Are you also having the same error?

Solution

This happens when MW_HOME is not defined and weblogic.jar is getting called twice in CLASSPATH. To fix this, check below two points.

Ensure weblogic.jar in CLASSPATH is not duplicated. You can check CLASSPATH section when it prints while starting. Set MW_HOME either on Unix shell or in startup scripts.

Start Oracle WebLogic now, it should work!