Multiple SLF4J Bindings Error

Error

SLF4J: Class path contains multiple SLF4J bindings.
SLF4J: Found binding in [jar:file:/path/to/jar!/org/slf4j/impl/StaticLoggerBinder.class]
SLF4J: Found binding in [jar:file:/path/to/another/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]

Solution

Case A: exclusion

• Project X -> Project Y -> Project A

in Project X, when declaring Project Y as dependency, explicitly exclude Project A

Add exclusions to dependency in pom

<dependencies>
    <dependency>
        <groupId> org.apache.cassandra</groupId>
        <artifactId>cassandra-all</artifactId>
        <version>0.8.1</version>

        <exclusions>
            <exclusion>
                <groupId>org.slf4j</groupId>
                <artifactId>slf4j-log4j12</artifactId>
            </exclusion>
            <exclusion>
                <groupId>log4j</groupId>
                <artifactId>log4j</artifactId>
            </exclusion>
        </exclusions>

    </dependency>
</dependencies>

Case B: optional

• Project X
  • -> Project Y -> Project A
  • -> Project Z -> Project A
  • -> Project A

in Project Y/Z' pom, set Project A as optional, then it will not be included in the classpath

<dependency>
    <groupId>org.slf4j</groupId>
    <artifactId>slf4j-log4j12</artifactId>
    <version>1.7.7</version>
    <optional>true</optional>
</dependency>

Case C: provided

• Project X -> Project A
• Project Y -> Project A
• Project Z -> Project A

And X Y Z are all in classpath: set all but 1 to <scope>provided</scope>

<dependency>
    <groupId>org.slf4j</groupId>
    <artifactId>slf4j-log4j12</artifactId>
    <version>1.7.7</version>
    <optional>true</optional>
    <scope>provided</scope>
</dependency>