log4j 介绍（7）-- Example篇

在实际项目中，一般会采用读取配置文件的方式进行log控制，最常用的是log4j.properties

第一步： 新建一个java工程，名字就叫： logExample1
第二步： 在src目录下新建log4j.properties文件
代码如下：

#define the root logger
#appender's name is file and the level is INFO
log4j.rootLogger = INFO, file


log4j.appender.file = org.apache.log4j.RollingFileAppender

#the output file's name and directory
log4j.appender.file.File = ./out.log
log4j.appender.file.layout = org.apache.log4j.PatternLayout
log4j.appender.file.layout.ConversionPattern=%5p [%t] (%F:%L) - %m%n

第三步：创建MyApp类，代码如下

package com.noodle.util;
import org.apache.log4j.Logger;
import com.noodle.pojo.Movie;

public class MyApp {
	static Logger logger = Logger.getLogger(MyApp.class);
		
	public static void main(String[] args){
		logger.info("application begin in main");
		Movie movie = new Movie();
		movie.watchIt();
		logger.info("application end in main");
	}
}

第四步：创建Movie类， 代码如下

package com.noodle.pojo;

public class Movie {
	static org.apache.log4j.Logger logger  = org.apache.log4j.Logger.getLogger(Movie.class);
	
	public void watchIt(){
		logger.warn("Watch movie");		
	}
}

第五步： 结果在logExample1目录下生成out.log里面的内容是：
INFO [main] (MyApp.java:12) - application begin in main
WARN [main] (Movie.java:7) - Watch movie
INFO [main] (MyApp.java:17) - application end in main

如果要跟踪一个事件，单独为这个事件，设定日志。 那么需要一个Logger instance 穿插于各个class之间，这样在properites里如何去写呢？

log4j.properties:

#define the root logger
#appender's name is file and the level is INFO
log4j.rootLogger = INFO, file


log4j.appender.file = org.apache.log4j.RollingFileAppender

#the output file's name and directory
log4j.appender.file.File = ./out.log
log4j.appender.file.layout = org.apache.log4j.PatternLayout
log4j.appender.file.layout.ConversionPattern=%5p [%t] (%F:%L) - %m%n


log4j.logger.eventLogName = INFO, eventlog

#Properties are case sensitive.
#log4j.logger.EVENTLOGNAME = INFO, eventlog
#that is unable to print the log messages in the console.

log4j.appender.eventlog = org.apache.log4j.ConsoleAppender
log4j.appender.eventlog.layout = org.apache.log4j.PatternLayout
log4j.appender.eventlog.layout.ConversionPattern = %d{dd-MM-yyyy}, %d{HH:mm:ss}, %-5.5p, %m %n 

MyApp.java

package com.noodle.util;
import org.apache.log4j.Logger;

import com.noodle.help.AppConstant;
import com.noodle.pojo.Movie;

public class MyApp {
	static Logger logger = Logger.getLogger(MyApp.class);
	static Logger eventlogger = Logger.getLogger(AppConstant.EVENT);
	
	public static void main(String[] args){
		logger.info("application begin in main");
		eventlogger.info("this is the begin of the eventlog");
		Movie movie = new Movie();
		movie.watchIt();
		eventlogger.info("this is the end of the eventlog");		
		logger.info("application end in main");
	}
}

Movie.java

package com.noodle.pojo;

public class Movie {
	static org.apache.log4j.Logger logger  = org.apache.log4j.Logger.getLogger(Movie.class);
	
	public void watchIt(){
		logger.warn("Watch movie");		
	}
}

定义一个AppConstant.java

package com.noodle.help;

public class AppConstant {
	public final static String EVENT = "eventLogName";
}

这样，去运行以下，得到的结果是：
在out.log日志里输出：

INFO [main] (MyApp.java:12) - application begin in main
INFO [main] (MyApp.java:13) - this is the begin of the eventlog
WARN [main] (Movie.java:7) - Watch movie
INFO [main] (MyApp.java:16) - this is the end of the eventlog
INFO [main] (MyApp.java:17) - application end in main

而同时在控制台里输出了：
18-08-2009, 20:37:20, INFO , this is the begin of the eventlog
18-08-2009, 20:37:20, INFO , this is the end of the eventlog

Enjoy it!