How do I identify the association of new file types (files types) in eclipse?

During this time, due to project needs, the. btl file type is used instead of the. jsp file type for the front-end page interaction, but Eclipse does not recognize the. btl file type. So you need to do the following:

1.Window->preference Search File->file Associations

2.Add a file type (for example: Add->.btl)

3. after the sixth step, continue

4. after saving, return to the interface to see the. btl file, which has been identified by eclipse in. JSP mode.

How do I identify the association of new file types (files types) in eclipse?