I am having several issues due to the slf4j implementation dependency “log4j-slf4j-impl” being declared as a dependency of solr-core:7.5.0. The first issue observed when starting the app is this:
SLF4J: Class path contains multiple SLF4J bindings. SLF4J: Found binding in [jar:file:/Users/ma-wolf2/.m2/repository/org/apache/logging/log4j/log4j-slf4j-impl/2.7/log4j-slf4j-impl-2.7.jar!/org/slf4j/impl/StaticLoggerBinder.class] SLF4J: Found binding in [jar:file:/Users/ma-wolf2/.m2/repository/ch/qos/logback/logback-classic/1.1.3/logback-classic-1.1.3.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] I first got wind that this might not be just myself from this thread: https://lucene.472066.n3.nabble.com/log4j-slf4j-impl-dependency-in-solr-core-td4449635.html#a4449891 * If there are any users that integrate solr-core into their own code, it's currently a bit of a land-mine situation to change logging implementations. If there's a way we can include log4j jars at build time, but remove the log4j dependency on the published solr-core artifact, that might work well. We should do our best to make it so people can use EmbeddedSolrServer without log4j jars. There are two dimensions to this dependency problem: * Building a war file (this runs with a warning) * Building a spring-boot executable JAR with embedded servlet container (doesn’t run) When building a WAR and deploying, I get the “multiple SLF4J bindings” warning, but the app works. However, I want the convenience of a spring-boot executable JAR with embedded servlet container, but in that case, I get that warning followed by a fatal NoClassDefFoundError/ ClassNotFoundException – which is a show-stopper. If I hack the built spring-boot FAT jar and remove “log4j-slf4j-impl.jar” then the app works. For the WAR build, the proper version of log4j-slf4j-impl.jar was included – 2.11.0, but,for some reason when building the spring-boot fat (uber) jar, it was building with log4j-slf4j-impl:2.7 so of course it will croak. There are several issues: 1. I don’t want log4j-slf4j-impl at all 2. Somehow the version of “log4j-slf4j-impl” being used for the build is 2.7 rather then the expected 2.11.0 3. Due to the version issue, the app croaks with ClassNotFoundException: org.apache.logging.log4j.util.ReflectionUtil For issue #1, I tried: <dependency> <groupId>org.apache.solr</groupId> <artifactId>solr-core</artifactId> <version>7.5.0</version> <exclusions> <exclusion> <artifactId>org.apache.logging.log4j</artifactId> <groupId>log4j-slf4j-impl</groupId> </exclusion> </exclusions> </dependency> All to no avail, as that dependency ends up in the packaged build - for WAR, it’s version 2.11.0, so even though it’s a bad build, the app runs, but for building a spring-boot executable JAR with embedded webserver, for some reason, it switches log4j-slf4j-impl from version 2.11.0 to 2,7 (2.11.0 works, but should not even be there) I also tried this: https://docs.spring.io/spring-boot/docs/current/maven-plugin/examples/exclude-dependency.html …that didn’t work either. I’m thinking that solr-core should have added a classifier of “provided” for “log4j-slf4j-impl”, but that’s conjecture of a possible solution going forward, but does anyone know how I can exclude “log4j-slf4j-impl” from a spring-boot build?
