On Wednesday 12 October 2005 08:24, Trustin Lee wrote:
> This monitor pattern is overengineering IMHO.  Why should I add extra
> methods whenever I write debug log messages and provide a bridge for known
> logging frameworks?  And we can say using monitors is implementing AOP
> almost by hand.

If you take it at face value, and don't adopt it to your need, then I agree 
that it is over-engineered and an explosion of classes will result.

However, there is a principle in there, which I find good. That you should 
isolate your dependencies to a single point if possible. And in case of 
logging, that is so simple to do.


public interface OurLogger
{
    // Add methods you need.
    boolean isDebugEnabled();
    void debug( String message );
    void info( String message );
    void warn( String message, Throwable t );
    void error( String message, Throwable t );
}

public class OurLoggerBridgeToLog4J
{
    private Logger m_logger;

    public OurLoggerBridgeToLog4J( Class cls )
    {
        m_logger = Logger.getLogger( cls );
    }

    public boolean isDebugEnabled()
    {
        return m_logger.isDebugEnabled();
    }

    public void debug( String message )
    {
        m_logger.debug( message );
    }

    public void info( String message )
    {
        m_logger.info( message );
    }

    public void warn( String message, Throwable t )
    {
        m_logger.warn( message, t );
    }

    public void error( String message, Throwable t )
    {
        m_logger.error( message, t );
    }
}

public class OurLoggerFactory
{
    public OurLogger getLogger( Class cls )
    {
        // introduce some selector if needed.
        return new OurLoggerBridgeToLog4J( cls );
    }
}

Ok, that took ~10 minutes.
To be more embeddor friendly, introduce a delegation mechanism in the 
OurLoggerFactory. Ok, that will take another 10mins.


Considering the reduction of depending on external stuff to a single point 
(one class + a factory), the amount of effort required is neglectable.

THAT is what I kept from Hammant's insight. And I am a bit surprised that more 
people doesn't see the beauty of this ;o)


Cheers
Niclas