Finding and Reporting Network Addresses
Problem
You want to look up a host’s address name or number, or get the address at the other end of a network connection.
Solution
Get an InetAddress object.
Discussion
The InetAddress object represents the Internet
address of a given computer or host. There are no public
constructors; you obtain an InetAddress by calling
the static byName( )
method, passing in either a hostname like www.darwinsys.com or a network address as a
string, like “1.23.45.67”. All the “lookup”
methods in this class can throw the checked exception
UnknownHostException, which must be caught or
declared on the calling method’s header. None of these methods
actually contacts the remote host, so they do not throw the other
exceptions related to network connections.
The method getHostAddress( )
gives
you the numeric IP address (as a string) corresponding to the
InetAddress. The inverse is getHostName( )
, which reports the name of the
InetAddress. This can be used to print the address
of a host given its name, or vice versa:
// From InetAddrDemo.java
String ipNumber = "123.45.67.89";
String hostName = "www.darwinsys.com";
System.out.println(hostName + "'s address is " +
InetAddress.byName(hostName).getHostAddress( ));
System.out.println(ipNumber + "'s name is " +
InetAddress.byName(ipNumber).getHostName( ));You can also get an InetAddress from a
Socket by calling its getInetAddress( )
method. You can construct a
Socket using an InetAddress instead of a hostname string. ...