Exception chaining in Java

If you catch and rethrow exceptions in Java, you probably know about exception chaining already: You simply give the exception you “wrap” as second argument to your Exception like this

try { … }
catch (Exception e) {
throw new CustomException(“something went wrong”, e);
}

and if you look at the stack trace of the newly thrown exception, the original one is listed as “Caused by:”. Now today I had the rather “usual” use case of cleanup up a failing action and the cleanup itself was able to throw as well. So I had two causing exceptions and I wanted to conserve both of them, including their complete cause chain, in a new exception. Consider the following example:

try { … }
catch (Exception e1) {
try { … }
catch (Exception e2) {
// how to transport e1 and e2 in a new exception here?!
}
throw e1;
}

My idea here was to somehow tack the exception chain of `e1` onto the exception chain of `e2`, but Java offered no solution for this. So I hunted for my own one:

public static class ChainedException extends Exception {
public ChainedException(String msg, Throwable cause) {
super(msg, cause);
}
public void appendRootCause(Throwable cause) {
Throwable parent = this;
while (parent.getCause() != null) {
parent = parent.getCause();
}
parent.initCause(cause);
}
}

Now I only had to base the exceptions I actually want to chain on `ChainedException` and was able to do this (in fact I based all of them on this class):

try { … }
catch (ChainedException e1) {
try { … }
catch (ChainedException e2) {
e2.appendRootCause(e1);
throw new ChainedException(“cleanup failed”, e2);
}
throw e1;
}

Try it out yourself – you’ll see the trace of `e1` at the bottom of the cause chain of `e2`. Quite nice, eh?