E-commerce open-source solutions

[nick.rowlands]

I am developing an e-commerce website for the first time. The website
will act as intermediary between companies and their customers. For
each transaction I will charge the appropriate company a fee. The
website will take orders and payment on behalf of the companies. The
system must include a billing system to invoice the companies monthly.

I will be developing in Java and I am investigating the available
options. I guess there are open-source and commercial solutions
available. Please advise on what solutions there are available to me or
if I should develop the system from scratch.

Regards,
Nick.