https://github.com/spring-projects/spring-framework: Spring Commons Logging Bridge (Spring IO)
  • Juergen Hoeller 
Spring's variant of the
Commons Logging API: with special support for Log4J 2, SLF4J and java.util.logging. 
This impl package is only present for binary compatibility with existing Commons Logging usage, e.g. in Commons Configuration. NoOpLog can be used as a Log fallback instance, and SimpleLog is not meant to work (issuing a warning when used). 
/**
 * Spring's variant of the
 * <a href="https://commons.apache.org/logging">Commons Logging API</a>:
 * with special support for Log4J 2, SLF4J and {@code java.util.logging}.
 *
 * <p>This {@code impl} package is only present for binary compatibility
 * with existing Commons Logging usage, e.g. in Commons Configuration.
 * {@code NoOpLog} can be used as a {@code Log} fallback instance, and
 * {@code SimpleLog} is not meant to work (issuing a warning when used).
 */
package org.apache.commons.logging.impl;