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POHow is the Java Service Provide API supposed to work?
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  1. POHow is the Java Service Provide API supposed to work?
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    copied!<p>It seems like everybody has had an unpleasant brush with the <a href="http://download.oracle.com/javase/1.4.2/docs/guide/jar/jar.html#Service%20Provider" rel="noreferrer">Java Service Provider</a>, that thing you can do with a file named like META-INF/services/com.example.Interface, but that nobody uses except for trying to load the right XML parser. I'm trying to work with a library that uses the Service Provider API, and trick it so that I can provide some runtime-extended classes (using cglib) that don't actually implement the interface but can be made to do so easily.</p> <p>Basically, I think the steps I need to perform are:<ol> <li>Create a custom class loader that will respond to getResources(...) and return an "extra" URL</li> <li>Also have that class loader hook getResourceAsStream(...) to return a list of the classes I am going to manipulate with cglib, when asked for the "extra" resource</li> <li>Finally, have that class loader load those classes when requested</li></ol></p> <p>But here's where I get lost. For example, when the library tries to determine what implementers are out there, it calls getResources(...) which returns a bunch of URLs. But getResourceAsStream(...) doesn't take URLs, it takes "names". Names which seem to be classpath-relative, and therefore the same everywhere. So META-INF/services/com.example.Interface in has the same "name" as META-INF/services/com.example.Interface in their JAR, right? Except somehow this works with those blasted XML parsers...</p> <p>Of course, all of this assumes they were smart/kind enough to call ClassLoader.getSystemClassLoader() rather than using ClassLoader.getSystemResources(...), ClassLoader.getSystemResourceAsStream(...), etc., as in the latter case there's no way to hook the ClassLoader and provide the faked file.</p> <p>I guess in that case I could use BCEL to manipulate the class files when my code is being packaged by Maven, rather than waiting until runtime to do it with cglib?</p>
 

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