（1）问题描述

在Spring Boot基础之上，集成Spring Security框架的时候，启动项目报错：

Caused by: org.apache.logging.log4j.LoggingException: log4j-slf4j-impl cannot be present with log4j-to-slf4j

报错内容如下：

SLF4J: Class path contains multiple SLF4J bindings.
SLF4J: Found binding in [jar:file:/E:/softwares/MavenRepository/org/apache/logging/log4j/log4j-slf4j-impl/2.17.2/log4j-slf4j-impl-2.17.2.jar!/org/slf4j/impl/StaticLoggerBinder.class]
SLF4J: Found binding in [jar:file:/E:/softwares/MavenRepository/ch/qos/logback/logback-classic/1.2.11/logback-classic-1.2.11.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]
Exception in thread "main" java.lang.ExceptionInInitializerError
	at com.gitee.demo.Application.main(Application.java:17)
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:60)
	at org.apache.logging.slf4j.Log4jLoggerFactory.newLogger(Log4jLoggerFactory.java:44)
	at org.apache.logging.slf4j.Log4jLoggerFactory.newLogger(Log4jLoggerFactory.java:33)
	at org.apache.logging.log4j.spi.AbstractLoggerAdapter.getLogger(AbstractLoggerAdapter.java:53)
	at org.apache.logging.slf4j.Log4jLoggerFactory.getLogger(Log4jLoggerFactory.java:33)
	at org.slf4j.LoggerFactory.getLogger(LoggerFactory.java:363)
	at org.apache.commons.logging.LogAdapter$Slf4jAdapter.createLocationAwareLog(LogAdapter.java:130)
	at org.apache.commons.logging.LogAdapter.createLog(LogAdapter.java:91)
	at org.apache.commons.logging.LogFactory.getLog(LogFactory.java:67)
	at org.apache.commons.logging.LogFactory.getLog(LogFactory.java:59)
	at org.springframework.boot.SpringApplication.<clinit>(SpringApplication.java:174)
	... 1 more

（2）解决方案

出现上面报错的原因是：

• 引入的【log4j2】依赖和Spring中的【logging】日志依赖发生冲突。

解决办法：

• 排除Spring中自带的logging日志依赖。
• 两个地方需要排除
  • 【spring-boot-starter-web】依赖
  • 【spring-boot-starter-security】依赖

我是因为引入了【spring-boot-starter-security】依赖，但是没有将logging依赖排除，所以启动时候提示：log4j-slf4j-impl cannot be present with log4j-to-slf4j。

<!-- web工程依赖 -->
<dependency>
    <groupId>org.springframework.boot</groupId>
    <artifactId>spring-boot-starter-web</artifactId>
    <!-- 排除SpringBoot自带的日志依赖 -->
    <exclusions>
        <exclusion>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-logging</artifactId>
        </exclusion>
    </exclusions>
</dependency>
<!-- 引入 spring security 安全框架依赖 -->
<dependency>
    <groupId>org.springframework.boot</groupId>
    <artifactId>spring-boot-starter-security</artifactId>
    <!-- 排除SpringBoot自带的日志依赖 -->
    <exclusions>
        <exclusion>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-logging</artifactId>
        </exclusion>
    </exclusions>
</dependency>
<!-- 引入 log4j2 依赖, 版本和SpringBoot一致 -->
<dependency>
    <groupId>org.springframework.boot</groupId>
    <artifactId>spring-boot-starter-log4j2</artifactId>
</dependency>

以上，就是log4j2日志依赖冲突的问题原因及解决方案。