URLConnections - Java Network Programming - page 210

causes the URLConnection to disconnect should set this field to false. There are no such
methods in java.net.URLConnection , but some of its subclasses, such as
java.net.HttpURLConnection , have disconnect() methods.
If you subclass URLConnection to write a protocol handler, you are responsible for set‐
ting connected to true when you are connected and resetting it to false when the
connection closes. Many methods in java.net.URLConnection read this variable to
determine what they can do. If it's set incorrectly, your program will have severe bugs
that are not easy to diagnose.
protected boolean allowUserInteraction
Some URLConnection s need to interact with a user. For example, a web browser may
need to ask for a username and password. However, many applications cannot assume
that a user is present to interact with it. For instance, a search engine robot is probably
running in the background without any user to provide a username and password. As
its name suggests, the allowUserInteraction field specifies whether user interaction
is allowed. It is false by default.
This variable is protected, but the public getAllowUserInteraction() method can read
its value and the public setAllowUserInteraction() method can change it:
public void setAllowUserInteraction ( boolean allowUserInteraction )
public boolean getAllowUserInteraction ()
The value true indicates that user interaction is allowed; false indicates that there is
no user interaction. The value may be read at any time but may be set only before the
URLConnection is connected. Calling setAllowUserInteraction() when the
URLConnection is connected throws an IllegalStateException .
For example, this code fragment opens a connection that could ask the user for au‐
thentication if it's required:
URL u = new URL ( "http://www.example.com/passwordProtectedPage.html" );
URLConnection uc = u . openConnection ();
uc . setAllowUserInteraction ( true );
InputStream in = uc . getInputStream ();
Java does not include a default GUI for asking the user for a username and password.
If the request is made from an applet, the browser's usual authentication dialog can be
relied on. In a standalone application, you first need to install an Authenticator , as
discussed in “Accessing Password-Protected Sites” on page 161 .
Figure 7-1 shows the dialog box that pops up when you try to access a password-
protected page. If you cancel this dialog, you'll get a 401 Authorization Required error
and whatever text the server sends to unauthorized users. However, if you refuse to send
authorization at all—which you can do by clicking OK, then answering No when asked