SLF4J errore: class loader hanno oggetti di classe differenti per il tipo

Question

cercando di capire il motivo per cui sto ottenendo il seguente errore nel log di Tomcat:

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 

Nei miei file Gradle sto usando slf4j versione 1.7. 7, e in tomcat ho jul-to-slf4j-1.7.7.jar e slf4j-api-1.7.7.jar, quindi sono abbastanza confuso.

Ecco la traccia dello stack: grazie per qualsiasi aiuto!

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$Worker.run(ThreadPoolExecutor.java:617) [na:1.8.0_25] 
    at java.lang.Thread.run(Thread.java:745) [na:1.8.0_25] 
Caused by: java.lang.LinkageError: loader constraint violation: when resolving method "org.slf4j.impl.StaticLoggerBinder.getLoggerFactory()Lorg/slf4j/ILoggerFactory;" the class loader (instance of org/apache/catalina/loader/WebappClassLoader) of the current class, org/slf4j/LoggerFactory, and the class loader (instance of sun/misc/Launcher$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 
    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 

Answer 1

registro

Il Tomcat mostra si dispone di un'altra slf4j-1.7.7.jar nel classpath:

Utilizzando 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/Cantina /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

Quando Tomcat è stato inizializzato, inizializza jul-to-slf4j e slf4j-api. Questi jar sono stati caricati dal Classloader che caricava i jar Tomcat (sun/misc/Launcher $ AppClassLoader).

Quando l'applicazione tenta di accedere alle classi slf4j-api, utilizza il Classloader WebApplication (org/apache/catalina/loader/WebappClassLoader), che per impostazione predefinita cerca la definizione di classi sul percorso di classe dell'app prima del classpath di sistema. Nota che può essere modificato: https://tomcat.apache.org/tomcat-8.0-doc/class-loader-howto.html

In Java, la firma della classe è composta dal nome completo completo della classe e dal classloader che ha caricato la classe. Se una classe viene caricata due volte da due diversi classloader (stessa gerarchia), ci saranno due classi diverse per la JVM. Provare a puntare un riferimento a un oggetto di una classe a una variabile dell'altra tromerà una ClassCastException. Controllare questo post del blog (elemento 5) per ulteriori informazioni su questo: https://techblug.wordpress.com/2012/03/17/classloader-tips/

Quindi, per quanto ne so, è possibile risolvere questo rimuovendo il jar slf4j - *. Dal classpath Tomcat, o se si dispone di più una webapp che utilizza la stessa versione di slf4j, è possibile rimuovere i jar dalla webapp, quindi userà quelli caricati dal classloader Tomcat.