Eclipse error: "The import XXX cannot be resolved"

Clean the project. And double-check the jars being really on the build path (with no errors). Also make sure there is nothing in the "Problems" view.

Try cleaning your project by going to the following menu item:

Project > Clean...

If that doesn't work, try removing the jars from the build path and adding them again.

Obviously there are cases where there is a valid issue however Eclipse throws this error for no good reason sometimes. This is still (in v 2020-09) an old (2010) Eclipse bug that can be resolved by making a negligible change to the project settings.

touch .classpath

solves the issue, or go to Project > Properties > Java Build Path > Order and Export > make a meaningless order change > Apply. Changing the order back does not regress to the problem.

If is a Maven project, also click on Maven >> Update project... (F5)