Maven Plugin Logger Compatibility

Question

I am writing a Maven plugin (Mojo) that imports a Jar library used by other projects. At least one of the classes in that library use Apache Log4j for logging, but Log4j is not going to be properly configured by the logger that Maven provides to the Mojo.

Is there any simple way to bridge between these? Unfortunately, org.apache.log4j.Logger and org.apache.maven.logging.Log do not share a common superinterface or superclass, so I can't simply have a setLog() type function. Any suggestions would be welcome; currently I am planning to either just ignore it, or write a bridge class that can use either.

Answer 1

I had the same problem and solved writing a simple bridge across Maven Logger and Log4j:

import org.apache.log4j.AppenderSkeleton;
import org.apache.log4j.Level;
import org.apache.log4j.spi.LoggingEvent;
import org.apache.maven.plugin.logging.Log;

public class MavenLoggerLog4jBridge extends AppenderSkeleton {
    private Log logger;

    public MavenLoggerLog4jBridge(Log logger) {
        this.logger = logger;
    }

    protected void append(LoggingEvent event) {
        int level = event.getLevel().toInt();
        String msg = event.getMessage().toString();
        if (level == Level.DEBUG_INT || level == Level.TRACE_INT) {
            this.logger.debug(msg);
        } else if (level == Level.INFO_INT) {
            this.logger.info(msg);
        } else if (level == Level.WARN_INT) {
            this.logger.warn(msg);
        } else if (level == Level.ERROR_INT || level == Level.FATAL_INT) {
            this.logger.error(msg);
        }
    }

    public void close() {
    }

    public boolean requiresLayout() {
        return false;
    }
}

And in my Mojo, I used the BasicConfigurator class of Log4j API, with an instance of this bridge:

public void execute() throws MojoExecutionException {
    org.apache.maven.plugin.logging.Log mavenLogger = getLog();
    BasicConfigurator.configure(new MavenLoggerLog4jBridge(mavenLogger));
}

I don't know if Maven infrastructure already have this bridge, I haven't tried to search something more "maven-like", but this solution worked fine.

Answer 2

If you want to write a bridge class, look at SLF4J sources: http://www.slf4j.org/legacy.html#log4j-over-slf4j They are doing something quite similar in their log4j bridge.