Is Log4j being abandoned in favor of Slf4j?

Slf4j is indeed just a logging facade. However, Log4j is intended to be succeeded by Logback, from the very same authors.

Update: if you'd like to know about another benefit of Slf4j, it's the fact that following (ugly) constructs aren't needed anymore to avoid the toString() unnecessarily been called:

if (logger.isDebugEnabled()) {
    logger.debug("Message: " + bigObject + ", " + anotherBigObject);
}

You can instead make use of parameterized messages:

logger.debug("Message: {}, {}", bigObject, anotherBigObject);

Also see What is the fastest way of (not) logging?

Slf4J is not an alternative for Log4j, but rather provides a Façade for logging, so one can you can plug in your own logging framework. It's mainly useful for libraries. from slf4j.org:

The Simple Logging Facade for Java or (SLF4J) serves as a simple facade or abstraction for various logging frameworks, e.g. java.util.logging, log4j and logback, allowing the end user to plug in the desired logging framework at deployment time.

To answer your question: Slf4j is being adopted by frameworks now, but in your projects, you can keep on using Log4J (or any other)