Explicitly check for declared usage of c

gselzer · ctrueden · commit b44cc06a8960 · 2021-11-19T20:36:27.000-06:00
diff --git a/scijava/scijava-ops-serviceloader/README.md b/scijava/scijava-ops-serviceloader/README.md
@@ -1,5 +1,4 @@
-# SciJava Discovery: A library for the abstraction of service discovery mechanisms
-
-This module provides the `Discoverer` interface, an abstraction for service discovery.
+# SciJava Ops Service Loader: A [`ServiceLoader`](https://docs.oracle.com/en/java/javase/11/docs/api/java.base/java/util/ServiceLoader.html)
+This module provides an implementation of `Discoverer`
 
 WIP
diff --git a/scijava/scijava-ops-serviceloader/src/main/java/org/scijava/ops/serviceloader/ServiceLoaderDiscoverer.java b/scijava/scijava-ops-serviceloader/src/main/java/org/scijava/ops/serviceloader/ServiceLoaderDiscoverer.java
@@ -14,15 +14,14 @@ public class ServiceLoaderDiscoverer implements Discoverer {
 	@SuppressWarnings("unchecked")
 	@Override
 	public <T> List<Class<T>> implementingClasses(Class<T> c) {
-		// TODO: can we first check that THIS module uses c?
-		try {
-			ServiceLoader<T> loader = ServiceLoader.load(c);
-			return loader.stream().map(p -> (Class<T>) p.get().getClass()) //
-				.collect(Collectors.toList());
-		}
-		catch (ServiceConfigurationError e) {
-			return Collections.emptyList();
-		}
+		// If we cannot use c, we cannot find any implementations
+		Module thisModule = this.getClass().getModule();
+		if (!thisModule.canUse(c)) return Collections.emptyList();
+
+		// If we can use c, look up the implementations
+		ServiceLoader<T> loader = ServiceLoader.load(c);
+		return loader.stream().map(p -> (Class<T>) p.get().getClass()) //
+			.collect(Collectors.toList());
 	}
 
 }
