For reference - r1634258 and r1360468 I was backporting a test for BZ 54928 from Tomcat 8 to Tomcat 7 and noted a difference in output. The code was: log.info("Exception caught " + e.getMessage()); In Tomcat 7 (7.0.56+) it resulted in "Exception caught null" while on Tomcat 8 (8.0.14+) it was "Exception caught Software caused connection abort: socket write error". When I changed the code to use e.toString() it became: in Tomcat 7: "Exception caught ClientAbortException: java.net.SocketException: Software caused connection abort: socket write error" in Tomcat 8: "Exception caught org.apache.catalina.connector.ClientAbortException: java.net.SocketException: Software caused connection abort: socket write error" The difference comes from r1360468. Essentially Tomcat 8 delegates processing to original implementations in java.lang.Throwable, while the old code in Tomcat 7 has its own implementation of getMessage() and toString(). There are two differences: a) The Throwable(Throwable cause) constructor in Java initializes message as cause.toString() while in ClientAbortException(Throwable) the message defaults to being null. b) Throwable.toString() uses the fully qualified name of a class, while ClientAbortException.toString() prints just "ClientAbortException".
Fixed in Tomcat 7 by r1634311 and will be in 7.0.57 onwards.