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From "Wolf, Chris (ELS-CON)" <>
Subject Re: Dependency log4j-slf4j-impl for solr-core:7.5.0 causing a number of build problems
Date Tue, 11 Feb 2020 15:39:27 GMT
(I found this stuck in my outbox, sorry for the delayed response)


Thank you, I finally was able to configure maven to exclude that logging implementation. 
But now I'm having an issue building a Spring-Boot executable WAR with embedded Tomcat, for
some reason, when I "spring-boot:run" it, it seems to use embedded Jetty rather then embedded
Tomcat.  I *think* it's because "solr-core" has transitive dependency on jetty jars.  I will
file a Jira when I get to the bottom of this as well.

Thanks for getting back to me.


On 1/16/20, 10:49 PM, "David Smiley" <> wrote:

    *** External email: use caution ***
    Ultimately if you deduce the problem, file a JIRA issue and share it with
    me; I will look into it.  I care about this matter too; I hate having to
    exclude logging dependencies on the consuming end.
    ~ David Smiley
    Apache Lucene/Solr Search Developer
    On Wed, Jan 15, 2020 at 9:03 PM Wolf, Chris (ELS-CON) <>
    > 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 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:
    >   *   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:
    > …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?

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