Please make sure you read and understand this before moving forward: TOPICS: Logging
Ok, so now you know about what logging is and why we do it, we’re going to dig a bit more into some specific details about how to do this stuff in Java.
We are using IntelliJ and Gradle. This means we have a specific way of including Log4j in our projects.
The first thing you need to do is make sure you have added Log4j as a dependency on your project. Take a look here and here to see how to add Log4j to your project.
Now make a new project and log some stuff:
import org.apache.logging.log4j.LogManager;
import org.apache.logging.log4j.Logger;
public class MainProgram {
private static final Logger logger = LogManager.getLogger(MainProgram.class.getName());
public static void main(String[] args){
logger.debug("Hello this is a debug message");
logger.info("Hello this is an info message");
logger.warn("Hello this is a warning message");
logger.error("Hello this is an error message");
logger.fatal("Hello this is a fatal message"); // some languages call this level "critical"
}
}
If you run this then you’ll see some of the messages get logged to the standard output. But you’ll also see an error message.
IntlliJ will show you an error message that says “ERROR StatusLogger No Log4j 2 configuration file found. Using default configuration (logging only errors to the console), …”
Now make a new file in the resources firectory and name it log4j2-test.properties. Here’s what it should look like:
appender.console.name = STDOUT
appender.console.type = Console
appender.console.layout.type = PatternLayout
appender.console.layout.pattern = %d | %c: %m%n
rootLogger.level = debug
rootLogger.appenderRef.stdout.ref = STDOUT
Save it and run your program again. Now all the logs should show up with some fancy formatting.
We just scratched the surface here. Try use logging for now on instead of just System.out.println. In industry you’ll have to get used to logging things in a thoughtful way.