Timothy Ward created FELIX-5310:
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Summary: Felix HTTP Jetty WebSockets do not work out of the box
Key: FELIX-5310
URL: https://issues.apache.org/jira/browse/FELIX-5310
Project: Felix
Issue Type: Bug
Components: HTTP Service
Affects Versions: http.jetty-3.2.0
Reporter: Timothy Ward
I have encountered two significant problems when trying to use the Jetty
WebSocketServlet with the Jetty based Felix HTTP service whiteboard. Both
problems occur in the init method of my servlet.
1. I have to set the TCCL for the Jetty Web Socket implementation to be able
to find its own internal implementation of Websockets (specifically
org.eclipse.jetty.websocket.server.WebSocketServerFactory). This is really
stupid, as the TCCL I have to use is the Felix HTTP Jetty bundle's class loader!
2. The Jetty Web Socket implementation does one (and only one) check to check
that it's running on Jetty. It looks as though the only reason for this is to
get hold of an Executor which is available via a getter. This check involves
trying to establish the Jetty Context by casting the ServletContext to a Jetty
internal type. This does not work as the HTTP Whiteboard wrappers the
ServletContext. I can work around this by delaying initialisation to the first
request so that there is a context to get hold of, but this also sucks :(
In summary, my servlet has to look like this, most of which should not be
necessary!
public class EchoServlet extends WebSocketServlet {
private static final Logger LOGGER =
LoggerFactory.getLogger(EchoServlet.class);
private final AtomicBoolean firstCall = new AtomicBoolean(true);
private final CountDownLatch initBarrier = new CountDownLatch(1);
@Override
public void init() throws ServletException {
LOGGER.info("The Echo servlet has been initialized, but we delay
initialization until the first request so that a Jetty Context is available");
}
@Override
public void service(ServletRequest arg0, ServletResponse arg1) throws
ServletException, IOException {
if(firstCall.compareAndSet(true, false)) {
try {
delayedInit();
} finally {
initBarrier.countDown();
}
} else {
try {
initBarrier.await();
} catch (InterruptedException e) {
throw new ServletException("Timed out waiting for
initialisation", e);
}
}
super.service(arg0, arg1);
}
private void delayedInit() throws ServletException {
// Overide the TCCL so that the internal factory can be found
// Jetty tries to use ServiceLoader, and their fallback is to
// use TCCL, it would be better if we could provide a loader...
Thread currentThread = Thread.currentThread();
ClassLoader tccl = currentThread.getContextClassLoader();
currentThread.setContextClassLoader(WebSocketServlet.class.getClassLoader());
try {
super.init();
} finally {
currentThread.setContextClassLoader(tccl);
}
}
@Override
public void configure(WebSocketServletFactory wsf) {
wsf.setCreator((req,res) -> new WebSocketAdaptor() {
public void onWebSocketText(String message) {
getRemote().sendStringByFuture("Echo: " + message);
}
});
}
}
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