How can I do date format convertion?

Hi, I have a list of date like

20150204
20150304
20150309
20150323
20150331
20150416
20150608

I would like to change it to

2015.02.04
2015.03.04
2015.03.09
2015.03.23
2015.03.31
2015.04.16
2015.06.08

How can I do that?

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