slf4j 与 log4j2 基本用法
简单的说 log4j2 是log4j的升级版，解决了部分性能和死锁问题，其使用方式与使用配置与log4j相同。
建议使用maven依赖直接使用log4j2
<dependency> <groupId>org.apache.logging.log4jgroupId> <artifactId>log4j-apiartifactId> <version>2.17.1version> dependency> <dependency> <groupId>org.apache.logging.log4jgroupId> <artifactId>log4j-coreartifactId> <version>2.17.1version> dependency>
获取logger实例的方法为
Logger logger = LogManager.getLogger(Test.class);
logger的基本配置如下（参考SeanXiao）
<?xml version="1.0" encoding="UTF-8"?> <configuration status="error"> <Properties> <Property name="fileName">front.logProperty> <Property name="backupFilePatch">d:/usr/front/log/Property> Properties> <appenders> <Console name="Console" target="SYSTEM_OUT"> <ThresholdFilter level="trace" onMatch="ACCEPT" onMismatch="DENY" /> <PatternLayout pattern="%d{HH:mm:ss.SSS} %-5level %class{36} %L %M - %msg%xEx%n" /> Console> <RollingFile name="RollingFile" fileName="${backupFilePatch}/${fileName}" filePattern="${backupFilePatch}$${date:yyyy-MM}/app-%d{yyyyMMddHHmmssSSS}.log.gz"> <PatternLayout pattern="%d{yyyy.MM.dd 'at' HH:mm:ss.SSS z} %-5level %class{36} %L %M - %msg%xEx%n" /> <SizeBasedTriggeringPolicy size="20MB" /> <DefaultRolloverStrategy max="20"/> RollingFile> appenders> <loggers> <Logger name="com.testlog" level="trace" additivity="true"> <AppenderRef ref="RollingFile" /> Logger>
<Root level="error">
<AppenderRef ref="Console" />
Root>
loggers>
configuration>
appenders 用于定义日志的格式，包含了Console 和 RollingFile 两种格式，分别
Console的level是trace，而RollingFile没有定义自己的日志级别level，由引用的loggers定义
loggers 真正的将appdender应用生效，log4j2根据Logger和Root的定义写入相应的appender格式的日志
例子
package com.testlog; import org.apache.logging.log4j.LogManager; import org.apache.logging.log4j.Logger; public class Test { public static void main(String [] args) { Logger logger = LogManager.getLogger(Test.class); logger.error("error accu"); logger.info("test"); } }
控制台日志
23:50:47.551 ERROR testlog.Test 11 main - error accu
23:50:47.551 INFO testlog.Test 12 main - test
日志文件
2017.05.16 at 23:50:47.551 CST ERROR testlog.Test 11 main - error accu
2017.05.16 at 23:50:47.551 CST INFO testlog.Test 12 main - test
日志级别：
trace： 是追踪，就是程序推进以下，你就可以写个trace输出，所以trace应该会特别多，不过没关系，我们可以设置最低日志级别不让他输出。
debug： 调试么，我一般就只用这个作为最低级别，trace压根不用。是在没办法就用eclipse或者idea的debug功能就好了么。
info： 输出一下你感兴趣的或者重要的信息，这个用的最多了。
warn： 有些信息不是错误信息，但是也要给程序员的一些提示，类似于eclipse中代码的验证不是有error 和warn（不算错误但是也请注意，比如以下depressed的方法）。
error： 错误信息。用的也比较多。
fatal： 级别比较高了。重大错误，这种级别你可以直接停止程序了，是不应该出现的错误么！不用那么紧张，其实就是一个程度的问题。
部分系统使用了slf4j，此时可以将引用库统一使用log4j2作为底层实现，保证日志的统一
slf4j maven
<dependency> <groupId>org.apache.logging.log4jgroupId> <artifactId>log4j-slf4j-implartifactId> <version>2.17.1version> dependency>
引用方式
package com.testlog; import org.slf4j.Logger; import org.slf4j.LoggerFactory; public class Test { public static void main(String [] args) { Logger logger = LoggerFactory.getLogger(Test.class); logger.error("error accu"); logger.info("test"); } }
打出的日志与log4j2的日志相同
apache log4j2配置文件配置说明
http://logging.apache.org/log4j/2.x/manual/configuration.html
举个例子Spring中引用slf4j替换其原本的common-logging的方式
<dependency>
<groupId>org.springframeworkgroupId>
<artifactId>spring-coreartifactId>
<version>4.3.2.RELEASEversion>
<exclusions>
<exclusion>
<groupId>commons-logginggroupId>
<artifactId>commons-loggingartifactId>
exclusion>
exclusions>
dependency>
<dependency>
<groupId>org.springframeworkgroupId>
<artifactId>spring-beansartifactId>
<version>4.3.2.RELEASEversion>
dependency>
<dependency>
<groupId>org.springframeworkgroupId>
<artifactId>spring-contextartifactId>
<version>4.3.2.RELEASEversion>
dependency>
<dependency>
<groupId>org.slf4jgroupId>
<artifactId>jcl-over-slf4jartifactId>
<version>1.7.25version>
dependency>
Spring标准配置
<?xml version="1.0" encoding="UTF-8"?> <beans xmlns="http://www.springframework.org/schema/beans" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:util="http://www.springframework.org/schema/util" xmlns:context="http://www.springframework.org/schema/context" xsi:schemaLocation="http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans-4.1.xsd http://www.springframework.org/schema/context http://www.springframework.org/schema/context/spring-context-4.1.xsd"> <context:component-scan base-package="com.ingchat" /> beans>
将log4j2.xml中的Root更改为trace，用于查看Spring中的日志
<loggers>
<Logger name="com.ingchat.testlog" level="trace"
additivity="true">
<AppenderRef ref="RollingFile" />
Logger>
<Root level="trace">
<AppenderRef ref="Console" />
Root>
loggers>
Java代码如下所示
package com.ingchat.testlog;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
import org.springframework.context.ApplicationContext;
import org.springframework.context.support.ClassPathXmlApplicationContext;
import org.springframework.stereotype.Component;
/**
* Hello world!
