java – SLF4J错误：类加载器具有不同类型的类对象

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试图找出为什么我在tomcat日志中收到以下错误： 
Caused by: java.lang.LinkageError: loader constraint violation: when resolving method "org.slf4j.impl.StaticLoggerBinder.getLoggerFactory()Lorg/slf4j/ILoggerFactory;" the class loader (instance of org/apache/catalina/loader/WebappClassLoader) of the current class,org/slf4j/LoggerFactory,and the class loader (instance of sun/misc/Launcher$AppClassLoader) for the method's defining class,org/slf4j/impl/StaticLoggerBinder,have different Class objects for the type org/slf4j/ILoggerFactory used in the signature

在我的gradle文件中,我使用的是slf4j版本1.7.7,在tomcat中我有jul-to-slf4j-1.7.7.jar和slf4j-api-1.7.7.jar,所以我很困惑.

这是堆栈跟踪 – 感谢您的帮助！

Total time: 2.982 secs
Using CATALINA_BASE:   /usr/local/Cellar/tomcat/8.0.18/libexec
Using CATALINA_HOME:   /usr/local/Cellar/tomcat/8.0.18/libexec
Using CATALINA_TMPDIR: /usr/local/Cellar/tomcat/8.0.18/libexec/temp
Using JRE_HOME:        /Library/Java/JavaVirtualMachines/jdk1.8.0_25.jdk/Contents/Home
Using CLASSPATH:       /usr/local/Cellar/tomcat/8.0.18/libexec/bin/jul-to-slf4j-1.7.7.jar:/usr/local/Cellar/tomcat/8.0.18/libexec/bin/slf4j-api-1.7.7.jar:/usr/local/Cellar/tomcat/8.0.18/libexec/bin/logback-classic-1.1.2.jar:/usr/local/Cellar/tomcat/8.0.18/libexec/bin/logback-core-1.1.2.jar:/usr/local/Cellar/tomcat/8.0.18/libexec/bin/logback-config/:/usr/local/Cellar/tomcat/8.0.18/libexec/bin/bootstrap.jar:/usr/local/Cellar/tomcat/8.0.18/libexec/bin/tomcat-juli.jar
19:03:55.979 [main] INFO  org.apache.catalina.startup.VersionLoggerListener - Server version:        Apache Tomcat/8.0.18
19:03:55.981 [main] INFO  org.apache.catalina.startup.VersionLoggerListener - Server built:          Jan 23 2015 11:56:07 UTC
19:03:55.981 [main] INFO  org.apache.catalina.startup.VersionLoggerListener - Server number:         8.0.18.0
19:03:55.982 [main] INFO  org.apache.catalina.startup.VersionLoggerListener - OS Name:               Mac OS X
19:03:55.982 [main] INFO  org.apache.catalina.startup.VersionLoggerListener - OS Version:            10.10
19:03:55.982 [main] INFO  org.apache.catalina.startup.VersionLoggerListener - Architecture:          x86_64
19:03:55.982 [main] INFO  org.apache.catalina.startup.VersionLoggerListener - Java Home:             /Library/Java/JavaVirtualMachines/jdk1.8.0_25.jdk/Contents/Home/jre
19:03:55.982 [main] INFO  org.apache.catalina.startup.VersionLoggerListener - JVM Version:           1.8.0_25-b17
19:03:55.982 [main] INFO  org.apache.catalina.startup.VersionLoggerListener - JVM Vendor:            Oracle Corporation
19:03:55.982 [main] INFO  org.apache.catalina.startup.VersionLoggerListener - CATALINA_BASE:         /usr/local/Cellar/tomcat/8.0.18/libexec
19:03:55.983 [main] INFO  org.apache.catalina.startup.VersionLoggerListener - CATALINA_HOME:         /usr/local/Cellar/tomcat/8.0.18/libexec
19:03:55.983 [main] INFO  org.apache.catalina.startup.VersionLoggerListener - Command line argument: -Djava.util.logging.config.file=/usr/local/Cellar/tomcat/8.0.18/libexec/conf/logging.properties
19:03:55.983 [main] INFO  org.apache.catalina.startup.VersionLoggerListener - Command line argument: -Djava.util.logging.manager=org.apache.juli.ClassLoaderLogManager
19:03:55.983 [main] INFO  org.apache.catalina.startup.VersionLoggerListener - Command line argument: -Djava.endorsed.dirs=/usr/local/Cellar/tomcat/8.0.18/libexec/endorsed
19:03:55.983 [main] INFO  org.apache.catalina.startup.VersionLoggerListener - Command line argument: -Dcatalina.base=/usr/local/Cellar/tomcat/8.0.18/libexec
19:03:55.984 [main] INFO  org.apache.catalina.startup.VersionLoggerListener - Command line argument: -Dcatalina.home=/usr/local/Cellar/tomcat/8.0.18/libexec
19:03:55.984 [main] INFO  org.apache.catalina.startup.VersionLoggerListener - Command line argument: -Djava.io.tmpdir=/usr/local/Cellar/tomcat/8.0.18/libexec/temp
