Combining websites

hello

I was wondering if there is a framework for combining different websites.

I have got seperate standalone websites a, b, c, d that I want to merge into one portal and make it look like one website.

Is there a best practice way to do this in java ?

I know I could just have used iframe or frame and be done but I want to make it look seamless and one css for everything.
I do not have access to do changes to the websites that I am combining.

So how should I grab the html from the pages and insert them into divs and apply my own css in an elegant way ?

Thank you