Today is the first day of PayPal’s much-hyped PayPal Innovate X 2009, the payments company’s first dedicated developer conference. PayPal, which reported strong earnings recently, is hoping to engage developers in producing applications on top of PayPal’s newly released API. We reported on parts of the open platform here and here. PayPal is already testing the platform with startups Payvment, FundRazr, Lottay and TwitPay. PayPal is officially opening up its platform to developers and also unveiling additional APIs at the conference and will be presenting a roadmap for its view of the future of payments.

And PayPal is even gaining traction from large tech companies to integrate the new API. This morning, Sun Microsystems announced a partnership with PayPal to support for-fee applications submitted by developers for distribution in the Java Store. Utilizing the new Adaptive Payment API from PayPal, consumers can authorize the Java Store to bill against their PayPal account so they can simply click the “Buy” button and never have to leave the store. In addition,