If you've ever tried to use SPI, you're familiar with the hassle of maintaining the meta files necessary for the system to work. Especially early on when a system is under heavy flux, keeping everything in sync can be a frustrating, error-fraught experience. Many just plow through it. Others turn to automated solutions and here is where the trouble begins.
If you're smart you look for a library and if you're lucky you find one that fits your needs. For one reason or another, some choose to write their own library. I know I've written one. Kohsuke of hudson fame has written one. If i were to use one today, I'd probably end up using this one. I don't see it on the home page, but I seem to remember Reinier Zwitserloot suggesting that lombok had one in the works. There are probably a dozen more out if one cared to dig deep enough (I don't). But it shouldn't be this way.
So we have a situation where using a built-in feature to the java runtime is so awkward that we have all these competing, divergent solutions. It's time for the JDK team to provide a native apt plugin to handle this natively. Any feature that drives so many to build work arounds for it clearly is missing something. In my opinion, this should be done by the JDK team and included in Java 8 at the latest. If it takes filing a JSR to get it into Java 8, great. I'd even lead it if necessary. Build an amalgam of the solutions out. Bundle an existing implement. Build one from scratch. Anything. But please, give us something native so we can stop inventing the wheel over and over again.
To take it even a step further, I'd push for building a type database by default when building a jar. Fantom has very nice way to tell the system, "Give me everything of type X." This kind of "database" would be trivial to build during either the compilation or jar bundling phase. But to be able to ask the JVM, give me references to all the classes implementing the interface FooBar would be an amazingly useful facility to have. It would eliminate the need for jar/classpath scanning at start up for everything from simple plugin systems to full blown EE stacks.
So what do you think? Is it too late for something like this in Java 8? Or Java 7 update mumblemuble? It'd be an amazing addition.