Java Reference
In-Depth Information
Here are two example runs of this program:
c: \ > java TranslateAddress gluon.particle.kth.com
Address gluon.particle.kth.se = gluon.particle.kth.se/
130.237.34.133
Name of gluon.particle.kth.se = gluon.particle.kth.se
c: \ > java TranslateAddress 130.237.34.133
Address 130.237.34.133 = /130.237.34.133
Name of 130.237.34.133 = gluon.particle.kth.se
Note that the method getByName (String str) returns an instance of
InetAddress when given a host name. Then when the toString() method of
this InetAddress object is invoked by the string concatenation, it displays the
HostName/IP - Address pair. However, when given an IP address, the result-
ing InetAddress object does not show the host name. Instead, you can use the
getHostName() method to obtain the host name.
13.7 Sockets
Sockets provide connections between applications that allow streams of data
to flow. Sockets in Java are straightforward to set up. The package java.net
provides two kinds of socket classes:
1. Socket - provides a connection-oriented service that behaves like telnet or ftp. The
connection remains active, even with no communications occurring, until explicitly
broken.
2. DatagramSocket -involves the following:
(a) connectionless protocol
(b) transfer of datagram (i.e. UDP) packets
(c) no fixed connection
(d) packets can arrive out of order
(e) no guarantee a packet will arrive.
We discuss sockets further in Chapters 14 and 15. The demonstration program
below illustrates how to use a socket connection to run the whois internet operation
[2]. The whois service returns information about a given domain name. The
registry site whois.internic.net provides this service.
The code snippet below shows how to create an instance of the Socket class
that connects to port 43 at host name whois.internic.net .Anoutput stream
is obtained from the socket and a PrintWriter wrapped around it. This is then
used to send the address of interest to the whois service.
Similarly, an input stream is obtained from the socket and wrapped first
with an InputStreamReader and then a BufferedReader so we can use
readLine() to obtain a whole line of text at one time from the whois output.
Yo u can enter other domain names in the text field.
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