日志系统组件框架之版本兼容性

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【导读】日志系统六大组件：slf4j-log4j、slf4j-simple、slf4j-jdk14、slf4j-nop、slf4j-jcl、logback-classic;

2014-05-21_004834

最近项目从 Maven 迁移至 Gradle ，在build.gradle 依赖配置中遇到日志系统版本兼容性问题（备注：Maven 中一切正常;( … ）；在解决过程中，随便梳理下日志系统下所有日志组件框架：slf4j-log4j、slf4j-simple、slf4j-jdk14、slf4j-nop、slf4j-jcl、logback-classic;

本文章从以下两方面进行描述：

日志系统六大组件介绍
六大组件各自体系与SLF4J-API版本兼容性

日志系统六大组件介绍

slf4j-log4j：

Binding for log4j version 1.2, a widely used logging framework. You also need to place log4j.jar on your class path

slf4j-simple：

Binding for Simple implementation, which outputs all events to System.err. Only messages of level INFO and higher are printed. This binding may be useful in the context of small applications.

slf4j-jdk14：

Binding for java.util.logging, also referred to as JDK 1.4 logging

slf4j-nop：

Binding for NOP, silently discarding all logging.

slf4j-jcl：

Binding for Jakarta Commons Logging. This binding will delegate all SLF4J logging to JCL.

logback-classic：

NATIVE IMPLEMENTATION There are also SLF4J bindings external to the SLF4J project, e.g. logback which implements SLF4J natively. Logback’s ch.qos.logback.classic.Logger class is a direct implementation of SLF4J’s org.slf4j.Logger interface. Thus, using SLF4J in conjunction with logback involves strictly zero memory and computational overhead.

以上内容请到官网查看：http://www.slf4j.org/manual.html

六大组件各自体系与SLF4J-API版本兼容性

2014-05-21_012407

由上图可以得出：

1） slf4j-api由两个时期版本组成

slf4j-api分为 1.5.5 和 1.5.5之前版本及 1.5.6和1.5.6之后版本，主要不同之处：

StaticLoggerBinder.java

1.5.5 And below 1.5.5

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privatestaticorg.slf4j.impl.StaticLoggerBinder SINGLETON;

1.5.6 And above 1.5.6

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/*** The unique instance of this class.**/privatestaticfinal StaticLoggerBinder SINGLETON = newStaticLoggerBinder(); /*** Return the singleton of this class.** @return the StaticLoggerBinder singleton*/publicstaticfinal StaticLoggerBinder getSingleton() {returnSINGLETON;}

如果日志组件框架版本与slf4j-api 不一致，很可能会抛异常：

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Exception in thread"main"java.lang.IllegalAccessError: tried to access field org.slf4j.impl.StaticLoggerBinder.SINGLETON fromclassorg.slf4j.LoggerFactory at org.slf4j.LoggerFactory.<clinit>(LoggerFactory.java:60)

2）slf4j-log4j、slf4j-simple、slf4j-jdk14、slf4j-nop、slf4j-jcl、logback-classic 与 slf4j-api 版本相匹配

slf4j-log4j、slf4j-simple、slf4j-jdk14、slf4j-nop、slf4j-jcl 这五大组件直接与slf4j-api 版本相同，这个比较容易区分；

而 logback-classic 0.9.11之前版本与 slf4j-api 1.5.5 之前版本相对应，0.9.12之后版本与 slf4j-api 1.5.6之后版本相对应，这点经过本人测试得出；

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