#1335 - Support for Supplier<Stream<?> expansion in EmbeddedWrappers.

This allows types like Spring Data's Streamable to be piped into the ….wrap(…) methods and immediately resolved into a collection.

src/main/java/org/springframework/hateoas/server/core/EmbeddedWrappers.java

@@ -19,10 +19,12 @@ import java.util.Arrays;
 import java.util.Collection;
 import java.util.Collections;
 import java.util.Optional;
+import java.util.function.Supplier;
 import java.util.stream.Collectors;
 import java.util.stream.Stream;
 
 import org.springframework.aop.support.AopUtils;
+import org.springframework.core.ResolvableType;
 import org.springframework.hateoas.EntityModel;
 import org.springframework.hateoas.LinkRelation;
 import org.springframework.lang.NonNull;
@@ -36,6 +38,8 @@ import org.springframework.util.Assert;
  */
 public class EmbeddedWrappers {
 
+	private static ResolvableType SUPPLIER_OF_STREAM = ResolvableType.forClassWithGenerics(Supplier.class, Stream.class);
+
 	private final boolean preferCollections;
 
 	/**
@@ -83,9 +87,12 @@ public class EmbeddedWrappers {
 			return (EmbeddedWrapper) source;
 		}
 
-		return source instanceof Collection || source instanceof Stream || preferCollections
-				? new EmbeddedCollection(asCollection(source), rel)
-				: new EmbeddedElement(source, rel);
+		return source instanceof Collection //
+				|| source instanceof Stream //
+				|| preferCollections //
+				|| SUPPLIER_OF_STREAM.isAssignableFrom(source.getClass()) //
+						? new EmbeddedCollection(asCollection(source), rel) //
+						: new EmbeddedElement(source, rel);
 	}
 
 	@SuppressWarnings("unchecked")
@@ -107,6 +114,10 @@ public class EmbeddedWrappers {
 			return Arrays.asList((Object[]) source);
 		}
 
+		if (SUPPLIER_OF_STREAM.isInstance(source)) {
+			return asCollection(((Supplier<Stream<?>>) source).get());
+		}
+
 		return Collections.singleton(source);
 	}
 

src/test/java/org/springframework/hateoas/server/core/EmbeddedWrappersUnitTest.java

@@ -17,8 +17,12 @@ package org.springframework.hateoas.server.core;
 
 import static org.assertj.core.api.Assertions.*;
 
+import lombok.RequiredArgsConstructor;
+
 import java.util.Collection;
 import java.util.Collections;
+import java.util.function.Supplier;
+import java.util.stream.Stream;
 
 import org.junit.jupiter.api.Test;
 import org.springframework.hateoas.LinkRelation;
@@ -69,10 +73,36 @@ class EmbeddedWrappersUnitTest {
 		});
 	}
 
+	@Test // #1335
+	@SuppressWarnings("unchecked")
+	void addsSupplierOfStreamByResolvingIt() {
+
+		EmbeddedWrapper wrap = wrappers.wrap(new Streamable<>(Stream.of(1, 2, 3)));
+
+		assertThat(wrap.getValue()).isInstanceOfSatisfying(Collection.class, it -> {
+			assertThat(it).containsExactly(1, 2, 3);
+		});
+	}
+
 	@SuppressWarnings("unchecked")
 	private static void assertEmptyCollectionValue(EmbeddedWrapper wrapper) {
 
 		assertThat(wrapper.getValue()) //
 				.isInstanceOfSatisfying(Collection.class, it -> assertThat(it).isEmpty());
 	}
+
+	@RequiredArgsConstructor
+	static class Streamable<T> implements Supplier<Stream<T>> {
+
+		private final Stream<T> stream;
+
+		/*
+		 * (non-Javadoc)
+		 * @see java.util.function.Supplier#get()
+		 */
+		@Override
+		public Stream<T> get() {
+			return stream;
+		}
+	}
 }