19:03:55.984 [main] INFO  org.apache.catalina.core.AprLifecycleListener - The APR based Apache Tomcat Native library which allows optimal performance in production environments was not found on the java.library.path: /Users/jadekler/Library/Java/Extensions:/Library/Java/Extensions:/Network/Library/Java/Extensions:/System/Library/Java/Extensions:/usr/lib/java:.
19:03:56.076 [main] INFO  org.apache.coyote.http11.Http11NioProtocol - Initializing ProtocolHandler ["http-nio-8080"]
19:03:56.092 [main] INFO  org.apache.tomcat.util.net.NioSelectorPool - Using a shared selector for servlet write/read
19:03:56.094 [main] INFO  org.apache.coyote.ajp.AjpNioProtocol - Initializing ProtocolHandler ["ajp-nio-8009"]
19:03:56.096 [main] INFO  org.apache.tomcat.util.net.NioSelectorPool - Using a shared selector for servlet write/read
19:03:56.096 [main] INFO  org.apache.catalina.startup.Catalina - Initialization processed in 510 ms
19:03:56.115 [main] INFO  org.apache.catalina.core.StandardService - Starting service Catalina
19:03:56.115 [main] INFO  org.apache.catalina.core.StandardEngine - Starting Servlet Engine: Apache Tomcat/8.0.18
19:03:56.132 [localhost-startStop-1] INFO  org.apache.catalina.startup.HostConfig - Deploying web application archive /usr/local/Cellar/tomcat/8.0.18/libexec/webapps/websiteskeleton.war
19:03:56.812 [localhost-startStop-1] ERROR org.apache.catalina.core.StandardContext - Error during ServletContainerInitializer processing
javax.servlet.ServletException: Failed to instantiate WebApplicationInitializer class
    at org.springframework.web.SpringServletContainerInitializer.onStartup(SpringServletContainerInitializer.java:160) ~[spring-web-4.1.0.RELEASE.jar:4.1.0.RELEASE]
    at org.apache.catalina.core.StandardContext.startInternal(StandardContext.java:5143) ~[catalina.jar:8.0.18]
    at org.apache.catalina.util.LifecycleBase.start(LifecycleBase.java:150) [catalina.jar:8.0.18]
    at org.apache.catalina.core.ContainerBase.addChildInternal(ContainerBase.java:725) [catalina.jar:8.0.18]
    at org.apache.catalina.core.ContainerBase.addChild(ContainerBase.java:701) [catalina.jar:8.0.18]
    at org.apache.catalina.core.StandardHost.addChild(StandardHost.java:714) [catalina.jar:8.0.18]
    at org.apache.catalina.startup.HostConfig.deployWAR(HostConfig.java:917) [catalina.jar:8.0.18]
    at org.apache.catalina.startup.HostConfig$DeployWar.run(HostConfig.java:1701) [catalina.jar:8.0.18]
    at java.util.concurrent.Executors$RunnableAdapter.call(Executors.java:511) [na:1.8.0_25]
    at java.util.concurrent.FutureTask.run(FutureTask.java:266) [na:1.8.0_25]
    at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1142) [na:1.8.0_25]
    at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:617) [na:1.8.0_25]
    at java.lang.Thread.run(Thread.java:745) [na:1.8.0_25]
Caused by: java.lang.LinkageError: loader constraint violation: when resolving method "org.slf4j.impl.StaticLoggerBinder.getLoggerFactory()Lorg/slf4j/ILoggerFactory;" the class loader (instance of org/apache/catalina/loader/WebappClassLoader) of the current class,have different Class objects for the type org/slf4j/ILoggerFactory used in the signature
    at org.slf4j.LoggerFactory.getILoggerFactory(LoggerFactory.java:306) ~[slf4j-api-1.7.7.jar:1.7.7]
    at org.slf4j.LoggerFactory.getLogger(LoggerFactory.java:276) ~[slf4j-api-1.7.7.jar:1.7.7]
    at org.slf4j.LoggerFactory.getLogger(LoggerFactory.java:288) ~[slf4j-api-1.7.7.jar:1.7.7]
    at com.websiteskeleton.core.HelloInitializer.<init>(HelloInitializer.java:13) ~[HelloInitializer.class:na]
    at sun.reflect.NativeConstructorAccessorImpl.newInstance0(Native Method) ~[na:1.8.0_25]
    at sun.reflect.NativeConstructorAccessorImpl.newInstance(NativeConstructorAccessorImpl.java:62) ~[na:1.8.0_25]
    at sun.reflect.DelegatingConstructorAccessorImpl.newInstance(DelegatingConstructorAccessorImpl.java:45) ~[na:1.8.0_25]
    at java.lang.reflect.Constructor.newInstance(Constructor.java:408) ~[na:1.8.0_25]
    at java.lang.Class.newInstance(Class.java:438) ~[na:1.8.0_25]
    at org.springframework.web.SpringServletContainerInitializer.onStartup(SpringServletContainerInitializer.java:157) ~[spring-web-4.1.0.RELEASE.jar:4.1.0.RELEASE]
