How to develop a project like trivago, policybazaar etc. in Java

Somebody please help me with my questions.

1. How to develop a website like trivago and policybazaar (a site where I need to compare data/prices)
2. How can I get the data from various sites for comparison? (Let's say that we have three hotels from which I need to fetch the price. How to fetch price from each hotel's website and list all in my website?)
3. Which Java Framework should be used to develop this?
4. Can anybody suggest where I should start?

URGENT

Thanks....