It's this "de facto" nature of the Spring Framework that Google appears to have been drawn to. Although the open source nature of Spring likely played a role since key parts of GAE/J are based on open source projects, as Forrester analyst Jeffrey Hammond writes:
VMWare gives Google a significant boost in enterprise developer permission. While Google is the darling of developers outside the firewall, they still struggle inside the firewall. The reality is that enterprise IT development shops are just different than Web startups or Web giants. And enterprise Java development is something that the Spring folks understand. While I question the magnitude of the adoption percentages that SpringSource general manager Rod Johnson quoted yesterday, our own research with Dr. Dobbs and Eclipse developers confirms that Spring is indeed one of the most popular frameworks among Java developers at large shops (with a fair amount of Apache Struts and homegrown frameworks as alternatives).
But will the "de facto" nature of Spring be enough to get enterprises past the sparsely supported standards on GAE/J? On one hand, Spring's "de facto" nature adds to GAE/J's issues. Like GAE/J, Spring is not compliant with Java standards. Yet you can clearly argue that a lack of open standards compliance hasn't affected Spring's adoption.
Still, as I wrote in response to SpringSource CEO Rod Johnson, VMware's involvement may change the equation in the minds of IT decision makers:
Enterprises didn't much care about lock-in to the nonstandard Spring portfolio when it was from SpringSource, a small, friendly, company. Now that it's coming from VMware, a large enterprise software vendor with well-established profit motivations, it would be wise to get behind a relevant Java spec, like Java EE 6 Web Profile.
Over the past nine months, and as recently as a WebSphere conference two weeks ago, I've heard of large enterprises using Spring that are planning on migrating to open standards. For them, being open source is no longer enough to alleviate fears of lock-in now that VMware is part of the equation.
I am in no way suggesting Spring usage in the enterprise is going to decline by half overnight or anything ludicrous like that. However, enterprises are starting to consider their future freedom of action with applications locked into a framework controlled solely by one of the largest software vendors on the planet.