log4j not printing the stacktrace for exceptions

Question

I am using log4j with tomcat. When I log exceptions in my JSPs, servlets:

private Logger _log = Logger.getLogger(this.getClass());
...
try{...} catch (Except         


        

Answer 1

I don't see anything wrong with your config, so try to upgrade log4j to a newer (not necessarily the latest) version.

Though not the problem in this case, you'd better make your loggers private static final

Answer 2

What you have posted should display the stack trace as stated in the javadoc.

Note that if you don't include a message (and just call logger.error(ex)) then the stack trace is not logged.

Answer 3

Like answered by @Luhar above, I struggled with same thing and finally this worked for me; Good thing about this approach is we don't have to tinker with system level settings like JVM, Log4J since we never know it may lead to new unexpected surprise !

try {

...
..

} catch (Exception er) {
        ByteArrayOutputStream os = new ByteArrayOutputStream();
        er.printStackTrace(new PrintStream(os));
        LOGGER.error(new String(os.toByteArray()));
        //LOGGER.error(er);
}

Answer 4

You can add these lines of code in your catch block.

catch (SQLException e) {
            CharArrayWriter cw = new CharArrayWriter();
            PrintWriter w = new PrintWriter(cw);
            e.printStackTrace(w);
            w.close();
            String trace = cw.toString();

    log.error("This is complete stacktrace", trace);
}

Answer 5

Actually, it's probably due to a hotspot optimization: after a certain number of the same exception being thrown it stops printing out trace. This can be turned off with a VM arg, see:

From http://www.oracle.com/technetwork/java/javase/relnotes-139183.html :

The compiler in the server VM now provides correct stack backtraces for all "cold" built-in exceptions. For performance purposes, when such an exception is thrown a few times, the method may be recompiled. After recompilation, the compiler may choose a faster tactic using preallocated exceptions that do not provide a stack trace. To disable completely the use of preallocated exceptions, use this new flag: -XX:-OmitStackTraceInFastThrow.

More here:

http://jawspeak.com/2010/05/26/hotspot-caused-exceptions-to-lose-their-stack-traces-in-production-and-the-fix/

Answer 6

Using your code sample:

private static final Logger _log = Logger.getLogger(MyClass.class);
...
try{...} catch (Exception e) {
    //Change
    //_log.error("Error refreshing all prices", e);

   //To
    _log.error("Error refreshing all prices", e.fillInStackTrace());
}

You'll see all the stack trace displayed.

PS. Make Logger a singleton...(check my declaration) just after declaring public class MyClass {