correctly printstacktrace of servlet exception

Question

so i am using a filter to catch servlet exception (because we are using a mix of jsf/plain servlets)

when catching the ServletException and calling printstacktrace most of the information is lost.

the "true" root exception seems to be hidden behind the "funny" expression

((ServletException) e.getRootCause().getCause()).getRootCause().getCause().getCause().getCause()

this is clearly not the way to do it.

is the an easy way to print the "full" information of such an exception. can someone explain me why the exception is wrapped this way?

Answer 1

That is called exception chaining. By wrapping an exception in a different exception you can let exceptions bubble up the stack without having your main application classes to worry about some low-level exceptions.

Example:

public void doStuff() throws StuffException {
    try {
        doDatabaseStuff();
    } catch (DatabaseException de1) {
        throw new StuffException("Could not do stuff in the database.", de1);
    }
}

This way your application only has to handle StuffException but it can get to the underlying DatabaseException if it really needs to.

To get to the bottom-most (and all other) exception(s) of an exception you caught you can iterator over its root causes:

    ...
} catch (SomeException se1) {
    Throwable t = se1;
    logger.log(Level.WARNING, "Top exception", se1);
    while (t.getCause() != null) {
        t = t.getCause();
        logger.log(Level.WARNING, "Nested exception", t);
    }
    // now t contains the root cause
}

Answer 2

Take a look at the ExceptionUtils class from commons-lang. It contains several useful methods for printing the entire chain of exceptions.

Answer 3

after i had a look at ExceptionUtils, this solved the problem!

    final StringWriter stacktrace = new StringWriter();
 ExceptionUtils.printRootCauseStackTrace(throwable,new PrintWriter(stacktrace));
 msg.append(stacktrace.getBuffer());

this prints out the full stacktrace with every piece of information that is relevant.