log4j not printing the stacktrace for exceptions

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

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/

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.

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.

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);
}

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

I haven't used the fillStackTrace call, so I cannot comment if that will work. Another approach is to use a little method that returns the formatted text from an Exception.

public static String getStackTrace(Exception e)
{
	StringWriter sWriter = new StringWriter();
	PrintWriter pWriter = new PrintWriter(sWriter);
	e.printStackTrace(pWriter);
	return sWriter.toString();
}

In your logging code, you could write:

logger.error("An exception occurred: " + Utils.getStackTrace(e));

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);
}
        

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 {