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You can open an existing Maven project using File -> Open Project. Valid folders will have a yellow box in the lower right of the folder icon. For instance, I could choose the GeomConverter or lcsim folders below.
Select one a valid folder in the chooser window and click Open Project Folder.
Netbeans will now scan the project for classes and the like, which takes awhile. Once it is finished, you should see the project in the lefthand window.
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