Head First EJB

Warning! RemoteException is checked, but not expected!

Normally when we think of expected vs. unexpected exceptions, we map it to checked vs. unchecked exceptions. A FileIOException is expected. A NullPointerException is not. Any direct subclass of Exception is expected. A subclass of RuntimeException is not. A checked exception must be handled. An unchecked exception usually won’t be.

But there’s one big exception to the whole exceptions and expectations thing—java.rmi.RemoteException.

RemoteException is a checked exception, of course, so the client is forced to acknowledge a RemoteException by handling it with a try/catch. But unlike the other checked exceptions a client sees in a bean’s interface, RemoteException is still considered unexpected. OK, not exactly unexpected... but unexpected.

Application exceptions are always compiler-checked exceptions, except for RemoteException.

Think of RemoteException as “a runtime exception on the server”, even though RemoteException is a checked exception to the client.

In other words, a remote client must EXPECT that the server can throw something UNEXPECTED.

From the client’s point of view, think of RemoteException a kind of runtime exception on the remote part of the application. Because that’s often what it means. A NullPointerException on the server means a RemoteException to the client. A DivideByZeroException on the server means a RemoteException to the client. A ClassCastException on the server means a RemoteException to the client. Those ...