如何在Java中捕获异常？

Question

I am getting following exception in my code and I want to catch the inner exception. Is it possible to catch that?

java.lang.RuntimeException: error
some stack trace
some stack trace
some stack trace
! Caused by: java.util.concurrent.TimeoutException: null
some stack trace
some stack trace
some stack trace

Lets say I have following code.

function abc() {
  try{
    xyz()
  } catch (TimeoutException e) {
     do stuff
  }
}

xyz() function is generating that exception. Would catching the TimeoutException like this work?

Answer 1

You can't do it directly. You have to catch the outer exception, check its getCause() to see if it's what you want, and then either handle that cause or re-throw the top-level exception.

(You could also technically re-throw just the inner one, but I would strongly discourage that; the stack trace will be very confusing, and it'll be harder to debug -- especially a year from now, when you've forgotten that you did that.)

Answer 2

No, you can't catch a RuntimeException with catch(TimeoutException e) .

However, you could do

} catch (RuntimeException e) {
  Throwable cause = e.getCause(); 
}

to get the cause.

Answer 3

You cannot directly catch a RuntimeException caused by a TimeoutException .

But you achieve it like this:

    try {
        xyz();
    } catch (RuntimeException e) {
        if (e.getCause() instanceof TimeoutException) {
            // handle TimeoutException
            doStuff();
        } else {
            // rethrow all exceptions with other causes
            throw e;
        }
    }