The recent JDK-8213942 fix adjusted the synchronization logic for the handlers Hashtable. A minor enhancement can be made to improve synchronization.

One thread may release at/around this section while another thread then clears the handlers table in setURLStreamHandlerFactory method :

1418 if (handler2 != null) {
1419 // The handler from the factory must be given more
1420 // importance. Discard the default handler that
1421 // this thread created.
1422 handler = handler2;
1423 }
1424 } ===========> HERE
1425
1426 // Insert this handler into the hashtable
1427 if (handler != null) {
1428 handlers.put(protocol, handler);
1429 }