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Java > Open Source Codes > org > apache > commons > net > ntp > NTPUDPClient


1 package org.apache.commons.net.ntp;
2 /*
3  * Copyright 2001-2005 The Apache Software Foundation
4  *
5  * Licensed under the Apache License, Version 2.0 (the "License");
6  * you may not use this file except in compliance with the License.
7  * You may obtain a copy of the License at
8  *
9  * http://www.apache.org/licenses/LICENSE-2.0
10  *
11  * Unless required by applicable law or agreed to in writing, software
12  * distributed under the License is distributed on an "AS IS" BASIS,
13  * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
14  * See the License for the specific language governing permissions and
15  * limitations under the License.
16  */
17
18 import java.io.IOException JavaDoc;
19 import java.net.DatagramPacket JavaDoc;
20 import java.net.InetAddress JavaDoc;
21 import org.apache.commons.net.DatagramSocketClient;
22
23 /***
24  * The NTPUDPClient class is a UDP implementation of a client for the
25  * Network Time Protocol (NTP) described in RFC 1305 as well as the
26  * Simple Network Time Protocol (SNTP) in RFC-2030. To use the class,
27  * merely open a local datagram socket with <a HREF="#open"> open </a>
28  * and call <a HREF="#getTime"> getTime </a> to retrieve the time. Then call
29  * <a HREF="org.apache.commons.net.DatagramSocketClient.html#close"> close </a>
30  * to close the connection properly.
31  * Successive calls to <a HREF="#getTime"> getTime </a> are permitted
32  * without re-establishing a connection. That is because UDP is a
33  * connectionless protocol and the Network Time Protocol is stateless.
34  *
35  * @author Jason Mathews, MITRE Corp
36  * @version $Revision: 165675 $ $Date: 2005-05-02 15:09:55 -0500 (Mon, 02 May 2005) $
37  ***/
38
39 public final class NTPUDPClient extends DatagramSocketClient
40 {
41     /*** The default NTP port. It is set to 123 according to RFC 1305. ***/
42     public static final int DEFAULT_PORT = 123;
43
44     private int _version = NtpV3Packet.VERSION_3;
45
46     /***
47      * Retrieves the time information from the specified server and port and
48      * returns it. The time is the number of miliiseconds since
49      * 00:00 (midnight) 1 January 1900 UTC, as specified by RFC 1305.
50      * This method reads the raw NTP packet and constructs a <i>TimeInfo</i>
51      * object that allows access to all the fields of the NTP message header.
52      * <p>
53      * @param host The address of the server.
54      * @param port The port of the service.
55      * @return The time value retrieved from the server.
56      * @exception IOException If an error occurs while retrieving the time.
57      ***/
58     public TimeInfo getTime(InetAddress JavaDoc host, int port) throws IOException JavaDoc
59     {
60         // if not connected then open to next available UDP port
61 if (!isOpen())
62         {
63             open();
64         }
65
66         NtpV3Packet message = new NtpV3Impl();
67         message.setMode(NtpV3Packet.MODE_CLIENT);
68         message.setVersion(_version);
69         DatagramPacket JavaDoc sendPacket = message.getDatagramPacket();
70         sendPacket.setAddress(host);
71         sendPacket.setPort(port);
72
73         NtpV3Packet recMessage = new NtpV3Impl();
74         DatagramPacket JavaDoc receivePacket = recMessage.getDatagramPacket();
75
76         /*
77          * Must minimize the time between getting the current time,
78          * timestamping the packet, and sending it out which
79          * introduces an error in the delay time.
80          * No extraneous logging and initializations here !!!
81          */
82         TimeStamp now = TimeStamp.getCurrentTime();
83
84         // Note that if you do not set the transmit time field then originating time
85 // in server response is all 0's which is "Thu Feb 07 01:28:16 EST 2036".
86 message.setTransmitTime(now);
87
88         _socket_.send(sendPacket);
89         _socket_.receive(receivePacket);
90
91         long returnTime = System.currentTimeMillis();
92         // create TimeInfo message container but don't pre-compute the details yet
93 TimeInfo info = new TimeInfo(recMessage, returnTime, false);
94
95         return info;
96     }
97
98     /***
99      * Retrieves the time information from the specified server on the
100      * default NTP port and returns it. The time is the number of miliiseconds
101      * since 00:00 (midnight) 1 January 1900 UTC, as specified by RFC 1305.
102      * This method reads the raw NTP packet and constructs a <i>TimeInfo</i>
103      * object that allows access to all the fields of the NTP message header.
104      * <p>
105      * @param host The address of the server.
106      * @return The time value retrieved from the server.
107      * @exception IOException If an error occurs while retrieving the time.
108      ***/
109     public TimeInfo getTime(InetAddress JavaDoc host) throws IOException JavaDoc
110     {
111         return getTime(host, NtpV3Packet.NTP_PORT);
112     }
113
114     /***
115      * Returns the NTP protocol version number that client sets on request packet
116      * that is sent to remote host (e.g. 3=NTP v3, 4=NTP v4, etc.)
117      *
118      * @return the NTP protocol version number that client sets on request packet.
119      * @see #setVersion(int)
120      ***/
121     public int getVersion()
122     {
123         return _version;
124     }
125
126     /***
127      * Sets the NTP protocol version number that client sets on request packet
128      * communicate with remote host.
129      *
130      * @param version the NTP protocol version number
131      ***/
132     public void setVersion(int version)
133     {
134         _version = version;
135     }
136
137 }
138
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