Copyright on files copied from other Open Source project to my Open Source

Question

I'm working on Open Source Java library. I don't want to waste time writing classes that Spring framework already has. I want to copy single files from Spring Framework and refactor it to cut dependencies from whole Spring and connect it with my library.

1. What should I do with copyright information at the beginning of each copied file and comments about authors? Because this files will be refactored, information about authors will be obsolete in future.

2. Should I put information about borrowing files from Spring Framework and original authors in the main LICENSE.txt file?

Answer 1

When copying a file from another project, you must always keep the copyright and license statements intact. At the most, you could change a phrase like "this file is part of project X" into something like "this file was copied from project X and is now part of project Y" and if the copyright statement does not list the names of people, make it clear that the reference is related to project X.
If you make (non-trivial) changes to a copied file, then you could add your name to the copyright statement.

If your code is not distributed under the same license as the Spring Framework, then you must make it clear (this could be in the main LICENSE.txt file) which parts of the code are under which license. There is no need to refer to the original authors here, as that information should be kept in the source files themselves, if it was mentioned there initially.