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16 package org.apache.commons.net;
17
18 import java.io.IOException;
19 import java.net.DatagramPacket;
20 import java.net.InetAddress;
21 import java.util.Date;
22
23 /***
24 * The TimeUDPClient class is a UDP implementation of a client for the
25 * Time protocol described in RFC 868. To use the class, merely
26 * open a local datagram socket with
27 * {@link org.apache.commons.net.DatagramSocketClient#open open }
28 * and call {@link #getTime getTime } or
29 * {@link #getTime getDate } to retrieve the time. Then call
30 * {@link org.apache.commons.net.DatagramSocketClient#close close }
31 * to close the connection properly. Unlike
32 * {@link org.apache.commons.net.TimeTCPClient},
33 * successive calls to {@link #getTime getTime } or
34 * {@link #getDate getDate } are permitted
35 * without re-establishing a connection. That is because UDP is a
36 * connectionless protocol and the Time protocol is stateless.
37 * <p>
38 * <p>
39 * @author Daniel F. Savarese
40 * @see TimeTCPClient
41 ***/
42
43 public final class TimeUDPClient extends DatagramSocketClient
44 {
45 /*** The default time port. It is set to 37 according to RFC 868. ***/
46 public static final int DEFAULT_PORT = 37;
47
48 /***
49 * The number of seconds between 00:00 1 January 1900 and
50 * 00:00 1 January 1970. This value can be useful for converting
51 * time values to other formats.
52 ***/
53 public static final long SECONDS_1900_TO_1970 = 2208988800L;
54
55 private byte[] __dummyData = new byte[1];
56 private byte[] __timeData = new byte[4];
57
58 /***
59 * Retrieves the time from the specified server and port and
60 * returns it. The time is the number of seconds since
61 * 00:00 (midnight) 1 January 1900 GMT, as specified by RFC 868.
62 * This method reads the raw 32-bit big-endian
63 * unsigned integer from the server, converts it to a Java long, and
64 * returns the value.
65 * <p>
66 * @param host The address of the server.
67 * @param port The port of the service.
68 * @return The time value retrieved from the server.
69 * @exception IOException If an error occurs while retrieving the time.
70 ***/
71 public long getTime(InetAddress host, int port) throws IOException
72 {
73 long time;
74 DatagramPacket sendPacket, receivePacket;
75
76 sendPacket =
77 new DatagramPacket(__dummyData, __dummyData.length, host, port);
78 receivePacket = new DatagramPacket(__timeData, __timeData.length);
79
80 _socket_.send(sendPacket);
81 _socket_.receive(receivePacket);
82
83 time = 0L;
84 time |= (((__timeData[0] & 0xff) << 24) & 0xffffffffL);
85 time |= (((__timeData[1] & 0xff) << 16) & 0xffffffffL);
86 time |= (((__timeData[2] & 0xff) << 8) & 0xffffffffL);
87 time |= ((__timeData[3] & 0xff) & 0xffffffffL);
88
89 return time;
90 }
91
92 /*** Same as <code> getTime(host, DEFAULT_PORT); </code> ***/
93 public long getTime(InetAddress host) throws IOException
94 {
95 return getTime(host, DEFAULT_PORT);
96 }
97
98
99 /***
100 * Retrieves the time from the server and returns a Java Date
101 * containing the time converted to the local timezone.
102 * <p>
103 * @param host The address of the server.
104 * @param port The port of the service.
105 * @return A Date value containing the time retrieved from the server
106 * converted to the local timezone.
107 * @exception IOException If an error occurs while fetching the time.
108 ***/
109 public Date getDate(InetAddress host, int port) throws IOException
110 {
111 return new Date((getTime(host, port) - SECONDS_1900_TO_1970)*1000L);
112 }
113
114
115 /*** Same as <code> getTime(host, DEFAULT_PORT); </code> ***/
116 public Date getDate(InetAddress host) throws IOException
117 {
118 return new Date((getTime(host, DEFAULT_PORT) -
119 SECONDS_1900_TO_1970)*1000L);
120 }
121
122 }
123