Java tutorial
/* * Licensed to the Apache Software Foundation (ASF) under one or more * contributor license agreements. See the NOTICE file distributed with * this work for additional information regarding copyright ownership. * The ASF licenses this file to You under the Apache License, Version 2.0 * (the "License"); you may not use this file except in compliance with * the License. You may obtain a copy of the License at * * http://www.apache.org/licenses/LICENSE-2.0 * * Unless required by applicable law or agreed to in writing, software * distributed under the License is distributed on an "AS IS" BASIS, * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. * See the License for the specific language governing permissions and * limitations under the License. */ package org.apache.commons.net.chargen; import java.io.IOException; import java.net.DatagramPacket; import java.net.InetAddress; import org.apache.commons.net.DatagramSocketClient; /*** * The CharGenUDPClient class is a UDP implementation of a client for the * character generator protocol described in RFC 864. It can also be * used for Systat (RFC 866), Quote of the Day (RFC 865), and netstat * (port 15). All of these protocols involve sending a datagram to the * appropriate port, and reading data contained in one or more reply * datagrams. The chargen and quote of the day protocols only send * one reply datagram containing 512 bytes or less of data. The other * protocols may reply with more than one datagram, in which case you * must wait for a timeout to determine that all reply datagrams have * been sent. * <p> * To use the CharGenUDPClient class, just open a local UDP port * with {@link org.apache.commons.net.DatagramSocketClient#open open } * and call {@link #send send } to send the datagram that will * initiate the data reply. For chargen or quote of the day, just * call {@link #receive receive }, and you're done. For netstat and * systat, call receive in a while loop, and catch a SocketException and * InterruptedIOException to detect a timeout (don't forget to set the * timeout duration beforehand). Don't forget to call * {@link org.apache.commons.net.DatagramSocketClient#close close() } * to clean up properly. * <p> * <p> * @see CharGenTCPClient ***/ public final class CharGenUDPClient extends DatagramSocketClient { /*** The systat port value of 11 according to RFC 866. ***/ public static final int SYSTAT_PORT = 11; /*** The netstat port value of 19. ***/ public static final int NETSTAT_PORT = 15; /*** The quote of the day port value of 17 according to RFC 865. ***/ public static final int QUOTE_OF_DAY_PORT = 17; /*** The character generator port value of 19 according to RFC 864. ***/ public static final int CHARGEN_PORT = 19; /*** The default chargen port. It is set to 19 according to RFC 864. ***/ public static final int DEFAULT_PORT = 19; private final byte[] __receiveData; private final DatagramPacket __receivePacket; private final DatagramPacket __sendPacket; /*** * The default CharGenUDPClient constructor. It initializes some internal * data structures for sending and receiving the necessary datagrams for * the chargen and related protocols. ***/ public CharGenUDPClient() { // CharGen return packets have a maximum length of 512 __receiveData = new byte[512]; __receivePacket = new DatagramPacket(__receiveData, __receiveData.length); __sendPacket = new DatagramPacket(new byte[0], 0); } /*** * Sends the data initiation datagram. This data in the packet is ignored * by the server, and merely serves to signal that the server should send * its reply. * <p> * @param host The address of the server. * @param port The port of the service. * @exception IOException If an error occurs while sending the datagram. ***/ public void send(InetAddress host, int port) throws IOException { __sendPacket.setAddress(host); __sendPacket.setPort(port); _socket_.send(__sendPacket); } /*** Same as <code>send(host, CharGenUDPClient.DEFAULT_PORT);</code> ***/ public void send(InetAddress host) throws IOException { send(host, DEFAULT_PORT); } /*** * Receive the reply data from the server. This will always be 512 bytes * or less. Chargen and quote of the day only return one packet. Netstat * and systat require multiple calls to receive() with timeout detection. * <p> * @return The reply data from the server. * @exception IOException If an error occurs while receiving the datagram. ***/ public byte[] receive() throws IOException { int length; byte[] result; _socket_.receive(__receivePacket); result = new byte[length = __receivePacket.getLength()]; System.arraycopy(__receiveData, 0, result, 0, length); return result; } }