此错误出现过了几次了，有必要记录一下。
1 问题描述
运行测试用例的spring-boot Java程序片段时，报如下错误：
SLF4J: Class path contains multiple SLF4J bindings.
SLF4J: Found binding in [jar:file:/D:/Program_Data/maven_repository/org/apache/logging/log4j/log4j-slf4j-impl/2.13.3/log4j-slf4j-impl-2.13.3.jar!/org/slf4j/impl/StaticLoggerBinder.class]
SLF4J: Found binding in [jar:file:/D:/Program_Data/maven_repository/ch/qos/logback/logback-classic/1.2.3/logback-classic-1.2.3.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.apache.logging.slf4j.Log4jLoggerFactory]
java.lang.ExceptionInInitializerError
at sun.reflect.NativeConstructorAccessorImpl.newInstance0(Native Method)
at sun.reflect.NativeConstructorAccessorImpl.newInstance(NativeConstructorAccessorImpl.java:62)
at sun.reflect.DelegatingConstructorAccessorImpl.newInstance(DelegatingConstructorAccessorImpl.java:45)
at java.lang.reflect.Constructor.newInstance(Constructor.java:423)
at org.junit.runners.BlockJUnit4ClassRunner.createTest(BlockJUnit4ClassRunner.java:250)
at org.junit.runners.BlockJUnit4ClassRunner.createTest(BlockJUnit4ClassRunner.java:260)
at org.junit.runners.BlockJUnit4ClassRunner$2.runReflectiveCall(BlockJUnit4ClassRunner.java:309)
at org.junit.internal.runners.model.ReflectiveCallable.run(ReflectiveCallable.java:12)
at org.junit.runners.BlockJUnit4ClassRunner.methodBlock(BlockJUnit4ClassRunner.java:306)
at org.junit.runners.BlockJUnit4ClassRunner$1.evaluate(BlockJUnit4ClassRunner.java:100)
at org.junit.runners.ParentRunner.runLeaf(ParentRunner.java:366)
at org.junit.runners.BlockJUnit4ClassRunner.runChild(BlockJUnit4ClassRunner.java:103)
at org.junit.runners.BlockJUnit4ClassRunner.runChild(BlockJUnit4ClassRunner.java:63)
at org.junit.runners.ParentRunner$4.run(ParentRunner.java:331)
at org.junit.runners.ParentRunner$1.schedule(ParentRunner.java:79)
at org.junit.runners.ParentRunner.runChildren(ParentRunner.java:329)
at org.junit.runners.ParentRunner.access$100(ParentRunner.java:66)
at org.junit.runners.ParentRunner$2.evaluate(ParentRunner.java:293)
at org.junit.runners.ParentRunner$3.evaluate(ParentRunner.java:306)
at org.junit.runners.ParentRunner.run(ParentRunner.java:413)
at org.junit.runner.JUnitCore.run(JUnitCore.java:137)
at com.intellij.junit4.JUnit4IdeaTestRunner.startRunnerWithArgs(JUnit4IdeaTestRunner.java:69)
at com.intellij.rt.junit.IdeaTestRunner$Repeater$1.execute(IdeaTestRunner.java:38)
at com.intellij.rt.execution.junit.TestsRepeater.repeat(TestsRepeater.java:11)
at com.intellij.rt.junit.IdeaTestRunner$Repeater.startRunnerWithArgs(IdeaTestRunner.java:35)
at com.intellij.rt.junit.JUnitStarter.prepareStreamsAndStart(JUnitStarter.java:235)
at com.intellij.rt.junit.JUnitStarter.main(JUnitStarter.java:54)
Caused by: org.apache.logging.log4j.LoggingException: log4j-slf4j-impl cannot be present with log4j-to-slf4j
at org.apache.logging.slf4j.Log4jLoggerFactory.validateContext(Log4jLoggerFactory.java:49)
at org.apache.logging.slf4j.Log4jLoggerFactory.newLogger(Log4jLoggerFactory.java:39)
at org.apache.logging.slf4j.Log4jLoggerFactory.newLogger(Log4jLoggerFactory.java:30)
at org.apache.logging.log4j.spi.AbstractLoggerAdapter.getLogger(AbstractLoggerAdapter.java:54)
at org.apache.logging.slf4j.Log4jLoggerFactory.getLogger(Log4jLoggerFactory.java:30)
at org.slf4j.LoggerFactory.getLogger(LoggerFactory.java:358)
at org.slf4j.LoggerFactory.getLogger(LoggerFactory.java:383)
at bugs.debug.ParseNettyHttpServerLog.<clinit>(ParseNettyHttpServerLog.java:25)
... 27 more
Process finished with exit code -1
2 问题分析
- 错误日志翻译：
Caused by: org.apache.logging.log4j.LoggingException: log4j-slf4j-impl cannot be present with log4j-to-slf4j
log4j-slf4j-impl 和 log4j-to-slf4j 这两个包不能同时存在。
- 那么为什么这两个包不能同时存在呢？
我们先来看一下这两个包的定义：
- log4j-slf4j-impl ： 主要是 log4j 对
slf4j接口的实现Apache Log4j SLF4J Binding: The Apache Log4j SLF4J API binding to Log4j 2 Core
- log4j-to-slf4j : slf4j 对 log4j 接口的适配
Apache Log4j to SLF4J Adapter: The Apache Log4j binding between Log4j 2 API and SLF4J
这两个接口不能同时存在的意思是说：
要么用 log4j 日志系统，然后同时支持 slf4j 接口的调用；
要么用其他日志系统，比如logback(logback是 slf4j 接口的实现)，然后适配log4j接口。不能兼而有之！
spring boot框架默认使用的logback日志系统，logback实现的是slf4j接口。因此需要适配 log4j 接口，因而会引入log4j-to-slf4j。
因此，如果您正在使用的是spring boot，则不能引入log4j-slf4j-impl。
问题解决思路：只需要看一下是哪个 pom 文件引入了 log4j-slf4j-impl，把这个包去掉就可以啦！
3 解决方法
- 本问题中，博主的工程确实是基于
spring-boot框架，但博主采纳并使用的日志框架是slf4j+log4j
即：需去除
spring-boot自带的log4j-to-slf4j依赖
<dependency>
<groupId>org.springframework.cloud</groupId>
<artifactId>spring-cloud-gateway-server</artifactId>
<scope>test</scope>
<exclusions>
<exclusion>
<artifactId>log4j-to-slf4j</artifactId>
<groupId>org.apache.logging.log4j</groupId>
</exclusion>
</exclusions>
</dependency>