Debug flag for jsp web application

Question

I have a jsp web application where I print the error stacktrace as follows:

    catch (SQLException e) {
        e.printStackTrace(System.out);
    }

but in production environment I do not want my application to print something. I want to put a global flag (Debug = true for example) . then I will update the codes like this

  if(debug) e.printStackTrace(System.out);

I have many pages in my application. Now where should i declare the debug variable ? I can put it in web.xml file but I am not sure if its safe or not.Thanks

Answer 1

Use a logging API like JB Nizet suggests. They are rather simple to use. Here's a small example to implement logging using Log4j from Apache ( http://logging.apache.org/log4j ) which is very popular.

All your classes would have an instance of logger ready

private static final Logger log = Logger.getLogger(this.getClass());

Then at places where you catch exceptions

catch (SQLException e) {
    log.debug(e);
}

Then just configure Log4j using log4j.properties in your classpath

log4j.appender.stdout.Target=System.out
log4j.appender.stdout=org.apache.log4j.ConsoleAppender
log4j.appender.stdout.layout=org.apache.log4j.SimpleLayout

log4j.rootLogger=debug, stdout

To turn of logging is then as simple as changing

log4j.rootLogger=warn, stdout

What this means is that you're only interested in log statements that are at a level of warning or above (like error, or fatal). There are about six log levels: fatal, error, warn, info, debug and trace. When you set a level all log statements that log at a level below what you've specified are ignored.

Please, note that I've simplified things above. It's recommended to use log4j.xml instead of .properties . Latest APIs also allow you to gain some performance with a check done before logging

catch (SQLException e) {
    if (log.isDebugEnabled()) log.debug(e);
}

But, the real selling point of using the framework instead of just checking a Globals.DEBUG flag before doing a printStackTrace() is that it's future proof. Say tomorrow if you have to log things to a file just switch from ConsoleAppender to a FileAppender . Want an email delivered on something fatal use an SMTPAppender for just this use case. Other appenders stay configured as they are.