daytimeudpclient.java

来自「apache推出的net包」· Java 代码 · 共 81 行

/*
 * Copyright 2001-2005 The Apache Software Foundation
 *
 * Licensed 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;

import java.io.IOException;
import java.net.DatagramPacket;
import java.net.InetAddress;

/***
 * The DaytimeUDPClient class is a UDP implementation of a client for the
 * Daytime protocol described in RFC 867.  To use the class, merely
 * open a local datagram socket with
 * {@link org.apache.commons.net.DatagramSocketClient#open  open }
 * and call {@link #getTime  getTime } to retrieve the daytime
 * string, then
 * call {@link org.apache.commons.net.DatagramSocketClient#close  close }
 * to close the connection properly.  Unlike
 * {@link org.apache.commons.net.DaytimeTCPClient},
 * successive calls to {@link #getTime  getTime } are permitted
 * without re-establishing a connection.  That is because UDP is a
 * connectionless protocol and the Daytime protocol is stateless.
 * <p>
 * <p>
 * @author Daniel F. Savarese
 * @see DaytimeTCPClient
 ***/

public final class DaytimeUDPClient extends DatagramSocketClient
{
    /*** The default daytime port.  It is set to 13 according to RFC 867. ***/
    public static final int DEFAULT_PORT = 13;

    private byte[] __dummyData = new byte[1];
    // Received dates should be less than 256 bytes
    private byte[] __timeData = new byte[256];

    /***
     * Retrieves the time string from the specified server and port and
     * returns it.
     * <p>
     * @param host The address of the server.
     * @param port The port of the service.
     * @return The time string.
     * @exception IOException If an error occurs while retrieving the time.
     ***/
    public String getTime(InetAddress host, int port) throws IOException
    {
        DatagramPacket sendPacket, receivePacket;

        sendPacket =
            new DatagramPacket(__dummyData, __dummyData.length, host, port);
        receivePacket = new DatagramPacket(__timeData, __timeData.length);

        _socket_.send(sendPacket);
        _socket_.receive(receivePacket);

        return new String(receivePacket.getData(), 0, receivePacket.getLength());
    }

    /*** Same as <code>getTime(host, DaytimeUDPClient.DEFAULT_PORT);</code> ***/
    public String getTime(InetAddress host) throws IOException
    {
        return getTime(host, DEFAULT_PORT);
    }

}