DATACMNS-489 - Support for Future<T> as return value wrapper for repository methods.

Added a converter to process a NullableWrapper into a Future by producing an AsyncResult. This is to support repository methods annotated with @Async and returning a Future<T>. With Spring's asynchronous method invocation support activated this will cause the repository method being executed asynchronously.

Note, that this currently only works on Spring 4 as Spring 3.2.8 async support is not discovering the introduction on the repository proxy and thus fails to discover the @Async annotation on the repository method. This will be resolved in Spring 3.2.9, see the related tickets.

Related tickets: DATACMNS-483, SPR-11725, DATACMNS-499.

src/main/java/org/springframework/data/repository/util/QueryExecutionConverters.java

@@ -18,9 +18,11 @@ package org.springframework.data.repository.util;
 import java.util.Collections;
 import java.util.HashSet;
 import java.util.Set;
+import java.util.concurrent.Future;
 
 import org.springframework.core.convert.converter.Converter;
 import org.springframework.core.convert.support.ConfigurableConversionService;
+import org.springframework.scheduling.annotation.AsyncResult;
 import org.springframework.util.Assert;
 import org.springframework.util.ClassUtils;
 
@@ -48,6 +50,9 @@ public class QueryExecutionConverters {
 		Set<Class<?>> wrapperTypes = new HashSet<Class<?>>();
 		Set<Converter<?, ?>> converters = new HashSet<Converter<?, ?>>();
 
+		wrapperTypes.add(Future.class);
+		converters.add(ObjectToFutureConverter.INSTANCE);
+
 		if (GUAVA_PRESENT) {
 			wrapperTypes.add(ObjectToGuavaOptionalConverter.INSTANCE.getWrapperType());
 			converters.add(ObjectToGuavaOptionalConverter.INSTANCE);
@@ -133,4 +138,23 @@ public class QueryExecutionConverters {
 			return java.util.Optional.class;
 		}
 	}
+
+	/**
+	 * A Spring {@link Converter} to support returning {@link Future} instances from repository methods.
+	 * 
+	 * @author Oliver Gierke
+	 */
+	private static enum ObjectToFutureConverter implements Converter<NullableWrapper, Future<Object>> {
+
+		INSTANCE;
+
+		/* 
+		 * (non-Javadoc)
+		 * @see org.springframework.core.convert.converter.Converter#convert(java.lang.Object)
+		 */
+		@Override
+		public Future<Object> convert(NullableWrapper source) {
+			return new AsyncResult<Object>(source.getValue());
+		}
+	}
 }