I've been working for almost 7 years. I have a tendency to not use widely spread frameworks such as Spring, Hibernate\JPA, JSF\Struts\GWT..etc
I like to explore and use new frameworks and I like to understand how they work and explore all possible solutions to a single problem. This taught me to understand the concepts and methodologies running under the hood. I'm not saying that I know everything but that's what I like to do: Use and explore new frameworks and find out if they offer something profoundly new.
Now this has put me into an issue, most employers require experience in widely spread frameworks. I haven't used any of these frameworks but I understand the concept behind them and I most probably have used a similar framework.
For instance, I don't know how to write a Spring application but I know about dependency injection and have used Tapestry IoC (A dependency injection module in a web framework). I don't know how to use Hibernate but I've used Datanucleus\JDO a lot.
Should this be a real problem ? Why do employers always ask for developers who must be specialized in a specific framework ? I understand that it's not easy to upgrade currently used frameworks, needles to mention using another one, but shouldn't an experienced developer be able to handle ANY framework just by reading it's well organised documentation ?