When the JMXMP connector client gets a failed connection, subsequent operations (after the first one that encountered the failure) get IllegalStateException with a message "the connection has been closed". This is clearly wrong. It is already a bit questionable to throw this exception if the connection was explicitly closed, but it is definitely wrong to throw it if the connection has failed.

This sometimes shows up with the unit test BrokenConnectionTest. In the test for removeNotificationListener, we set up a listener, break the connection, then remove the listener. Usually this correctly gets IOException for the attempt to remove the listener. Sometimes, though, the fetchNotifications thread happens to get the failure first, and it moves the connection state to FAILED. Then the removeNotificationListener gets IllegalStateException, with a trace like this:

java.lang.IllegalStateException: The connection has been closed.
at com.sun.jmx.remote.generic.SynchroMessageConnectionImpl.checkState(SynchroMessageConnectionImpl.java:555)
at com.sun.jmx.remote.generic.SynchroMessageConnectionImpl.sendWithReturn(SynchroMessageConnectionImpl.java:164)
at javax.management.remote.generic.ClientIntermediary.mBeanServerRequest(ClientIntermediary.java:954)
at javax.management.remote.generic.ClientIntermediary.mBeanServerRequest(ClientIntermediary.java:936)
at javax.management.remote.generic.ClientIntermediary.removeNotificationListener(ClientIntermediary.java:688)
at javax.management.remote.generic.GenericConnector$RemoteMBeanServerConnection.removeNotificationListener(GenericConnector.java:593)
at BrokenConnectionTest$4.operation(BrokenConnectionTest.java:153)
at BrokenConnectionTest$Operation.test(BrokenConnectionTest.java:95)
at BrokenConnectionTest.test(BrokenConnectionTest.java:449)
at BrokenConnectionTest.jmxmpTest(BrokenConnectionTest.java:592)
at BrokenConnectionTest.test(BrokenConnectionTest.java:64)
at BrokenConnectionTest.main(BrokenConnectionTest.java:41)