Caroline Caroline - 3 months ago 15
Java Question

ServiceLoader to find implementations of an interface

I tried to use the Java ServiceLoader to find all classes that implement a specific interface like so:

loader = ServiceLoader.load(Operation.class);
try {
for (Operation o : loader) {
operations.add(o);
}
} catch (ServiceConfigurationError e) {
LOGGER.log(Level.SEVERE, "Uncaught exception", e);
}


Unfortunately, when I run Eclipse in debug mode the ServiceLoader doesn't find any classes. I feel like I'm missing a trivial point...

Answer

ServiceLoader cannot do it.

In order to expose class as a service that can be discovered by ServiceLoader you need to put its name into provider configuration file, as described in Creating Extensible Applications With the Java Platform .

There are no built-in ways find all classes that implement a particular interface. Frameworks that can do something similar use their own classpath scanning solutions (and even with custom classpath scanning it's not easy because .class files only store information about interfaces implemented directly, not transitively).