Default factory for stubs when scanning as documented

Also add failing test. Fixes #172.

samples/grpc-server/src/test/java/org/springframework/grpc/sample/GrpcClientApplicationTests.java

@@ -79,4 +79,29 @@ public class GrpcClientApplicationTests {
 
 	}
 
+	@Nested
+	@SpringBootTest
+	@AutoConfigureInProcessTransport
+	class ExplicitImportClientsWithNoFactory {
+
+		@Autowired
+		private ApplicationContext context;
+
+		@Test
+		void stubOfCorrectTypeIsCreated() {
+			assertThat(context.containsBeanDefinition("simpleBlockingStub")).isTrue();
+			assertThat(context.getBean(SimpleGrpc.SimpleBlockingStub.class)).isNotNull();
+			assertThat(context.containsBeanDefinition("simpleStub")).isFalse();
+			assertThat(context.containsBeanDefinition("simpleFutureStub")).isFalse();
+			assertThat(context.getBeanNamesForType(AbstractStub.class)).hasSize(1);
+		}
+
+		@TestConfiguration
+		@ImportGrpcClients
+		static class TestConfig {
+
+		}
+
+	}
+
 }

spring-grpc-core/src/main/java/org/springframework/grpc/client/GrpcClientFactory.java

@@ -184,6 +184,9 @@ public class GrpcClientFactory {
 	private static boolean supports(Class<?> factory, Class<?> type) {
 		// To avoid needing to instantiate the factory we use reflection to check for a
 		// static supports() method. If it exists we call it.
+		if (factory == null) {
+			return false;
+		}
 		Method method = ReflectionUtils.findMethod(factory, "supports", Class.class);
 		boolean supports = false;
 		if (method != null) {
@@ -260,17 +263,18 @@ public class GrpcClientFactory {
 			Set<Class<?>> allTypes = new HashSet<>();
 			allTypes.addAll(Set.of(this.types));
 			for (String basePackage : this.packages) {
+				Class<?> factoryToUse = this.factory == null ? BlockingStubFactory.class : this.factory;
 				TypeFilter filter = new TypeFilter() {
 					@Override
 					public boolean match(MetadataReader metadataReader, MetadataReaderFactory metadataReaderFactory)
 							throws IOException {
 						Class<?> type = ClassUtils.resolveClassName(metadataReader.getClassMetadata().getClassName(),
 								ClasspathScanner.class.getClassLoader());
-						return supports(GrpcClientRegistrationSpec.this.factory, type);
+						return supports(factoryToUse, type);
 					}
 				};
 				for (Class<?> type : SCANNER.scan(basePackage, filter)) {
-					if (findDefaultFactory(registry, this.factory, type) != null) {
+					if (findDefaultFactory(registry, factoryToUse, type) != null) {
 						allTypes.add(type);
 					}
 				}