Wrong catch block is reach

Question

Hi,
I encounter a strange behaviour in exception handling.
My web app can generate pdf files, and download them. If client closes its browser window, a ClientAbortException is thrown (which is expected behaviour, I guess.)
However, I can't catch it correctly. Here is my code:
try {
    // code for generating PDF and downloading it through response output stream.
catch(ClientAbortException caEx) {
    // No specific error handling required
    logger.info("Request aborted by client ["+caEx.getClass()+"] ["+caEx.getMessage()+"]", caEx);
    return "PDF_ERROR";
catch(Exception ex) {
    // A problem occured (TODO notify administrator)
    logger.info("PDF generation failed ["+ex.getClass()+"] ["+ex.getMessage()+"]", ex);
    return "PDF_ERROR";
}The problem is that even in case of ClientAbortException, the exception is caught by the second catch block, and log is:
PDF generation failed [class org.apache.catalina.connector.ClientAbortException] [null]
As you can see, Class name is the same. I tried debugging by adding the following logs in the second catch block:logger.info("instanceof ? "+ (ex instanceof ClientAbortException));
logger.info("class ? "+ (ex.getClass() == ClientAbortException.class));But both logged false.
Could someone explain why it can happen?

Answer 1

1) The fully qualified name of ClientAbortException from your class is indeed org.apache.catalina.connector.ClientAbortException. i.e., you are not importing some other ClientAbortException (that lives in a different package). You may want to print out exact class name by ClientAbortException.class.getName() or change the catch block as
catch (org.apache.catalina.connector.ClientAbortException caEx)
just to be sure.
2) If you get the situation even after verifying the fully qualified class name, then you may want to check whether these are loaded by the same loader or not. You may add the following lines:
logger.info("name equals? "+ (ex.getClass().getName().equals(ClientAbortException.class.getName());
logger.info("same loader ? "+ (ex.getClass().getClassLoader() == ClientAbortException.class.getClassLoader()));
if you get true and false respectively, then the what is seen is correct -- a class uniquely identified by fully qualified class name and the class loader that loaded it.