Logging with Log4J - LAMS 2

Logging

All logging is done using Log4j (http://logging.apache.org/log4j/).

At the top of your class, define a static logger:

private static Logger log = Logger.getLogger(<classname>.class);

Then when putting in a log statement, you just do:

log.debug("This is the log message");

Please think about the log levels and use appropriately. Your code should have more than just log.debug statements! There is also info, warn, error, etc!

Also remember to use isDebugEnabled() appropriately. If your debug statement would take some effort to generate then stop the call occuring using isDebugEnabled(). But if the log message is very simple (say a concatenation of two strings), then it isn't worthwhile using isDebugEnabled(). This will help performance.

For example, assume you have an object blah that has a toString method that prints the values of 15 fields and contains some other complex objects, when method validateBlah(Blah blah) is called. If the log statement wanta to dump out the object then do:

private boolean validateBlah(Blah blah) {

    if ( log.isDebugEnabled() ) {
        log.debug("--> validateBlah start. Blah is "+blah);
    }

    .....

}

If all you are just logging the entry into the method don't bother with the log.isDebugEnabled() statement:

private boolean validateBlah(Blah blah) {

    log.debug("--> validateBlah start.");
    .....

}