Override runtime SLF4J binding for test

user_139909 0
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I am writing a package. I need slf4j-log4j12 with specific appender for runtime. But for tests, I just need a slf4j-simple binding. So, my pom.xml looks like this:

<?xml version="1.0" encoding="UTF-8"?>
<project xmlns="http://maven.apache.org/POM/4.0.0"
         xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
         xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
    <modelVersion>4.0.0</modelVersion>

    <properties>
        <maven.compiler.target>1.8</maven.compiler.target>
        <maven.compiler.source>1.8</maven.compiler.source>
    </properties>

    <groupId>com.bharani</groupId>
    <artifactId>LoggingDemo</artifactId>
    <version>1.0-SNAPSHOT</version>

    <dependencies>
        <!-- Direct dependencies -->
        <!-- https://mvnrepository.com/artifact/org.slf4j/slf4j-api -->
        <dependency>
            <groupId>org.slf4j</groupId>
            <artifactId>slf4j-api</artifactId>
            <version>1.7.25</version>
        </dependency>
        <!-- https://mvnrepository.com/artifact/org.slf4j/slf4j-log4j12 -->
        <dependency>
            <groupId>org.slf4j</groupId>
            <artifactId>slf4j-log4j12</artifactId>
            <version>1.7.25</version>
            <scope>runtime</scope>
        </dependency>

        <!-- Test dependencies -->
        <!-- https://mvnrepository.com/artifact/junit/junit -->
        <dependency>
            <groupId>junit</groupId>
            <artifactId>junit</artifactId>
            <version>4.12</version>
            <scope>test</scope>
        </dependency>
        <!-- https://mvnrepository.com/artifact/org.assertj/assertj-core -->
        <dependency>
            <groupId>org.assertj</groupId>
            <artifactId>assertj-core</artifactId>
            <version>3.8.0</version>
            <scope>test</scope>
        </dependency>
        <!-- https://mvnrepository.com/artifact/org.slf4j/slf4j-simple -->
        <dependency>
            <groupId>org.slf4j</groupId>
            <artifactId>slf4j-simple</artifactId>
            <version>1.7.25</version>
            <scope>test</scope>
        </dependency>
    </dependencies>

</project>

When I run my program, I get log4j logs as expected. But when I run tests, I get:

SLF4J: Class path contains multiple SLF4J bindings.
SLF4J: Found binding in [jar:file:/Users/bharani/.m2/repository/org/slf4j/slf4j-log4j12/1.7.25/slf4j-log4j12-1.7.25.jar!/org/slf4j/impl/StaticLoggerBinder.class]
SLF4J: Found binding in [jar:file:/Users/bharani/.m2/repository/org/slf4j/slf4j-simple/1.7.25/slf4j-simple-1.7.25.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.slf4j.impl.Log4jLoggerFactory]

...and I don't see logs in Console as expected out of slf4j-simple binding.

How do I resolve this? How can keep runtime dependency on slf4j-log4j12 away from tests?

Thanks.

slf4j maven java
1 Answers

The problem is that a dependency of scope runtime is also included in the test classpath, so SLF4J ends up having two bindings and has to pick one of them (the binding it chooses is likely random, it happened that it picked log4j in your case).

A simple solution is to remove the log4j binding from the classpath of the Surefire plugin:

<build>
  <plugins>
    <plugin>
      <groupId>org.apache.maven.plugins</groupId>
      <artifactId>maven-surefire-plugin</artifactId>
      <version>2.20.1</version>
      <configuration>
        <classpathDependencyExcludes>
          <classpathDependencyExcludes>org.slf4j:slf4j-log4j12</classpathDependencyExcludes>
        </classpathDependencyExcludes>
      </configuration>
    </plugin>
  </plugins>
</build>

More info in http://maven.apache.org/surefire/maven-surefire-plugin/examples/configuring-classpath.html.

user_10642450
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