How to convert jsp page to text file ?

They are. The question is answered. Next!
—SA

You download it first, then you can use a text editor to look at it.

It won't be downloaded, only generated HTML (typically) will. But OP can get it on the server side. But why?
The question doesn't make sense.
—SA

JSP is running on server side. When you open the JSP pages in Web browser, they've already been interpreted to pure HTML content. Of course you can download and save the files to any text files, and yet you can't get the logic behind that.