log4j是apache.logging(http://logging.apache.org/) 接口的一个java版本实现,还有log4net、log4Cxx等实现。java
整个日志器组件由三个子组件构成:数据库
一、Logger组件,负责按照级别进行输出apache
二、Appender组件:负责控制输出的目的地,如控制台,日志文件,数据库,网络等。网络
三、Layout组件:负责控制输出日志数据的格式,如:SimpleLayout。app
原理性演示代码:ide
Logger rootLogger=Logger.getRootLogger();//获取根日志器 rootLogger.setLevel(Level.INFO);//设定日志级别 /* * trace * debug * info * warn * error * fatal */ Logger logger=Logger.getLogger("com.yu");//标识为com.yu 的日志器(继承根日志器) Logger logger1=Logger.getLogger("com.yu"); System.out.println(logger==logger1);//标识符相同,日志器相同 Logger itemLogger=Logger.getLogger("com.yu.item");//标识为com.yu.item 的日志器,注意名称规则(继承) Appender a=new ConsoleAppender();//一个日志目标(控制台方向) Layout lay=new SimpleLayout();//一个格式化器 a.setLayout(lay); logger.addAppender(a); //不能输出,由于根日志器的级别debug<info logger.debug("degug"); //输出,由于根日志器的级别warn>info logger.warn("warn"); //输出,由于根日志器的级别warn>info itemLogger.warn("item warn...");
开发中,咱们须要以配置的方式使用log4j,为此能够在项目的classpath中加入文件(log4j.properties)spa
# 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
能够观察到:Logger为root,Appender为PatternLayout,Layout为PatternLayout。debug
代码以下:日志
//PropertyConfigurator.configure("log4j.properties");该行能够省略,默认读取classpath:log4j.properties Logger logger=Logger.getLogger("com.yu");//获取的任何日志器都是根日志器的子类对象 logger.warn("hello");//是否能够输出,取决于"log4j.rootLogger=error, A1"
更多的日志文件演示orm
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 输出形式以下: 2000-09-07 14:07:41,508 [main] INFO MyApp - Entering application. 2000-09-07 14:07:41,529 [main] INFO MyApp - Exiting application.
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