    ... 12 common frames omitted
19:03:56.821 [localhost-startStop-1] ERROR org.apache.catalina.core.StandardContext - Context [/websiteskeleton] startup Failed due to prevIoUs errors
19:03:56.825 [localhost-startStop-1] INFO  org.apache.catalina.startup.HostConfig - Deployment of web application archive /usr/local/Cellar/tomcat/8.0.18/libexec/webapps/websiteskeleton.war has finished in 693 ms
19:03:56.826 [localhost-startStop-1] INFO  org.apache.catalina.startup.HostConfig - Deploying web application directory /usr/local/Cellar/tomcat/8.0.18/libexec/webapps/docs
19:03:56.893 [localhost-startStop-1] INFO  org.apache.jasper.servlet.TldScanner - At least one JAR was scanned for TLDs yet contained no TLDs. Enable debug logging for this logger for a complete list of JARs that were scanned but no TLDs were found in them. Skipping unneeded JARs during scanning can improve startup time and JSP compilation time.
19:03:56.904 [localhost-startStop-1] INFO  org.apache.catalina.startup.HostConfig - Deployment of web application directory /usr/local/Cellar/tomcat/8.0.18/libexec/webapps/docs has finished in 78 ms
19:03:56.904 [localhost-startStop-1] INFO  org.apache.catalina.startup.HostConfig - Deploying web application directory /usr/local/Cellar/tomcat/8.0.18/libexec/webapps/examples
19:03:57.133 [localhost-startStop-1] INFO  org.apache.catalina.startup.HostConfig - Deployment of web application directory /usr/local/Cellar/tomcat/8.0.18/libexec/webapps/examples has finished in 228 ms
19:03:57.133 [localhost-startStop-1] INFO  org.apache.catalina.startup.HostConfig - Deploying web application directory /usr/local/Cellar/tomcat/8.0.18/libexec/webapps/host-manager
19:03:57.192 [localhost-startStop-1] INFO  org.apache.jasper.servlet.TldScanner - At least one JAR was scanned for TLDs yet contained no TLDs. Enable debug logging for this logger for a complete list of JARs that were scanned but no TLDs were found in them. Skipping unneeded JARs during scanning can improve startup time and JSP compilation time.
19:03:57.195 [localhost-startStop-1] INFO  org.apache.catalina.startup.HostConfig - Deployment of web application directory /usr/local/Cellar/tomcat/8.0.18/libexec/webapps/host-manager has finished in 62 ms
19:03:57.195 [localhost-startStop-1] INFO  org.apache.catalina.startup.HostConfig - Deploying web application directory /usr/local/Cellar/tomcat/8.0.18/libexec/webapps/manager
19:03:57.252 [localhost-startStop-1] INFO  org.apache.jasper.servlet.TldScanner - At least one JAR was scanned for TLDs yet contained no TLDs. Enable debug logging for this logger for a complete list of JARs that were scanned but no TLDs were found in them. Skipping unneeded JARs during scanning can improve startup time and JSP compilation time.
19:03:57.254 [localhost-startStop-1] INFO  org.apache.catalina.startup.HostConfig - Deployment of web application directory /usr/local/Cellar/tomcat/8.0.18/libexec/webapps/manager has finished in 59 ms
19:03:57.254 [localhost-startStop-1] INFO  org.apache.catalina.startup.HostConfig - Deploying web application directory /usr/local/Cellar/tomcat/8.0.18/libexec/webapps/ROOT
19:03:57.307 [localhost-startStop-1] INFO  org.apache.jasper.servlet.TldScanner - At least one JAR was scanned for TLDs yet contained no TLDs. Enable debug logging for this logger for a complete list of JARs that were scanned but no TLDs were found in them. Skipping unneeded JARs during scanning can improve startup time and JSP compilation time.
19:03:57.308 [localhost-startStop-1] INFO  org.apache.catalina.startup.HostConfig - Deployment of web application directory /usr/local/Cellar/tomcat/8.0.18/libexec/webapps/ROOT has finished in 54 ms
19:03:57.310 [main] INFO  org.apache.coyote.http11.Http11NioProtocol - Starting ProtocolHandler ["http-nio-8080"]
19:03:57.314 [main] INFO  org.apache.coyote.ajp.AjpNioProtocol - Starting ProtocolHandler ["ajp-nio-8009"]
19:03:57.315 [main] INFO  org.apache.catalina.startup.Catalina - Server startup in 1218 ms

