Add server interceptor blending

This commit implements the `@GprcService(blendWithGlobalInterceptors)`
feature. This allows global and per-service server interceptors to be
combined into a single list and then finally sorted (i.e. blended).

Signed-off-by: Chris Bono <chris.bono@gmail.com>

spring-grpc-core/src/main/java/org/springframework/grpc/server/service/ApplicationContextBeanLookupUtils.java

@@ -20,6 +20,9 @@ import java.util.LinkedHashMap;
 import java.util.List;
 
 import org.springframework.context.ApplicationContext;
+import org.springframework.core.OrderComparator;
+import org.springframework.core.Ordered;
+import org.springframework.core.annotation.AnnotationAwareOrderComparator;
 import org.springframework.core.annotation.Order;
 import org.springframework.util.Assert;
 
@@ -93,4 +96,33 @@ final class ApplicationContextBeanLookupUtils {
 		return applicationContext.getBeanProvider(beanType).orderedStream().filter(beanToNameMap::containsKey).toList();
 	}
 
+	/**
+	 * Sorts the supplied list in place using an {@link OrderComparator} that takes the
+	 * {@link Order @Order} annotation on bean factory methods in configuration classes
+	 * into account.
+	 * @param applicationContext the application context
+	 * @param beanType the type of beans in the list
+	 * @param beans the list of beans to sort
+	 */
+	static void sortBeansIncludingOrderAnnotation(ApplicationContext applicationContext, Class<?> beanType,
+			List<?> beans) {
+		var beanToNameMap = new LinkedHashMap<Object, String>();
+		applicationContext.getBeansOfType(beanType).forEach((name, bean) -> beanToNameMap.put(bean, name));
+		beans.sort(OrderComparator.INSTANCE.withSourceProvider(bean -> {
+			Integer priority = AnnotationAwareOrderComparator.INSTANCE.getPriority(bean);
+			if (priority != null) {
+				return (Ordered) () -> priority;
+			}
+			// Consult the bean factory method for annotations
+			String beanName = beanToNameMap.get(bean);
+			if (beanName != null) {
+				Order order = applicationContext.findAnnotationOnBean(beanName, Order.class);
+				if (order != null) {
+					return (Ordered) order::value;
+				}
+			}
+			return null;
+		}));
+	}
+
 }

spring-grpc-core/src/main/java/org/springframework/grpc/server/service/DefaultGrpcServiceConfigurer.java

@@ -76,7 +76,10 @@ public class DefaultGrpcServiceConfigurer implements GrpcServiceConfigurer, Init
 		Arrays.stream(serviceInfo.interceptorNames())
 			.forEachOrdered((interceptorBeanName) -> allInterceptors
 				.add(this.applicationContext.getBean(interceptorBeanName, ServerInterceptor.class)));
-		// TODO handle blend
+		if (serviceInfo.blendWithGlobalInterceptors()) {
+			ApplicationContextBeanLookupUtils.sortBeansIncludingOrderAnnotation(this.applicationContext,
+					ServerInterceptor.class, allInterceptors);
+		}
 		return ServerInterceptors.interceptForward(serviceDef, allInterceptors);
 	}
 

spring-grpc-core/src/test/java/org/springframework/grpc/server/service/DefaultGrpcServiceConfigurerTests.java

@@ -25,7 +25,6 @@ import java.util.function.Function;
 
 import org.assertj.core.api.Assertions;
 import org.assertj.core.api.InstanceOfAssertFactories;
-import org.junit.jupiter.api.Disabled;
 import org.junit.jupiter.api.Nested;
 import org.junit.jupiter.api.Test;
 import org.mockito.MockedStatic;
@@ -256,7 +255,6 @@ class DefaultGrpcServiceConfigurerTests {
 		}
 
 		@SuppressWarnings("unchecked")
-		@Disabled("Needs 'blend interceptors' to be implemented")
 		@Test
 		void whenBlendInterceptorsTrueThenGlobalInterceptorsBlended() {
 			GrpcServiceInfo serviceInfo = new GrpcServiceInfo(

spring-grpc-docs/src/main/antora/modules/ROOT/pages/server.adoc

@@ -128,6 +128,16 @@ BindableService myService() {
 }
 ----
 
+[[server-interceptor-blending]]
+[TIP]
+====
+When a service is configured with both global and per-service interceptors, the global interceptors are first applied in their sorted order followed by the per-service interceptors in their sorted order.
+
+However, by setting the `blendWithGlobalInterceptors` attribute on the `@GrpcService` annotation to `"true"` you can change this behavior so that the interceptors are all combined and then sorted according to their bean natural ordering (i.e. `@Order`).
+
+You can use this option if you want to add a per-service interceptor between global interceptors.
+====
+
 == Observability
 
 Spring gRPC provides an autoconfigured interceptor that can be used to provide observability to your gRPC services.