Avoiding NoClassDefFoundError errors when using slf4j-test with Logback and Maven

As I wrote about in Testing Your SLF4J Logs, the slf4j-test, library is awesome for allowing us to add tests for our logs.

But today I hit a couple of NoClassDefFoundErrors today when setting this up with Logback on a Spring Boot project today, and it was a unobvious how to solve this - so I thought I'd share what fixed it.

Starting with the maven-surefire-plugin configuration as:

<!-- ... -->
<plugin>
  <artifactId>maven-surefire-plugin</artifactId>
  <version>2.22.2</version>
</plugin>
<!-- ... -->

Left me with the usual warnings in my logs, as slf4j-test needs to be the only implementation:

SLF4J: Class path contains multiple SLF4J bindings.
SLF4J: Found binding in [jar:file:/home/jamie/.m2/repository/ch/qos/logback/logback-classic/1.2.3/logback-classic-1.2.3.jar!/org/slf4j/impl/StaticLoggerBinder.class]
SLF4J: Found binding in [jar:file:/home/jamie/.m2/repository/uk/org/lidalia/slf4j-test/1.2.0/slf4j-test-1.2.0.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 [ch.qos.logback.classic.util.ContextSelectorStaticBinder]

I then tried to exclude the logback package from my configuration, and ended up with one of two exceptions:

java.lang.NoClassDefFoundError: ch/qos/logback/classic/turbo/TurboFilter
Caused by: java.lang.ClassNotFoundException: ch.qos.logback.classic.turbo.TurboFilter

Or:

java.lang.NoClassDefFoundError: ch/qos/logback/core/joran/spi/JoranException
Caused by: java.lang.ClassNotFoundException: ch.qos.logback.core.joran.spi.JoranException

It turns out the fix was to exclude both packages:

<!-- ... -->
<plugin>
  <artifactId>maven-surefire-plugin</artifactId>
  <version>2.22.2</version>
  <classpathDependencyExcludes>
    <classpathDependencyExcludes>ch.qos.logback:logback-core</classpathDependencyExcludes>
    <classpathDependencyExcludes>ch.qos.logback:logback-classic</classpathDependencyExcludes>
  </classpathDependencyExcludes>
</plugin>
<!-- ... -->

And then our tests run correctly!

One caveat of this is I've not yet found a way of getting it working so I can use logstash-logback-encoder. This could be related to a Spring Boot defect.

Written by Jamie Tanna's profile image Jamie Tanna on , and last updated on .

Content for this article is shared under the terms of the Creative Commons Attribution Non Commercial Share Alike 4.0 International, and code is shared under the Apache License 2.0.

#blogumentation #testing #java #slf4j.

This post was filed under articles.

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