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 (Exception e) {
    _log.error("Error refreshing all prices", e);
}

I only get the first line of the exception, without a stacktrace.

17-Feb 17:37:45 ERROR AutoContrib:175 - Exception while publishing csv file: java.lang.ArrayIndexOutOfBoundsException

Not very helpful at all!

My log4j.properties file (/tomcat/common/classes/log4j.properties) looks like this:

log4j.appender.stdout=org.apache.log4j.ConsoleAppender
log4j.appender.stdout.Target=System.out
log4j.appender.stdout.layout=org.apache.log4j.PatternLayout
log4j.appender.stdout.layout.ConversionPattern=%d{dd-MMM HH:mm:ss} %5p %c{1}:%L - %m%n
log4j.appender.stdout.threshold=info

log4j.appender.file=org.apache.log4j.RollingFileAppender
log4j.appender.file.maxFileSize=5000KB
log4j.appender.file.maxBackupIndex=10
log4j.appender.file.File=${catalina.home}/logs/web.log
log4j.appender.file.layout=org.apache.log4j.PatternLayout
log4j.appender.file.layout.ConversionPattern=%d{dd-MMM HH:mm:ss} %5p %c{1}:%L - %m%n
log4j.appender.file.threshold=info

log4j.rootLogger=debug, stdout, file

Answer 1

There are two overloaded methods for error method.

1. logger.error(ex);
2. logger.error("some oops string ", ex);

if you use 1st method , which will only print the name of the Exception. if you use 2nd method, some message along with exception which will print complete stack trace similar to e.printStackTrace() method.

Answer 2

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/