OSGL Logging is yet another Java Logging facade.

I don't like the Slf4J Logger's API. Specifically the logging API with Throwable arguments, e.g.

void debug(String msg, Throwable t);

The better one in my mind should be

void debug(Throwable t, String format, Object... args);

And yes OSGL logging Logger use the better one ;-)

1. Classic usage

import org.osgl.logging.*;

public class Foo {

    protected final Logger logger = LogManager.get(Foo.class);

    private void bar(int n) {
        logger.trace("enter bar with %s", n);
        try {
            // do something dangerous
        } catch (Exception e) {
            logger.error(e, "error executing bar with %s", n);
        }
    }
}

2. Use LogManager's static log methods

import org.osgl.logging.*;

public class Foo {
    private void bar(int n) {
        LogManager.trace("enter bar with %s", n);
        try {
            // do something dangerous
        } catch (Exception e) {
            LogManager.error(e, "error executing bar with %s", n);
        }
    }
}

3. Use LogManager's alias L and the static log methods

import org.osgl.logging.*;

public class Foo {
    private void bar(int n) {
        L.trace("enter bar with %s", n);
        try {
            // do something dangerous
        } catch (Exception e) {
            L.error(e, "error executing bar with %s", n);
        }
    }
}

The only configuration for OSGL logging is to configure the LogServiceProvider:

import org.osgl.logging.*;
import org.osgl.logging.service.*;

public class Bootstrap {
    static {
        LogManager.registerLogServiceProvider(new CommonsLoggingServiceProvider());
    }
}

At the moment there are four predefined LogServiceProvider:

1. CommonsLoggingServiceProvider, bridge to Apache Commons-Logger
2. Log4jServiceProvider, bridge to Apache Log4J
3. Slf4jServiceProvider, bridge to Slf4j
4. TinyLogServiceProvider, bridge to TinyLog

Please refer to relevant logging framework documents to check how to configure specific log service.

If user application does not explicitly register log service provider to LogManager, then LogManager will automatically discover the underline LogService by trying to check if a certain Java Class is in the class path. The discovery is proceeded with the following order:

1. Check if TinyLog is in the class path. If found then use TinyLogServiceProvider
2. Else then check if Slf4j is in the class path. If found then use Slf4jServiceProvider
3. Else then check if Commons-Logging is in the class path. If found then use CommonsLoggingServiceProvider
4. Else check if Log4j is in the class path. If found then use Log4jServiceProvider
5. Finally if none of the service provider is used, then by default use JDKLogService