram Socket Info:
Not connected to a remote system.
Local socket address = 0.0.0.0/0.0.0.0:7777
Local address = 0.0.0.0/0.0.0.0
Local port = 7777
Datagram Packet Info:
Remote socket address = /127.0.0.1:1035
Remote address = /127.0.0.1
Remote port = 1035
Data length = 43
Datagram Socket Info:
Not connected to a remote system.
Local socket address = 0.0.0.0/0.0.0.0:7777
Local address = 0.0.0.0/0.0.0.0
Local port = 7777
Datagram Packet Info:
Remote socket address = /127.0.0.1:1035
Remote address = /127.0.0.1
Remote port = 1035
Data length = 46
Datagram Socket Info:
Not connected to a remote system.
Local socket address = 0.0.0.0/0.0.0.0:7777
Local address = 0.0.0.0/0.0.0.0
Local port = 7777
Datagram Packet Info:
Remote socket address = /127.0.0.1:1035
Remote address = /127.0.0.1
Remote port = 1035
Data length = 1
As you can see, DatagramServer and DatagramClient worked perfectly. You
can even run multiple instances of DatagramClient, and DatagramServer will
handle them correctly.
