How to display stack trace on a caught exception?

Question

I have a generic function that prints exceptions (using log4j):

private void _showErrorMessage(Exception e) {
    log.error(e.getClass() + ": " +  e.getMessage() + ": " + e.getCause() + "\n" +  e.getStackTrace().toString());
}

Instead of seeing the stack trace I'm seeing:

[Ljava.lang.StackTraceElement;@49af7e68

How can I view the stack trace of the exception properly?

update

log.error(e) <- shows the error, but doesn't show stack trace

Answer 1

Throwable.getStackTrace returns an array of StackTraceElements, hence the toString method is returning a textual representation of the array itself.

In order to actually retrieve the stack trace information, one would have to go through each StackTraceElement to get more information.

Answer 2

Your logging framework should have the ability to log exceptions, so simply passing the exception to the proper .error(Object, Throwable) call should be enough:

• log4j can do it
• commons logging can do it
• java.util.logging can do it

If your logging framework can't do that, or you need the stack trace in a String for any other reason, then it becomes a bit harder. You'll have to create a PrintWriter wrapping a StringWriter and call .printStackTrace() on the Exception:

StringWriter sw = new StringWriter();
ex.printStackTrace(new PrintWriter(sw));
String stacktrace = sw.toString();

Answer 3

I'll use the ExceptionUtils#getFullStackTrace of jakarta commons lang

Answer 4

Have you tried?

private void _showErrorMessage(Exception e) {
    log.error("Hey! got an exception", e);
}

Answer 5

You could also look at the Guava libraries from Google.

Throwables.getStackTraceAsString(Throwable throwable)

Answer 6

The exact answer to your question is that you should call Log4J like this:

private void _showErrorMessage(Exception e) {
    log.error(e.getClass() + ": " +  e.getMessage() + ": " + e.getCause(), e);
}

Although I would dispense with the call to e.getCause() because the stacktrace will give that to you anyway, so:

private void _showErrorMessage(Exception e) {
    log.error(e.getClass() + ": " +  e.getMessage(), e);
}

ExceptionUtils is fine if you really need a string of the stacktrace, but since you are using Log4J, you lose a lot by not utilizing its built in exception handling.