Exception in thread "main" java.lang.IllegalAccessError: tried to access field
org.slf4j.impl.StaticLoggerBinder.SINGLETON from class org.slf4j.LoggerFactory
at org.slf4j.LoggerFactory.<clinit>(LoggerFactory.java:60)
Googling led me to the SLF4J FAQ (http://www.slf4j.org/faq.html) which says that this is caused by slf4j-api <= 1.5.5 being incompatible with an slf4j binding > 1.5.5. My application declares slf4j-api 1.5.8 and slf4j-log4j12 1.5.8 as dependencies. Running mvn dependency:tree didn't reveal any slf4j-api <= 1.5.5, but, indeed, in WEB-INF/lib in the application's war-file there was a slf4j-api-1.5.2.jar. Where did it come from?
When running mvn package with the log level of Ivy resolver set to "info", it seems that it was pulled in by Hibernate, through its dependencies hibernate-core and hibernate-commons-annotations. Problem solved! Grails has great support for determining which of the plugin's dependencies to exclude. In the Grails Reference Documentation it says:
If a plugin is using a JAR which conflicts with another plugin, or an application dependency then you can override how a plugin resolves its dependencies inside an application using exclusions. For example:
plugins {
runtime( "org.grails.plugins:hibernate:1.3.0" ) {
excludes "javassist"
}
}
This means that all I have to do is include the following in my BuildConfig.groovy:
runtime("org.grails.plugins:hibernate:1.3.7") {
excludes "slf4j-api"
}
No luck. slf4j-api-1.5.2.jar was still there. Googling suggested that there is a bug in Grails that prevents it from excluding transitive dependencies of plugins (GRAILS-6910). Allright. Let me exclude hibernate-core and hibernate-comons-annotations, then, and include them as dependencies with slf4j-api excluded, ie.
dependencies {
compile("org.hibernate:hibernate-commons-annotations:3.1.0.GA") {
excludes "slf4j-api"
}
compile("org.hibernate:hibernate-core:3.1.0.GA") {
excludes "slf4j-api"
}
}plugins {
runtime("org.grails.plugins:hibernate:1.3.7") {
excludes "hibernate-core", "hibernate-commons-annotations"
}
}Still no luck.
Finally, Google led me to this page: Excluding files from a WAR with Grails – the right way. There, Marc Palmer suggested adding the following to Config.groovy to exclude a certain .jar-file from the war file:
grails.war.resources = { stagingDir ->
delete(file:"${stagingDir}/WEB-INF/lib/slf4j-api-1.5.2.jar")
}
Ran mvn package while I held my breath. Once finished, I checked the generated war file, and, to my disappointment, the slf4j-api-1.5.2.jar was still there.
However, reading through the mentioned post's comments, some guy suggested that it should be added to BuildConfig.groovy, rather than Config.groovy.
Tried that. And finally, no slf4j-api-1.5.2.jar in the generated war file, only my own slf4j-api-1.5.8.jar.
Deployed the war to Jetty, and it worked like a charm.
It seems to me that Grails' dependency manipulation methods are rather buggy at the moment. I find this an acceptable workaround.
