Protocol Handlers

When we call the URL.openConnection() method, the java.net package uses the

default URLStreamHandlerFactory to get a
default URLStreamHandler to open a
default URLConnection.

We can install our own stream handler factory to get first crack at any URL.

If we want to handle the specified protocol,

we return our own URLStreamHandler
otherwise we return null

and java.net will use the default factory.

public class HelpBrowser {
    ...
    URL.setURLStreamHandlerFactory(new KahunaURLStreamHandlerFactory());
    ...
}

class KahunaURLStreamHandlerFactory implements URLStreamHandlerFactory {
    public URLStreamHandler createURLStreamHandler(String protocol) {
        if (protocol.equalsIgnoreCase("kahuna")) {
            return new KahunaURLStreamHandler();
        } else {
            return null;
        }
    }
}

class KahunaURLStreamHandler extends URLStreamHandler {
    protected URLConnection openConnection(URL url) throws IOException {
        return new KahunaURLConnection(url);
    }
}

class KahunaURLConnection extends URLConnection {
    public InputStream getInputStream() throws IOException {
        String page = KahunaServer.getPage(url);
        return new ByteArrayInputStream(page.getBytes());
    }

    public void connect() throws IOException {}
    public String getContentType() { return "text/html"; }
}