java开发过程中为了找问题方便或是统计信息方便,总免不了要打各种日志。之前的各个项目都是配置好的,maven配置的时候,会看到各种类型的Log包:slf4j、log4j、commons-log、logback等等,看着就烦,今天仔细了解了一下,有点收获,记录一下
起因
使用JAVA的kafka api写main方法进行开发测试,发现总报错
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log4j:WARN No appenders could be found for logger (kafka.utils.VerifiableProperties).
log4j:WARN Please initialize the log4j system properly.
log4j:WARN See http: //logging .apache.org /log4j/1 .2 /faq .html #noconfig for more info.
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解决过程
第一直觉是缺少log4j的配置。好办,classpath下加入log4j.properties(log4j默认应该是直接找classpath下的这个文件,当然,可以直接指定加载哪个文件),OK,不报错了
刚好最近的一个项目使用的是logback,而且网上也查了,logback性能要优于log4j(没有做过测试,先盲目从众吧),就想直接引入logback。
POM中加入logback的依赖
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<dependency>
<groupId>ch.qos.logback< /groupId >
<artifactId>logback-core< /artifactId >
<version>1.1.2< /version >
< /dependency >
<dependency>
<groupId>ch.qos.logback< /groupId >
<artifactId>logback-access< /artifactId >
<version>1.1.2< /version >
< /dependency >
<dependency>
<groupId>ch.qos.logback< /groupId >
<artifactId>logback-classic< /artifactId >
<version>1.1.2< /version >
< /dependency >
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启动,报错
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log4j:WARN No appenders could be found for logger (kafka.utils.VerifiableProperties).
log4j:WARN Please initialize the log4j system properly.
log4j:WARN See http: //logging .apache.org /log4j/1 .2 /faq .html #noconfig for more info.
SLF4J: Class path contains multiple SLF4J bindings.
SLF4J: Found binding in [jar: file : /C : /Users/zhaohuayu/ .m2 /repository/org/slf4j/slf4j-log4j12/1 .6.1 /slf4j-log4j12-1 .6.1.jar! /org/slf4j/impl/StaticLoggerBinder .class]
SLF4J: Found binding in [jar: file : /C : /Users/zhaohuayu/ .m2 /repository/ch/qos/logback/logback-classic/1 .1.2 /logback-classic-1 .1.2.jar! /org/slf4j/impl/StaticLoggerBinder .class]
SLF4J: See http: //www .slf4j.org /codes .html #multiple_bindings for an explanation.
SLF4J: Actual binding is of type [org.slf4j.impl.Log4jLoggerFactory]
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哦,Class path contains multiple SLF4J bindings。
原来slf4j提供的是一个抽象的接口,实现可以是log4j、logback等,但是,运行时候只能有一个接口实现类。之前引入的kafka包,已经包含了对log4j的依赖,我又引入logback的包,冲突了
好办,去掉对Log4j的依赖
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<dependency>
<groupId>org.apache.kafka< /groupId >
<artifactId>kafka_2.10< /artifactId >
<version>0.8.2.0< /version >
<exclusions>
<exclusion>
<groupId>log4j< /groupId >
<artifactId>log4j< /artifactId >
< /exclusion >
<exclusion>
<groupId>org.slf4j< /groupId >
<artifactId>slf4j-log4j12< /artifactId >
< /exclusion >
< /exclusions >
< /dependency >
<dependency>
<groupId>ch.qos.logback< /groupId >
<artifactId>logback-core< /artifactId >
<version>1.1.2< /version >
< /dependency >
<dependency>
<groupId>ch.qos.logback< /groupId >
<artifactId>logback-access< /artifactId >
<version>1.1.2< /version >
< /dependency >
<dependency>
<groupId>ch.qos.logback< /groupId >
<artifactId>logback-classic< /artifactId >
<version>1.1.2< /version >
< /dependency >
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这下总OK了吧,运行:
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Exception in thread "main" java.lang.NoClassDefFoundError: org /apache/log4j/Logger
at kafka.utils.Logging$class.logger(Logging.scala:24)
at kafka.utils.VerifiableProperties.logger$lzycompute(VerifiableProperties.scala:26)
at kafka.utils.VerifiableProperties.logger(VerifiableProperties.scala:26)
at kafka.utils.Logging$class.info(Logging.scala:67)
at kafka.utils.VerifiableProperties.info(VerifiableProperties.scala:26)
at kafka.utils.VerifiableProperties.verify(VerifiableProperties.scala:217)
at kafka.producer.ProducerConfig.<init>(ProducerConfig.scala:57)
at KafkaProducer.getClient(KafkaProducer.java:26)
at KafkaProducer.sendMsg(KafkaProducer.java:35)
at KafkaProducer.main(KafkaProducer.java:41)
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:57)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
at java.lang.reflect.Method.invoke(Method.java:606)
at com.intellij.rt.execution.application.AppMain.main(AppMain.java:140)
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what?
kafka.utils.Logging里包含了对log4j类的引用……
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package kafka.utils;
import kafka.utils.Log4jController.;
import org.apache.log4j.Logger;
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怎么办?难道使用kafka的项目必须使用log4j?
总有解决方案,
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<dependency>
<groupId>org.slf4j< /groupId >
<artifactId>log4j-over-slf4j< /artifactId >
<version>1.7.7< /version >
< /dependency >
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再次运行,OK,日志正常打印了
总结
1、slf4j提供各种抽象接口,日志应该基于slf4j的API进行日志打印,这样无论迁移到那个项目,只需要配一个实现类log4j or logback,都能正常打印日志
2、slf4j的实现类不能有多个,不然冲突
3、如果项目中有直接引用log4j的,可以加入log4j-over-slf4j,把旧的日志log4j适配到slf4j,这时候,再使用logback就可以了。
分享一个博客中解决各个项目模块中,各种日志杂乱的方案
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<dependency>
<groupId>org.slf4j< /groupId >
<artifactId>slf4j-api< /artifactId >
<version>${org.slf4j-version}< /version >
< /dependency >
<dependency>
<groupId>org.slf4j< /groupId >
<artifactId>jcl-over-slf4j< /artifactId >
<version>${org.slf4j-version}< /version >
< /dependency >
<dependency>
<groupId>org.slf4j< /groupId >
<artifactId>log4j-over-slf4j< /artifactId >
<version>${org.slf4j-version}< /version >
< /dependency >
<dependency>
<groupId>org.slf4j< /groupId >
<artifactId>jul-to-slf4j< /artifactId >
<version>${org.slf4j-version}< /version >
< /dependency >
<dependency>
<groupId>org.jboss.logging< /groupId >
<artifactId>jboss-logging< /artifactId >
<version>3.1.4.GA< /version >
< /dependency >
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当然,前提是需要把各个项目中依赖的log实现exclusion掉