*
*/
@Component
public class App {
private Logger logger = LoggerFactory.getLogger(App.class);
public void show() {
logger.error("error accu 333");
logger.info("test 444");
}
public static void main(String[] args) {
ApplicationContext ctx = new ClassPathXmlApplicationContext("classpath:applicationContext.xml");
App app = ctx.getBean(App.class);
app.show();
System.out.println("Hello World!");
}
}
打出的日志如下15:29:12.028 DEBUG org.springframework.core.env.MutablePropertySources 109 addLast - Adding [systemProperties] PropertySource with lowest search precedence
15:29:12.033 DEBUG org.springframework.core.env.MutablePropertySources 109 addLast - Adding [systemEnvironment] PropertySource with lowest search precedence 15:29:12.033 DEBUG org.springframework.core.env.AbstractEnvironment 127- Initialized StandardEnvironment with PropertySources [systemProperties,systemEnvironment] ......
15:29:12.376 TRACE org.springframework.core.io.support.SpringFactoriesLoader 89 loadFactories - Loaded [org.springframework.beans.BeanInfoFactory] names: [org.springframework.beans.ExtendedBeanInfoFactory] 15:29:12.377 TRACE org.springframework.beans.CachedIntrospectionResults 265- Getting BeanInfo for class [com.ingchat.testlog.App] 15:29:12.381 TRACE org.springframework.beans.CachedIntrospectionResults 284 - Caching PropertyDescriptors for class [com.ingchat.testlog.App] 15:29:12.381 TRACE org.springframework.beans.CachedIntrospectionResults 297 - Found bean property 'class' of type [java.lang.Class] ...... 15:29:12.424 TRACE org.springframework.context.support.AbstractApplicationContext 362 publishEvent - Publishing event in org.springframework.context.support.ClassPathXmlApplicationContext@3d7bcb17: org.springframework.context.event.ContextRefreshedEvent[source=org.springframework.context.support.ClassPathXmlApplicationContext@3d7bcb17: startup date [Wed May 17 15:29:12 CST 2017]; root of context hierarchy] 15:29:12.427 TRACE org.springframework.core.env.PropertySourcesPropertyResolver 78 getProperty - Searching for key 'spring.liveBeansView.mbeanDomain' in [systemProperties] 15:29:12.427 TRACE org.springframework.core.env.PropertySourcesPropertyResolver 78 getProperty - Searching for key 'spring.liveBeansView.mbeanDomain' in [systemEnvironment] 15:29:12.427 DEBUG org.springframework.core.env.PropertySourcesPropertyResolver 91 getProperty - Could not find key 'spring.liveBeansView.mbeanDomain' in any property source 15:29:12.429 DEBUG org.springframework.beans.factory.support.AbstractBeanFactory 251 doGetBean - Returning cached instance of singleton bean 'app' 15:29:12.430 ERROR com.ingchat.testlog.App 17 show - error accu 333 15:29:12.430 INFO com.ingchat.testlog.App 18 show - test 444 Hello World!
可参考http://www.cnblogs.com/yinz/p/5695995.html
本文参考：
http://blog.csdn.net/clementad/article/details/44625787
http://blog.csdn.net/lu8000/article/details/25754415
log4j2配置详细说明
https://www.cnblogs.com/kevin-yuan/archive/2012/11/23/2784610.html