This dependency is the api:
<dependency>
<groupId>org.slf4j</groupId>
<artifactId>slf4j-api</artifactId>
<version>1.7.5</version>
</dependency>
You need the slf4j-api.jar in your classpath for compiling, not the slf4j-log4j12.jar.
It worked in maven because the binding-lib (slf4j-log4j12) has a dependency on the api and thus maven loads that as well, without you explicitly defining it as a dependency.