From 024f1ae8bd16004ccc2c4afde4f7c2ab7c221a9e Mon Sep 17 00:00:00 2001
From: Oliver Gierke <ogierke@pivotal.io>
Date: Mon, 26 Sep 2016 15:01:14 +0200
Subject: [PATCH] DATACMNS-921 - ResultProcessor now gracefully  falls back to
 approximate collections if necessary.

When handling collection results, we now create an approximate collection in case the creation of the exact same collection fails.
---
 .../repository/query/ResultProcessor.java     | 18 +++++++++++++++-
 .../query/ResultProcessorUnitTests.java       | 21 +++++++++++++++++++
 2 files changed, 38 insertions(+), 1 deletion(-)

diff --git a/src/main/java/org/springframework/data/repository/query/ResultProcessor.java b/src/main/java/org/springframework/data/repository/query/ResultProcessor.java
index e65eaf3ce..3cdbb2b4e 100644
--- a/src/main/java/org/springframework/data/repository/query/ResultProcessor.java
+++ b/src/main/java/org/springframework/data/repository/query/ResultProcessor.java
@@ -143,7 +143,7 @@ public class ResultProcessor {
 		if (source instanceof Collection && method.isCollectionQuery()) {
 
 			Collection<?> collection = (Collection<?>) source;
-			Collection<Object> target = CollectionFactory.createCollection(collection.getClass(), collection.size());
+			Collection<Object> target = createCollectionFor(collection);
 
 			for (Object columns : collection) {
 				target.add(type.isInstance(columns) ? columns : converter.convert(columns));
@@ -159,6 +159,22 @@ public class ResultProcessor {
 		return (T) converter.convert(source);
 	}
 
+	/**
+	 * Creates a new {@link Collection} for the given source. Will try to create an instance of the source collection's
+	 * type first falling back to creating an approximate collection if the former fails.
+	 * 
+	 * @param source must not be {@literal null}.
+	 * @return
+	 */
+	private static Collection<Object> createCollectionFor(Collection<?> source) {
+
+		try {
+			return CollectionFactory.createCollection(source.getClass(), source.size());
+		} catch (RuntimeException o_O) {
+			return CollectionFactory.createApproximateCollection(source, source.size());
+		}
+	}
+
 	@RequiredArgsConstructor(staticName = "of")
 	private static class ChainingConverter implements Converter<Object, Object> {
 
diff --git a/src/test/java/org/springframework/data/repository/query/ResultProcessorUnitTests.java b/src/test/java/org/springframework/data/repository/query/ResultProcessorUnitTests.java
index d832e9a5d..450172e87 100644
--- a/src/test/java/org/springframework/data/repository/query/ResultProcessorUnitTests.java
+++ b/src/test/java/org/springframework/data/repository/query/ResultProcessorUnitTests.java
@@ -245,6 +245,20 @@ public class ResultProcessorUnitTests {
 		assertThat(result, is(instanceOf(WrappingDto.class)));
 	}
 
+	/**
+	 * @see DATACMNS-921
+	 */
+	@Test
+	public void fallsBackToApproximateCollectionIfNecessary() throws Exception {
+
+		ResultProcessor processor = getProcessor("findAllProjection");
+
+		SpecialList<Sample> specialList = new SpecialList<Sample>(new Object());
+		specialList.add(new Sample("Dave", "Matthews"));
+
+		processor.processResult(specialList);
+	}
+
 	private static ResultProcessor getProcessor(String methodName, Class<?>... parameters) throws Exception {
 		return getQueryMethod(methodName, parameters).getResultProcessor();
 	}
@@ -311,4 +325,11 @@ public class ResultProcessorUnitTests {
 		@Value("#{target.firstname + ' ' + target.lastname}")
 		String getFullName();
 	}
+
+	static class SpecialList<E> extends ArrayList<E> {
+
+		private static final long serialVersionUID = -6539525376878522158L;
+
+		public SpecialList(Object dummy) {}
+	}
 }