Complete Vavr collection detection on TypeInformation and CustomConversions.

Moved Vavr collection converters into a type in the utility package. Register the converters via CustomConversions.registerConvertersIn(…) to make sure that all the Spring Data object mapping converters automatically benefit from a ConversionService that is capable of translating between Java-native collections and Vavr ones.

Issue #2511.

src/main/java/org/springframework/data/util/TypeDiscoverer.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2011-2021 the original author or authors.
+ * Copyright 2011-2022 the original author or authors.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -23,16 +23,7 @@ import java.lang.reflect.ParameterizedType;
 import java.lang.reflect.Type;
 import java.lang.reflect.TypeVariable;
 import java.lang.reflect.WildcardType;
-import java.util.ArrayList;
-import java.util.Arrays;
-import java.util.Collection;
-import java.util.Collections;
-import java.util.HashMap;
-import java.util.HashSet;
-import java.util.List;
-import java.util.Map;
-import java.util.Optional;
-import java.util.Set;
+import java.util.*;
 import java.util.concurrent.ConcurrentHashMap;
 import java.util.stream.Collectors;
 
@@ -347,23 +338,10 @@ class TypeDiscoverer<S> implements TypeInformation<S> {
 
 		return rawType.isArray() //
 				|| Iterable.class.equals(rawType) //
-				|| Streamable.class.isAssignableFrom(rawType)
+				|| Streamable.class.isAssignableFrom(rawType) //
 				|| isCollection();
 	}
 
-	private boolean isCollection() {
-
-		Class<S> type = getType();
-
-		for (Class<?> collectionType : COLLECTION_TYPES) {
-			if (collectionType.isAssignableFrom(type)) {
-				return true;
-			}
-		}
-
-		return false;
-	}
-
 	@Nullable
 	public final TypeInformation<?> getComponentType() {
 		return componentType.orElse(null);
@@ -386,7 +364,7 @@ class TypeDiscoverer<S> implements TypeInformation<S> {
 			return getTypeArgument(Iterable.class, 0);
 		}
 
-		if(isNullableWrapper()) {
+		if (isNullableWrapper()) {
 			return getTypeArgument(rawType, 0);
 		}
 
@@ -541,6 +519,24 @@ class TypeDiscoverer<S> implements TypeInformation<S> {
 		return hashCode;
 	}
 
+	/**
+	 * Returns whether the current type is considered a collection.
+	 *
+	 * @return
+	 */
+	private boolean isCollection() {
+
+		var type = getType();
+
+		for (Class<?> collectionType : COLLECTION_TYPES) {
+			if (collectionType.isAssignableFrom(type)) {
+				return true;
+			}
+		}
+
+		return false;
+	}
+
 	/**
 	 * A synthetic {@link ParameterizedType}.
 	 *

