log4j入门级介绍

=Simple Log4j Configuration= Log4j is a simple and flexible logging framework. In this tutorial you will learn how to configure log4j for your applications. Let's get started first download the latest version of log4j. I am using log4j version 1.2.15. Add the //log4j-1.2.15.jar// to the classpath. Next you need to create an instance of Logger class. You can create one using the //Logger.getLogger(HelloWorld.class)// method. It takes one argument the fully qualified class name. Now we need to configure log4j. The simple way to do that is using //BasicConfigurator. configure// method. This will log all the messages on the console. Now everything is ready you can log messages using any of the print statements of the //Logger// class. In the following code I use the //debug// method to display the "//HelloWorld!//" message. code format="java" import org.apache.log4j.BasicConfigurator; import org.apache.log4j.Logger; public class HelloWorld { static final Logger logger = Logger.getLogger(HelloWorld.class); public static void main(String[] args) { BasicConfigurator.configure; logger.debug("Hello World!"); } } code The other methods available are //info, warn, error and fatal//. Each method represents a logger level namely //DEBUG, INFO, WARN, ERROR// and //FATAL.// The following example shows how to use these methods. code format="java" import org.apache.log4j.BasicConfigurator; import org.apache.log4j.Logger;

public class HelloWorld { static final Logger logger = Logger.getLogger(HelloWorld.class);

public static void main(String[] args) { BasicConfigurator.configure; logger.debug("Sample debug message"); logger.info("Sample info message"); logger.warn("Sample warn message"); logger.error("Sample error message"); logger.fatal("Sample fatal message"); } } code Here is the output of the above code. 1. 0 [main] DEBUG com.vaannila.helloworld.HelloWorld - Sample debug message 2. 0 [main] INFO com.vaannila.helloworld.HelloWorld - Sample info message 3. 0 [main] WARN com.vaannila.helloworld.HelloWorld - Sample warn message 4. 0 [main] ERROR com.vaannila.helloworld.HelloWorld - Sample error message 5. 0 [main] FATAL com.vaannila.helloworld.HelloWorld - Sample fatal message The output contains the time elapsed from the start of the program in milliseconds, the thread name, the logger level, the class name and the log message.