解决方法

Tomcat日志显示类路径上有另一个slf4j-1.7.7.jar：

使用CLASSPATH：/usr/local/Cellar/tomcat/8.0.18/libexec/bin/jul-to-slf4j-1.7.7.jar:/usr/local/Cellar/tomcat/8.0.18/libexec/bin/slf4j -API-1.7.7.jar：/usr/local/Cellar/tomcat/8.0.18/libexec/bin/logback-classic-1.1.2.jar：/usr/local/Cellar/tomcat/8.0.18/libexec /bin/logback-core-1.1.2.jar:/usr/local/Cellar/tomcat/8.0.18/libexec/bin/logback-config/:/usr/local/Cellar/tomcat/8.0.18/libexec/斌/ bootstrap.jar：/usr/local/Cellar/tomcat/8.0.18/libexec/bin/tomcat-juli.jar

初始化Tomcat时,它会初始化jul-to-slf4j和slf4j-api.这些jar正由Classloader加载,它装载了Tomcat jar(sun / misc / Launcher $AppClassLoader).

当您的应用程序尝试访问slf4j-api类时,它使用WebApplication类加载器(org / apache / catalina / loader / WebappClassLoader),它默认在系统类路径之前在app类路径上搜索类定义.请注意,这可以更改：https://tomcat.apache.org/tomcat-8.0-doc/class-loader-howto.html

在Java中,类签名由类完全限定名和加载类的类加载器组成.如果一个类从两个不同的类加载器(相同的层次结构)加载两次,那么JVM将有两个不同的类.尝试将一个类的对象引用指向另一个类的变量将显示ClassCastException.查看此博客文章(第5项)以获取更多信息：https://techblug.wordpress.com/2012/03/17/classloader-tips/

所以,据我所知,你可以通过从Tomcat类路径中删除slf4j – * .jar来解决这个问题,或者如果你有多个使用相同版本的slf4j的webapp,你可以从webapp中删除jar,所以它将使用Tomcat类加载器加载的那些.

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