【解决】SLF4J: Class path contains multiple SLF4J bindings.

在启动springboot项目时，遇到了这个问题，上网查询多个方案，最终这个方法得到解决

问题描述：

SLF4J: Class path contains multiple SLF4J bindings.
SLF4J: Found binding in [jar:file:/D:/Program%20Files/JavaEclipse/repo/ch/qos/logback/logback-classic/1.2.3/logback-classic-1.2.3.jar!/org/slf4j/impl/StaticLoggerBinder.class]
SLF4J: Found binding in [jar:file:/D:/Program%20Files/JavaEclipse/repo/org/slf4j/slf4j-log4j12/1.7.25/slf4j-log4j12-1.7.25.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 [ch.qos.logback.classic.util.ContextSelectorStaticBinder]
Logging system failed to initialize using configuration from 'classpath:log4j.properties'
java.lang.IllegalStateException: Could not initialize Logback logging from classpath:log4j.properties
	at org.springframework.boot.logging.logback.LogbackLoggingSystem.loadConfiguration(LogbackLoggingSystem.java:156)
	at org.springframework.boot.logging.AbstractLoggingSystem.initializeWithSpecificConfig(AbstractLoggingSystem.java:67)
	at org.springframework.boot.logging.AbstractLoggingSystem.initialize(AbstractLoggingSystem.java:57)
	at org.springframework.boot.logging.logback.LogbackLoggingSystem.initialize(LogbackLoggingSystem.java:117)
	at org.springframework.boot.context.logging.LoggingApplicationListener.initializeSystem(LoggingApplicationListener.java:295)
	at org.springframework.boot.context.logging.LoggingApplicationListener.initialize(LoggingApplicationListener.java:263)
	at org.springframework.boot.context.logging.LoggingApplicationListener.onApplicationEnvironmentPreparedEvent(LoggingApplicationListener.java:226)
	at org.springframework.boot.context.logging.LoggingApplicationListener.onApplicationEvent(LoggingApplicationListener.java:199)
	at org.springframework.context.event.SimpleApplicationEventMulticaster.doInvokeListener(SimpleApplicationEventMulticaster.java:172)
	at org.springframework.context.event.SimpleApplicationEventMulticaster.invokeListener(SimpleApplicationEventMulticaster.java:165)
	at org.springframework.context.event.SimpleApplicationEventMulticaster.multicastEvent(SimpleApplicationEventMulticaster.java:139)
	at org.springframework.context.event.SimpleApplicationEventMulticaster.multicastEvent(SimpleApplicationEventMulticaster.java:127)
	at org.springframework.boot.context.event.EventPublishingRunListener.environmentPrepared(EventPublishingRunListener.java:75)
	at org.springframework.boot.SpringApplicationRunListeners.environmentPrepared(SpringApplicationRunListeners.java:54)
	at org.springframework.boot.SpringApplication.prepareEnvironment(SpringApplication.java:347)
	at org.springframework.boot.SpringApplication.run(SpringApplication.java:306)
	at org.springframework.boot.SpringApplication.run(SpringApplication.java:1260)
	at org.springframework.boot.SpringApplication.run(SpringApplication.java:1248)
	at com.example.demo.DemoApplication.main(DemoApplication.java:12)
Caused by: ch.qos.logback.core.LogbackException: Unexpected filename extension of file [file:/F:/spingboot/onepiece/target/classes/log4j.properties]. Should be either .groovy or .xml
	at ch.qos.logback.classic.util.ContextInitializer.configureByResource(ContextInitializer.java:77)
	at org.springframework.boot.logging.logback.LogbackLoggingSystem.configureByResourceUrl(LogbackLoggingSystem.java:183)
	at org.springframework.boot.logging.logback.LogbackLoggingSystem.loadConfiguration(LogbackLoggingSystem.java:152)

原因分析：

logback-classic 包和slf4j-log4j12 包，关于org/slf4j/impl/StaticLoggerBinder.class 这个类发生了冲突。其实就是logback和log4j之间的冲突。

这是因为springboot的默认日志是logback，log4j在之前是主流日志，很多第三方工具包都引入了log4j，而我们在开发时会引入很多第三方包，这就造成了冲突。

问题解决：排除其中一个的依赖

如果使用的是log4j的日志，则只需排序logback的依赖即可。

在spring-boot-starter 和 spring-boot-starter-web两个依赖中添加如下内容，排除logback依赖
切记：两个依赖中都需要进行排除

       <!-- SpringBoot 依赖-->
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-aop</artifactId>
        </dependency>
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter</artifactId>
            <exclusions>
                <!-- 排除自带的logback依赖 -->
                <exclusion>
                    <groupId>org.springframework.boot</groupId>
                    <artifactId>spring-boot-starter-logging</artifactId>
                </exclusion>
            </exclusions>
        </dependency>
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-web</artifactId>
            <exclusions>
                <!-- 排除自带的logback依赖 -->
                <exclusion>
                    <groupId>org.springframework.boot</groupId>
                    <artifactId>spring-boot-starter-logging</artifactId>
                </exclusion>
            </exclusions>
        </dependency>