Network Clients - Java - page 515

The time difference is the number of years multiplied by 365, plus the number of leap days
between the two dates (in the years 1904, 1908, . . . , 1968)—i.e., 19 days.

The integer that we read from the server is a C-language unsigned int . But Java doesn't
provide an unsigned integer type; normally when you need an unsigned number, you use the
next-larger integer type, which would be long . But Java also doesn't give us a method to
read an unsigned integer from a data stream. The DataInputStream method readInt()
reads Java-style signed integers. There are readUnsignedByte() methods and
readUnsignedShort() methods, but no readUnsignedInt() method. Accordingly, we syn-
thesize the ability to read an unsigned int (which must be stored in a long , or else you'd
lose the signed bit and be back where you started from) by reading unsigned bytes and reas-
sembling them using Java's bit-shifting operators:

At the end of the code, we use the new date/time API (see Chapter 6 ) to construct and print a
LocalDateTime object to show the current date and time on the local (client) machine:

$ java network.RDateClient dalai
Remote time is 3600895637
BASE_DIFF is 2208988800
Time diff == 1391906837
Time on dalai is Sat Feb 08 19:47:17 EST 2014
Local date/time = 2014-02-08T19:47:17.703
$

The name dalai is the hostname of one of my OpenBSD Unix computers. Looking at the out-
put, you can see that the server agrees within a second. So the date calculation code in
Example 13-6 is probably correct. This protocol is commonly known as rdate , so the client
code is called RDateClient .

Example 13-6. RDateClient.java
public

public class RDateClient {

/** The TCP port for the binary time service. */
public

class RDateClient

public static short TIME_PORT = 37 ;

/** Seconds between 1970, the time base for Date(long) and Time.
* Factors in leap years (up to 2100), hours, minutes, and seconds.
* Subtract 1 day for 1900, add in 1/2 day for 1969/1970.
*/
protected

static final final short

protected static static final final long long BASE_DAYS =

( long long )(( 1970 - 1900 )* 365 + ( 1970 - 1900 - 1 )/ 4 );

/* Seconds since 1970 */