The FacesContext class isn't in your webapp's classpath. Depending on which version of WebLogic you're running, that may mean you need to explicitly include a jsf-impl.jar in your WAR. Alternatively, you may have classpath conflicts if you have included a jsf-impl.jar but the version of WebLogic you're running has its own JSF implementation classes.
It doesn't have anything to do with the ELResolver.
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