<Swing Dev> jdk6 and jdk7: wrong class cast in sun.print.IPPPrintService (in Solaris classes)

[Nico R.]

Hello!

In sun.print.IPPPrintService.getIPPConnection(URL), there is a bug with
class casting: see


<URL:http://hg.openjdk.java.net/jdk6/jdk6/jdk/file/5672a2be515a/src/solaris/classes/sun/print/IPPPrintService.java>,
lines 1556–1565 for JDK 6,

and


<URL:http://hg.openjdk.java.net/jdk7/swing/jdk/file/d449b91c56b6/src/solaris/classes/sun/print/IPPPrintService.java>,
lines 1563–1572 for JDK 7.

The buggy code is:

    public static HttpURLConnection getIPPConnection(URL url) {
        HttpURLConnection connection;
        try {
            connection = (HttpURLConnection)url.openConnection();
        } catch (java.io.IOException ioe) {
            return null;
        }
        if (!(connection instanceof HttpURLConnection)) {
            return null;
        }

If the call to openConnection returns a FileURLConnection (as it does on
my system), that cannot be cast to an HttpURLConnection. The instanceof
check happens too late in the code.

What to do: either
  * catch a ClassCastException and return null from the catch block, or
  * use a variable of type URLConnection to store the result from
openConnection(), and cast it to HttpURLConnection /after/ the block
with the instanceof check.

The problem occurs, because there are URLs like "file:/dev/null" in the
list or URLs to try. They are retrieved from
sun.print.CUPSPrinter.getAllPrinters() via
sun.print.UnixPrintServiceLookup.refreshServices().

I assume this happens for printers that were auto-detected (e.g. via
ZeroConf etc.) some time ago, but are not accessible at the moment), but
I am not sure about that.

Perhaps the CUPS system is improperly configured, but this should not
cause Java applications to throw ClassCastExceptions.

Regards
-- 
Nico