src/main/java/org/springframework/data/util/VavrCollectionConverters.java

@@ -0,0 +1,181 @@
+/*
+ * Copyright 2022 the original author or authors.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      https://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package org.springframework.data.util;
+
+import io.vavr.collection.LinkedHashMap;
+import io.vavr.collection.LinkedHashSet;
+import io.vavr.collection.Traversable;
+
+import java.util.Arrays;
+import java.util.Collection;
+import java.util.Collections;
+import java.util.HashSet;
+import java.util.List;
+import java.util.Map;
+import java.util.Set;
+import java.util.stream.Collectors;
+
+import org.springframework.core.convert.TypeDescriptor;
+import org.springframework.core.convert.converter.ConditionalGenericConverter;
+import org.springframework.lang.NonNull;
+import org.springframework.lang.Nullable;
+import org.springframework.util.ClassUtils;
+
+/**
+ * Converter implementations to map from and to Vavr collections.
+ *
+ * @author Oliver Gierke
+ * @author Christoph Strobl
+ * @since 2.7
+ */
+public class VavrCollectionConverters {
+
+	private static final boolean VAVR_PRESENT = ClassUtils.isPresent("io.vavr.control.Option",
+			NullableWrapperConverters.class.getClassLoader());
+
+	public static Collection<Object> getConvertersToRegister() {
+
+		if (!VAVR_PRESENT) {
+			return Collections.emptyList();
+		}
+
+		return Arrays.asList(ToJavaConverter.INSTANCE, FromJavaConverter.INSTANCE);
+	}
+
+	public enum ToJavaConverter implements ConditionalGenericConverter {
+
+		INSTANCE;
+
+		private static final TypeDescriptor TRAVERSAL_TYPE = TypeDescriptor.valueOf(Traversable.class);
+		private static final Set<Class<?>> COLLECTIONS_AND_MAP = new HashSet<>(
+				Arrays.asList(Collection.class, List.class, Set.class, Map.class));
+
+		@NonNull
+		@Override
+		public Set<ConvertiblePair> getConvertibleTypes() {
+
+			return COLLECTIONS_AND_MAP.stream()
+					.map(it -> new ConvertiblePair(Traversable.class, it))
+					.collect(Collectors.toSet());
+		}
+
+		@Override
+		public boolean matches(TypeDescriptor sourceType, TypeDescriptor targetType) {
+
+			return sourceType.isAssignableTo(TRAVERSAL_TYPE)
+					&& COLLECTIONS_AND_MAP.contains(targetType.getType());
+		}
+
+		@Nullable
+		@Override
+		public Object convert(@Nullable Object source, TypeDescriptor sourceType, TypeDescriptor targetType) {
+
+			if (source == null) {
+				return null;
+			}
+
+			if (source instanceof io.vavr.collection.Seq) {
+				return ((io.vavr.collection.Seq<?>) source).asJava();
+			}
+
+			if (source instanceof io.vavr.collection.Map) {
+				return ((io.vavr.collection.Map<?, ?>) source).toJavaMap();
+			}
+
+			if (source instanceof io.vavr.collection.Set) {
+				return ((io.vavr.collection.Set<?>) source).toJavaSet();
+			}
+
+			throw new IllegalArgumentException("Unsupported Vavr collection " + source.getClass());
+		}
+	}
+
+	public enum FromJavaConverter implements ConditionalGenericConverter {
+
+		INSTANCE {
+
+			@NonNull
+			@Override
+			public java.util.Set<ConvertiblePair> getConvertibleTypes() {
+				return CONVERTIBLE_PAIRS;
+			}
+
+			@Override
+			public boolean matches(TypeDescriptor sourceType, TypeDescriptor targetType) {
+
+				// Prevent collections to be mapped to maps
+				if (sourceType.isCollection() && io.vavr.collection.Map.class.isAssignableFrom(targetType.getType())) {
+					return false;
+				}
+
+				// Prevent maps to be mapped to collections
+				if (sourceType.isMap() && !(io.vavr.collection.Map.class.isAssignableFrom(targetType.getType())
+						|| targetType.getType().equals(Traversable.class))) {
+					return false;
+				}
+
+				return true;
+			}
+
+			@Nullable
+			@Override
+			public Object convert(@Nullable Object source, TypeDescriptor sourceDescriptor, TypeDescriptor targetDescriptor) {
+
+				var targetType = targetDescriptor.getType();
+
+				if (io.vavr.collection.Seq.class.isAssignableFrom(targetType)) {
+					return io.vavr.collection.List.ofAll((Iterable<?>) source);
+				}
+
+				if (io.vavr.collection.Set.class.isAssignableFrom(targetType)) {
+					return LinkedHashSet.ofAll((Iterable<?>) source);
+				}
+
+				if (io.vavr.collection.Map.class.isAssignableFrom(targetType)) {
+					return LinkedHashMap.ofAll((Map<?, ?>) source);
+				}
+
+				// No dedicated type asked for, probably Traversable.
+				// Try to stay as close to the source value.
+
+				if (source instanceof List) {
+					return io.vavr.collection.List.ofAll((Iterable<?>) source);
+				}
+
+				if (source instanceof Set) {
+					return LinkedHashSet.ofAll((Iterable<?>) source);
+				}
+
+				if (source instanceof Map) {
+					return LinkedHashMap.ofAll((Map<?, ?>) source);
+				}
+
+				return source;
+			}
+		};
+
+		private static final Set<ConvertiblePair> CONVERTIBLE_PAIRS;
+
+		static {
+
+			Set<ConvertiblePair> pairs = new HashSet<>();
+			pairs.add(new ConvertiblePair(Collection.class, io.vavr.collection.Traversable.class));
+			pairs.add(new ConvertiblePair(Map.class, io.vavr.collection.Traversable.class));
+
+			CONVERTIBLE_PAIRS = Collections.unmodifiableSet(pairs);
+		}
+	}
+}