Catching an exception that is nested into another exception

Question

I want to catch an exception, that is nested into another exception. I\'m doing it currently this way:

} catch (RemoteAccessException e) {
    if (e != null          


        

Answer 1

I just solved a problem like this by writing a simple utility method, which will check the entire caused-by chain.

  /**
   * Recursive method to determine whether an Exception passed is, or has a cause, that is a
   * subclass or implementation of the Throwable provided.
   *
   * @param caught          The Throwable to check
   * @param isOfOrCausedBy  The Throwable Class to look for
   * @return  true if 'caught' is of type 'isOfOrCausedBy' or has a cause that this applies to.
   */
  private boolean isCausedBy(Throwable caught, Class isOfOrCausedBy) {
    if (caught == null) return false;
    else if (isOfOrCausedBy.isAssignableFrom(caught.getClass())) return true;
    else return isCausedBy(caught.getCause(), isOfOrCausedBy);
  }

When you use it, you would just create a list of if's from most specific Exception to least specific, with a fallback else-clause:

try {
  // Code to be executed
} catch (Exception e) {
  if (isCausedBy(e, MyException.class)) {
    // Handle MyException.class
  } else if (isCausedBy(e, AnotherException.class)) {
    // Handle AnotherException.class
  } else {
    throw new IllegalStateException("Error at calling service 'service'");
  }
}

Alternative/Addition per requests in comments

If you want to use a similar method to get the Exception object of the class you're looking for, you can use something like this:

  private boolean getCausedByOfType(Throwable caught, Class isOfOrCausedBy) {
    if (caught == null) return null;
    else if (isOfOrCausedBy.isAssignableFrom(caught.getClass())) return caught;
    else return getCausedByOfType(caught.getCause(), isOfOrCausedBy);
  }

This could be used in addition to isCausedBy() this way:

  if (isCausedBy(e, MyException.class)) {
    Throwable causedBy = getCausedBy(e, MyException.class);
    System.err.println(causedBy.getMessage());
  }

It can also used directly instead of isCausedBy(), although it's probably a matter of opinion whether this is more readable.

  Throwable causedBy;
  if ((causedBy = getCausedBy(e, IllegalAccessException.class)) != null) {
    System.err.println(causedBy.getMessage());
  }