Log4j 简单概念及示例.

Loggers, Appenders and Layouts

Log4j has three main components: loggers, appenders and layouts. These three 



types of components work together to enable developers to log messages according 



to message type and level, and to control at runtime how these messages are 



formatted and where they are reported.



This rule is at the heart of log4j. It assumes that levels are ordered. For the 



standard levels, we have DEBUG < INFO < WARN < ERROR < FATAL.



Appender:

 an output destination is called an appender.

For example, if a console appender is added to the root logger, then all enabled 



logging requests will at least print on the console.







Here is a sample configuration file that results in identical output as the previous BasicConfigurator based example.



------------------------------------------------

# Set root logger level to DEBUG and its only appender to A1.

log4j.rootLogger=DEBUG, A1



# A1 is set to be a ConsoleAppender.

log4j.appender.A1=org.apache.log4j.ConsoleAppender



# A1 uses PatternLayout.

log4j.appender.A1.layout=org.apache.log4j.PatternLayout

log4j.appender.A1.layout.ConversionPattern=%-4r [%t] %-5p %c %x - %m%n

 





Suppose we are no longer interested in seeing the output of any component belonging to the com.foo package. The following configuration file shows one possible way of achieving this.





log4j.rootLogger=DEBUG, A1

log4j.appender.A1=org.apache.log4j.ConsoleAppender

log4j.appender.A1.layout=org.apache.log4j.PatternLayout



# Print the date in ISO 8601 format

log4j.appender.A1.layout.ConversionPattern=%d [%t] %-5p %c - %m%n



# Print only messages of level WARN or above in the package com.foo.

log4j.logger.com.foo=WARN 



-----------------------------



log4j.rootLogger=debug, stdout, R



log4j.appender.stdout=org.apache.log4j.ConsoleAppender

log4j.appender.stdout.layout=org.apache.log4j.PatternLayout



# Pattern to output the caller's file name and line number.

log4j.appender.stdout.layout.ConversionPattern=%5p [%t] (%F:%L) - %m%n



log4j.appender.R=org.apache.log4j.RollingFileAppender

log4j.appender.R.File=example.log



log4j.appender.R.MaxFileSize=100KB

# Keep one backup file

log4j.appender.R.MaxBackupIndex=1



log4j.appender.R.layout=org.apache.log4j.PatternLayout

log4j.appender.R.layout.ConversionPattern=%p %t %c - %m%n

 





Calling the enhanced MyApp with the this configuration file will output the following on the console.



 INFO [main] (MyApp2.java:12) - Entering application.

DEBUG [main] (Bar.java:8) - Doing it again!

 INFO [main] (MyApp2.java:15) - Exiting application.



-----------------------------------------------




 
   



  
    
#ERROR为等级,FILE为Appender

log4j.rootLogger=ERROR,CONSOLE,FILE

#定义一个新的logger,名称为admin,可通过Logger.getLogger("admin")获得,继承了rootLogger的配置

log4j.logger.admin=WARN



log4j.appender.CONSOLE=org.apache.log4j.ConsoleAppender

log4j.appender.CONSOLE.layout=org.apache.log4j.PatternLayout

log4j.appender.CONSOLE.layout.conversionPattern=%p-[%d] -%M (%F\:%L) %m%n%n



log4j.appender.FILE=org.apache.log4j.RollingFileAppender

log4j.appender.FILE.File=c\:/risen_app.log

log4j.appender.FILE.MaxFileSize=2000KB

log4j.appender.FILE.MaxBackupIndex=1

log4j.appender.FILE.layout=org.apache.log4j.PatternLayout

log4j.appender.FILE.layout.ConversionPattern=%d %-5p %c - %m%n




 
   

//MyApp.java



package com.test.log4j;



import org.apache.log4j.BasicConfigurator;

import org.apache.log4j.Logger;



public class MyApp {

	// Define a static logger variable so that it references the

	// Logger instance named "MyApp".

	static Logger log=Logger.getLogger(MyApp.class);

	//按名称取logger

	//static Logger log=Logger.getLogger("admin");

	public static void main(String[] args) {

		 // Set up a simple configuration that logs on the console.

	     BasicConfigurator.configure();

		log.debug("MyApp 启动");

		Foo f=new Foo();

		f.doIt();

		log.fatal("MyApp 中止");

		

	}

}



//Foo.java



package com.test.log4j;

import org.apache.log4j.Logger;

public class Foo {

	static Logger log=Logger.getLogger(Foo.class);

	public void doIt(){

		

		log.info("Foo DoIt.");

	}

}

log4j.properties

log4j.rootLogger=INFO,FILE

#定义一个新的logger,名称为admin,可通过Logger.getLogger("admin")获得,继承了rootLogger的配置

log4j.logger.admin=DEBUG



log4j.appender.CONSOLE=org.apache.log4j.ConsoleAppender

log4j.appender.CONSOLE.layout=org.apache.log4j.PatternLayout

log4j.appender.CONSOLE.layout.conversionPattern=%p-[%d] -%M (%F\:%L) %m%n%n



log4j.appender.FILE=org.apache.log4j.RollingFileAppender

log4j.appender.FILE.File=c\:/wcg.log

log4j.appender.FILE.MaxFileSize=2000KB

log4j.appender.FILE.MaxBackupIndex=1

log4j.appender.FILE.layout=org.apache.log4j.PatternLayout

log4j.appender.FILE.layout.ConversionPattern=%d %-5p %c - %m%n