Question

There’s a common problem I’ve come across a few times when logging exceptions in Java. There seem to be various different types to deal with. E.g. some wrap other exceptions and some don’t have a message at all – only a type.

Most code I’ve seen logs an exception by using either getMessage() or toString(). But these methods don’t always capture all the information needed to pinpoint the problem – other methods such as getCause() and getStackTrace() sometimes provide additional info.

For example, the exception I’m looking at right now in my Eclipse Inspect window is an InvocationTargetException. The exception itself has no cause, no message, no stacktrace … but the target from getCause() is InvalidUseOfMatchersException, with these details populated.

So my question is: Given an exception of any type as an input, please provide a single method that will output a nicely formatted string containing all relevant information about the Exception (e.g. possibly recursively calling getCause() amongst other things?) Before posting, I was nearly going to have a stab at it myself but really don’t want to reinvent the wheel – surely such a thing must have been done many times before…?

Answer 1

The java.util.logging package is standard in Java SE. Its Logger includes an overloaded log method that accepts Throwable objects.
It will log stacktraces of exceptions and their cause for you.

For example:

import java.util.logging.Level;
import java.util.logging.Logger;

[...]

Logger logger = Logger.getAnonymousLogger();
Exception e1 = new Exception();
Exception e2 = new Exception(e1);
logger.log(Level.SEVERE, "an exception was thrown", e2);

Will log:

SEVERE: an exception was thrown
java.lang.Exception: java.lang.Exception
    at LogStacktrace.main(LogStacktrace.java:21)
Caused by: java.lang.Exception
    at LogStacktrace.main(LogStacktrace.java:20)

Internally, this does exactly what @philipp-wendler suggests, by the way.
See the source code for SimpleFormatter.java. This is just a higher level interface.