echoclient.java

Java网络编程与分布式计算, 主要分析java网络各方面的编程, 提供许多实用安全

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

// Chapter 5, Listing 4
public class EchoClient 
{
	// UDP port to which service is bound
	public static final int SERVICE_PORT = 7;

	// Max size of packet
	public static final int BUFSIZE = 256;

	public static void main(String args[])
	{
		if (args.length != 1)
		{
			System.err.println ("Syntax - java EchoClient hostname");
			return;
		}

		String hostname = args[0];

		// Get an InetAddress for the specified hostname
		InetAddress addr = null;
		try
		{
			// Resolve the hostname to an InetAddr
			addr = InetAddress.getByName(hostname);
		}
		catch (UnknownHostException uhe)
		{
			System.err.println ("Unable to resolve host");
			return;
		}

		try
		{
			// Bind to any free port
			DatagramSocket socket = new DatagramSocket();

			// Set a timeout value of two seconds
			socket.setSoTimeout (2 * 1000);

			for (int i = 1 ; i <= 10; i++)
			{
				// Copy some data to our packet
				String message = "Packet number " + i ;
				char[] cArray = message.toCharArray();					
				byte[] sendbuf = new byte[cArray.length];
				for (int offset = 0; offset < cArray.length ; offset++)
				{
					sendbuf[offset] = (byte) cArray[offset];
				}
	
				// Create a packet to send to the UDP server
				DatagramPacket sendPacket = new DatagramPacket(sendbuf, cArray.length, addr, SERVICE_PORT);

				System.out.println ("Sending packet to " + hostname);

				// Send the packet
				socket.send (sendPacket);

				System.out.print ("Waiting for packet.... ");

				// Create a small packet for receiving UDP packets
				byte[] recbuf = new byte[BUFSIZE];
				DatagramPacket receivePacket = new DatagramPacket(recbuf, BUFSIZE);

				// Declare a timeout flag
				boolean timeout = false;

				// Catch any InterruptedIOException that is thrown
				// while waiting to receive a UDP packet
				try
				{
					socket.receive (receivePacket);
				}
				catch (InterruptedIOException ioe)
				{
					timeout = true;
				}

				if (!timeout)
				{
					System.out.println ("packet received!");
					System.out.println ("Details : " + receivePacket.getAddress() );

					// Obtain a byte input stream to read the UDP packet
					ByteArrayInputStream bin = new ByteArrayInputStream (
					  receivePacket.getData(), 0, receivePacket.getLength() );

					// Connect a reader for easier access
					BufferedReader reader = new BufferedReader ( 
					  new InputStreamReader ( bin ) );

					// Loop indefinitely
					for (;;)
					{
						String line = reader.readLine();
					
						// Check for end of data
						if (line == null)
							break;
						else
							System.out.println (line);
					}				
				}
				else
				{
					System.out.println ("packet lost!");
				}

				// Sleep for a second, to allow user to see packet
				try
				{
					Thread.sleep(1000);
				}catch (InterruptedException ie) {}
			}
		}
		catch (IOException ioe)
		{
			System.err.println ("Socket error " + ioe);
		}
	}
}