Java Reference
In-Depth Information
class can access sites that use HTTP authentication, although you'll of course need to
tell it which username and password to use.
Supporting sites that use nonstandard, cookie-based authentication is more challeng‐
ing, not least because this varies a lot from one site to another. Implementing cookie
authentication is hard short of implementing a complete web browser with full HTML
forms and cookie support; we'll discuss Java's cookie support in
Chapter 7
. Accessing
sites protected by standard HTTP authentication is much easier.
The Authenticator Class
The
java.net
package includes an
Authenticator
class you can use to provide a user‐
name and password for sites that protect themselves using HTTP authentication:
public
abstract
class
Authenticator
extends
Object
Since
Authenticator
is an abstract class, you must subclass it. Different subclasses may
retrieve the information in different ways. For example, a character mode program
might just ask the user to type the username and password on
System.in
. A GUI pro‐
gram would likely put up a dialog box like the one shown in
Figure 5-2
. An automated
robot might read the username out of an encrypted file.
Figure 5-2. An authentication dialog
To make the
URL
class use the subclass, install it as the default authenticator by passing
it to the static
Authenticator.setDefault()
method:
public
static
void
setDefault
(
Authenticator
a
)
For example, if you've written an
Authenticator
subclass named
DialogAuthentica
tor
, you'd install it like this:
Authenticator
.
setDefault
(
new
DialogAuthenticator
());
You only need to do this once. From this point forward, when the
URL
class needs a
username and password, it will ask the
DialogAuthenticator
using the static
Authen
ticator.requestPasswordAuthentication()
method:
public
static
PasswordAuthentication
requestPasswordAuthentication
(
InetAddress
address
,
int
port
,
String
protocol
,
String
prompt
,
String
scheme
)
throws
SecurityException
