What is "inventing a new wheel "?

Recently, when I read some technical articles, I often see a sentence called "inventing a new wheel" (as if it was in J2EE WithOut EJB for the first time, then I saw it in some technical documents and the latest issue of programmer magazine.) I never quite understood what he meant.

I was bored when I waited at the subway station yesterday. So I rummaged through books in the bookstore and saw this sentence in a book about personnel management.
After reading it, it seems like a foreign saying or something like that the wheel of a car has long been invented, but it has been invented by itself. It should be used to describe repeated unnecessary work.

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