Java logging framework which does not require LOGGER declaration on every class

Question

I tried the following loggers

• Java Logging API
• Log4j
• slf4j

All of these requires a LOGGER declaration at the class level, like the ones below

private final static java.util.logging.Logger.Logger LOGGER = java.util.logging.Logger.Logger.getLogger(MyClass.class.getName());
private final Logger slf4jLogger = LoggerFactory.getLogger(SLF4JHello.class);
private final static Logger log4jLogger = Logger.getLogger(Log4jHello.class);

This looks hideous to me, is there an logger framework in java that does not require this declaration?

What I'm looking for is, I can have a global declaration like

private final static Logger Logger = Logger.getLogger(MyApp.class);

But when I call Logger.log(..) from class XXX.class then the Logger should make use of the XXX.class name.

Answer 1

Your problem is more than likely not with the logging framework but with the layout.

Concrete example

so35592962/App.java

package so35592962;
import org.apache.logging.log4j.*;
import so35592962.sub.OtherClass;
public class App {
  public static final Logger logger = LogManager.getLogger();
  public static void main(String[] args) {
    logger.error("in App.main");
    OtherClass.act();
  }
}

so35592962/sub/OtherClass.java

package so35592962.sub;
import static so35592962.App.logger;

public class OtherClass {
  public static void act() {
    logger.error("OtherClass.act");
  }
}

So you can see this is totally what you want: classes that use a single logger. So good point, Log4J2 can be used for that.

Now I add the magic file log4j2.xml

<?xml version="1.0" encoding="UTF-8"?>
<Configuration status="WARN">
  <Appenders>
    <Console name="Console" target="SYSTEM_OUT">
      <PatternLayout pattern="%d{HH:mm:ss.SSS} [%t] %-5level %C{36} - %msg%n"/>
    </Console>
  </Appenders>
  <Loggers>
    <Root level="error">
      <AppenderRef ref="Console"/>
    </Root>
  </Loggers>
</Configuration>

Running this will print:

12:05:28.834 [main] ERROR so35592962.App - in App.main
12:05:28.836 [main] ERROR so35592962.sub.OtherClass - OtherClass.act

Look, there are different class names here! Yet I used Log4J2.

What happened here?

Note the pattern used in the PatternLayout tag:

%d{HH:mm:ss.SSS} [%t] %-5level %C{36} - %msg%n

The standard examples and what you usually see on the Internet all use the %L pattern. This pattern is to show the logger name. But you said you don't want it. Fortunately, other patterns exist. %C will show the class name instead of the logger name. This is the pattern that is used here.

According to the PatternLayout documentation, the %C pattern does the following:

Outputs the fully qualified class name of the caller issuing the logging request.

Important note, also mentioned in the documentation:

Generating the class name of the caller (location information) is an expensive operation and may impact performance. Use with caution.