present perfect - "have been working" vs. "have worked"

What is the difference between the following two sentences?

1. I have been working here for 20 years.


2. I have worked here for 20 years.

The present perfect tense is used for repetitive or constant actions that began in the past and continue to the present. The perfect progressive tense is used for continuous actions that began in the past and continue to the present. But I really don't see the difference here.