Java identify an Exception precisely

Question

In Java we can catch exceptions of a certain type:

try{ 
    // Code that does IO like download a file...
}catch(IOException ioe){
    ioe.printStackTrace();
    // handle ioe
}catch(SomeOtherException soe){
    // handle soe 
}

Now, there can by many causes to an Exception, in this case, the IOException can be:

java.io.IOException: Illegal character in path at index.....

from a specific library or some other like:

java.io.IOException: Stream closed ...

If something went wrong with a Stream

Now, my question is, how do I determine what kind of IOException happened?

How do I distinguish between a Stream closed and Illegal character in path at index...?

Of course I can just check the String of the exception message but I don't think it's the best way since the underlying library/implementation can change the message string.

EDIT:

e.getClass() in this case returns java.io.IOException for almost everything...

I guess the library throws their own IOException while discarding any original Exception.

Answer 1

The fact that the printStackTrace printed

java.io.IOException: Stream closed ...
//      ^^^^^^^^^^^

and

java.io.IOException: Illegal character in path at index.....
//      ^^^^^^^^^^^

means the Exception is of type IOException. There isn't a more specific subtype you can use here.

There is no way in this case. They decided to use the same Exception type for both (and more) of those reasons. You won't be able to distinguish them with different catch statements. You'll need to check their message.

If the Exception has a cause, you'll have to see if there's a distinguishing type and rethrow it. If you're lucky, you might be able to catch a more specific type of Exception.