JDK Tutorials - Herong's Tutorial Examples - v6.32, by Herong Yang
DatagramServer.java - A Datagram Server Application
This section provides a tutorial example on how to write a network application, DatagramServer.java, that creates a datagram server socket and listens for incoming packets.
The following program, called DatagramServer, is a simple datagram socket application, which acts a server listening on given port number for datagram packets to arrive:
/* DatagramServer.java * Copyright (c) HerongYang.com. All Rights Reserved. */ import java.io.*; import java.net.*; public class DatagramServer { public static void main(String[] args) { byte[] buf = new byte[1024]; DatagramPacket dp = new DatagramPacket(buf, buf.length); try { // binding to the default address and port 7777 DatagramSocket ds = new DatagramSocket(7777); printDatagramSocketInfo(ds); while (true) { ds.receive(dp); printDatagramSocketInfo(ds); printDatagramPacketInfo(dp); // no need to call buf = dp.getData(); // reversing the characters, assuming one-type characters int n = dp.getLength(); for (int i=0; i<n/2; i++) { byte t = buf[i]; buf[i] = buf[n-1-i]; buf[n-1-i] = t; } ds.send(dp); } } 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()); } private static void printDatagramPacketInfo(DatagramPacket d) { System.out.println("Datagram Packet Info:"); System.out.println(" Remote socket address = " +d.getSocketAddress().toString()); System.out.println(" Remote address = " +d.getAddress().toString()); System.out.println(" Remote port = " +d.getPort()); System.out.println(" Data length = " +d.getLength()); } }
Whenever DatagramServer receives a datagram packet, it takes the data, reverses the data, and sends the data back to where it comes from.
Run DatagramServer in a command window, you will see the following output:
herong> java DatagramServer.java 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
The server is ready to receive packets at port 7777.
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