Moving toward bundles - OSGi in Action - page 214

URL handlers must be registered as OSG i services, which also means the handlers are
tied to their bundle lifecycle.

FIXING THE URL HANDLER ISSUE
Your first thought may be to try to disable the URL Handlers Service so it doesn't
install this factory. Unfortunately, there's no standard switch for this; but to disable it
in Felix, you set the felix.service.urlhandlers framework property to false . Turn-
ing off the global URL Handlers Service also has serious implications. It means no
bundle can contribute dynamic protocol handlers, which would break applications
that rely on the URL Handlers Service. It also won't fix this particular problem
because the jeditresource handler isn't visible to the default URL StreamHandler-
Factory when you run jEdit as a bundle. The JDK 's URL Handler factory uses
Class.forName() to search the application class path for valid handlers, but your
jeditresource handler is hidden from view inside the jEdit bundle class loader.
The solution is to register the jeditresource handler as a URLStreamHandler-
Service when the jEdit bundle is started and remove it when the bundle is stopped.
But how can you add OSG i-specific code without affecting classic jEdit users? Cast your
mind back to section 6.1.5, where we talked about using lifecycles to manage external
resources. This is exactly the sort of situation that requires a bundle activator, such as
the one shown next.

Listing 6.3 Bundle activator to manage the jeditresource handler

package org.gjt.sp.jedit;

import java.io.IOException;
import java.net.*;
import java.util.Properties;

import org.osgi.framework.*;
import org.osgi.service.url.*;

import org.gjt.sp.jedit.proto.jeditresource.Handler;

public class Activator implements BundleActivator {
private static class JEditResourceHandlerService
extends AbstractURLStreamHandlerService {
private Handler jEditResourceHandler = new Handler();

public URLConnection openConnection(URL url)
throws IOException {
return jEditResourceHandler.openConnection(url);
}
}

Delegates to
real handler

public void start(BundleContext context) {
Properties properties = new Properties();
properties.setProperty(URLConstants.URL_HANDLER_PROTOCOL,
"jeditresource");

Publishes URL
handler service

context.registerService(
URLStreamHandlerService.class.getName(),
new JEditResourceHandlerService(),