DayTimeServer.java
package net.udp.daytime;
import java.net.*;
import java.io.*;
public abstract class DayTimeServer extends Thread {
private int bufferSize;
protected DatagramSocket ds;
public DayTimeServer(int port, int bufferSize) throws SocketException {
this.bufferSize = bufferSize;
this.ds = new DatagramSocket(port);
}
public DayTimeServer(int port) throws SocketException {
this(port, 8192);
}
public void run() {
byte[] buffer = new byte[bufferSize];
while (true) {
DatagramPacket incoming = new DatagramPacket(buffer, buffer.length);
try {
ds.receive(incoming);
this.respond(incoming);
} catch (IOException e) {
System.err.println(e);
}
}
}
public abstract void respond(DatagramPacket request);
}
DayTimeClient.java
package net.udp.daytime;
import java.net.InetAddress;
import java.util.Date;
public class DayTimeClient {
public final static int DEFAULT_PORT = 37;
public final static String DEFAULT_HOST = "localhost";
public static void main(String[] args) {
InetAddress host;
int port = DEFAULT_PORT;
try {
if (args.length > 0) {
host = InetAddress.getByName(args[0]);
} else {
host = InetAddress.getByName(DEFAULT_HOST);
}
} catch (Exception e) {
System.out.println("Usage: java UDPTimeClient host port");
return;
}
if (args.length > 1) {
try {
port = Integer.parseInt(args[1]);
if (port <= 0 || port > 65535)
port = DEFAULT_PORT;
;
} catch (Exception e) {
}
}
try {
UDPPoke poker = new UDPPoke(host, port);
byte[] response = poker.poke();
if (response == null) {
System.out.println("No response within allotted time");
return;
} else if (response.length != 4) {
System.out.println("Unrecognized response format");
return;
}
// The time protocol sets the epoch at 1900,
// the java Date class at 1970. This number
// converts between them.
long differenceBetweenEpochs = 2208988800L;
long secondsSince1900 = 0;
for (int i = 0; i < 4; i++) {
secondsSince1900 = (secondsSince1900 << 8) | (response[i] & 0x000000FF);
}
long secondsSince1970 = secondsSince1900 - differenceBetweenEpochs;
long msSince1970 = secondsSince1970 * 1000;
Date time = new Date(msSince1970);
System.out.println(time);
} catch (Exception e) {
System.err.println(e);
e.printStackTrace();
}
}
}
UDPPoke.java
import java.net.*;
import java.io.*;
public class UDPPoke {
private int bufferSize;
private DatagramSocket ds;
private DatagramPacket outgoing;
public UDPPoke(InetAddress host, int port, int bufferSize, int timeout) throws SocketException {
outgoing = new DatagramPacket(new byte[1], 1, host, port);
this.bufferSize = bufferSize;
ds = new DatagramSocket(0);
ds.connect(host, port);
ds.setSoTimeout(timeout);
}
public UDPPoke(InetAddress host, int port, int bufferSize) throws SocketException {
this(host, port, bufferSize, 30000);
}
public UDPPoke(InetAddress host, int port) throws SocketException {
this(host, port, 8192, 30000);
}
public byte[] poke() throws IOException {
byte[] response = null;
try {
ds.send(outgoing);
DatagramPacket incoming = new DatagramPacket(new byte[bufferSize], bufferSize);
ds.receive(incoming);
int numBytes = incoming.getLength();
response = new byte[numBytes];
System.arraycopy(incoming.getData(), 0, response, 0, numBytes);
} catch (IOException e) {
}
return response;
}
}
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