How to transform PageRequest object to query string?

I'm writing an RESTful API which consumes another RESTful Data API, and I'm using Spring Data.

The client side send the page request using query params like:
http://api.mysite.com/products?page=1&size=20&sort=id,asc&sort=name,desc

And I transform the params to PageRequest object and transfer it to the Service Layer.

In the service, I would like to use TestTemplate to interact with the Data API which use a URL, and How can I transform the PageRequest object to a query string like

page=1&size=20&sort=id,asc&sort=name,desc

then I can request data like:

restTemplate.getForEntity("http://data.mysite.com/products?page=1&size=20&sort=id,asc&sort=name,desc",String.class)