JDK Tutorials - Herong's Tutorial Examples - v6.32, by Herong Yang
DatagraClient.java - A Datagram Client Application
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) HerongYang.com. All Rights Reserved. */ 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 sent 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:
herong> java DatagramClient.java 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.
Table of Contents
Date, Time and Calendar Classes
Date and Time Object and String Conversion
Number Object and Numeric String Conversion
Locales, Localization Methods and Resource Bundles
Calling and Importing Classes Defined in Unnamed Packages
HashSet, Vector, HashMap and Collection Classes
Character Set Encoding Classes and Methods
Encoding Conversion Programs for Encoded Text Files
►Datagram Network Communication
Establishing a Datagram Communication Link
DatagramServer.java - A Datagram Server Application
►DatagraClient.java - A Datagram Client Application
DOM (Document Object Model) - API for XML Files
DTD (Document Type Definition) - XML Validation
XSD (XML Schema Definition) - XML Validation
XSL (Extensible Stylesheet Language)
Message Digest Algorithm Implementations in JDK
Private key and Public Key Pair Generation
PKCS#8/X.509 Private/Public Encoding Standards
Digital Signature Algorithm and Sample Program
"keytool" Commands and "keystore" Files
KeyStore and Certificate Classes
Secret Key Generation and Management
Cipher - Encryption and Decryption
The SSL (Secure Socket Layer) Protocol
SSL Socket Communication Testing Programs