I have a custom exception class (BaseException) with an "errorCode" attribute, and overridden the toString method to return errorCode + Exception.getMessage

log4j is simply using toString(), which logs the exceptions as required.

ThrowableProxyUtil.printFirstLine uses
buf.append(tp.getClassName()).append(": ").append(tp.getMessage());

In some cases, Exception.getMessage will return null, as my application will only return the error code to the caller.

Can logback provide an option to use toString instead of manually appending the class name and getMessage? or simply use toString?