Polishing.

Support DBObject and Map that as source for entity materialization and map conversion.

See #3702
Original pull request: #3704.

spring-data-mongodb/src/main/java/org/springframework/data/mongodb/core/convert/MappingMongoConverter.java

@@ -1909,14 +1909,11 @@ public <S extends Object> S convert(Object source, TypeInformation<? extends S>
 			if (typeHint.isMap()) {
 
 				if(ClassUtils.isAssignable(Document.class, typeHint.getType())) {
-					return (S) documentConverter.convert(this, (Bson) source, typeHint);
+					return (S) documentConverter.convert(this, BsonUtils.asBson(source), typeHint);
 				}
 
-				if(source instanceof Bson) {
-					return (S) mapConverter.convert(this, (Bson) source, typeHint);
-				}
-				if(source instanceof Map) {
-					return (S) mapConverter.convert(this, new Document((Map<String,Object>) source), typeHint);
+				if (BsonUtils.supportsBson(source)) {
+					return (S) mapConverter.convert(this, BsonUtils.asBson(source), typeHint);
 				}
 
 				throw new IllegalArgumentException(String.format("Expected map like structure but found %s", source.getClass()));
@@ -1931,8 +1928,8 @@ public <S extends Object> S convert(Object source, TypeInformation<? extends S>
 						String.format(INCOMPATIBLE_TYPES, source, BasicDBList.class, typeHint.getType(), getPath()));
 			}
 
-			if (source instanceof Bson) {
-				return (S) documentConverter.convert(this, (Bson) source, typeHint);
+			if (BsonUtils.supportsBson(source)) {
+				return (S) documentConverter.convert(this, BsonUtils.asBson(source), typeHint);
 			}
 
 			return (S) elementConverter.convert(source, typeHint);

spring-data-mongodb/src/main/java/org/springframework/data/mongodb/util/BsonUtils.java

@@ -488,6 +488,49 @@ private static Map<String, Object> getAsMap(Object source) {
 		return null;
 	}
 
+	/**
+	 * Returns the given source object as {@link Bson}, i.e. {@link Document}s and maps as is or throw
+	 * {@link IllegalArgumentException}.
+	 *
+	 * @param source
+	 * @return the converted/casted source object.
+	 * @throws IllegalArgumentException if {@code source} cannot be converted/cast to {@link Bson}.
+	 * @since 3.2.3
+	 * @see #supportsBson(Object)
+	 */
+	@SuppressWarnings("unchecked")
+	public static Bson asBson(Object source) {
+
+		if (source instanceof Document) {
+			return (Document) source;
+		}
+
+		if (source instanceof BasicDBObject) {
+			return (BasicDBObject) source;
+		}
+
+		if (source instanceof DBObject) {
+			return new Document(((DBObject) source).toMap());
+		}
+
+		if (source instanceof Map) {
+			return new Document((Map<String, Object>) source);
+		}
+
+		throw new IllegalArgumentException(String.format("Cannot convert %s to Bson", source));
+	}
+
+	/**
+	 * Returns the given source can be used/converted as {@link Bson}.
+	 *
+	 * @param source
+	 * @return {@literal true} if the given source can be converted to {@link Bson}.
+	 * @since 3.2.3
+	 */
+	public static boolean supportsBson(Object source) {
+		return source instanceof DBObject || source instanceof Map;
+	}
+
 	/**
 	 * Returns given object as {@link Collection}. Will return the {@link Collection} as is if the source is a
 	 * {@link Collection} already, will convert an array into a {@link Collection} or simply create a single element

spring-data-mongodb/src/test/java/org/springframework/data/mongodb/core/convert/MappingMongoConverterUnitTests.java

@@ -934,10 +934,11 @@ void convertsSetToBasicDBList() {
 		assertThat(readResult.iterator().next()).isInstanceOf(Address.class);
 	}
 
-	@Test // DATAMONGO-402
+	@Test // DATAMONGO-402, GH-3702
 	void readsMemberClassCorrectly() {
 
-		org.bson.Document document = new org.bson.Document("inner", new org.bson.Document("value", "FOO!"));
+		org.bson.Document document = new org.bson.Document("inner",
+				new LinkedHashMap<>(new org.bson.Document("value", "FOO!")));
 
 		Outer outer = converter.read(Outer.class, document);
 		assertThat(outer.inner).isNotNull();

spring-data-mongodb/src/test/java/org/springframework/data/mongodb/util/json/BsonUtilsTest.java

@@ -19,7 +19,7 @@
 
 import java.util.ArrayList;
 import java.util.Collection;
-import java.util.List;
+import java.util.Collections;
 
 import org.bson.BsonDouble;
 import org.bson.BsonInt32;
@@ -29,10 +29,16 @@
 import org.bson.Document;
 import org.bson.types.ObjectId;
 import org.junit.jupiter.api.Test;
+
 import org.springframework.data.mongodb.util.BsonUtils;
 
+import com.mongodb.BasicDBList;
+
 /**
+ * Unit tests for {@link BsonUtils}.
+ *
  * @author Christoph Strobl
+ * @author Mark Paluch
  */
 class BsonUtilsTest {
 
@@ -111,4 +117,13 @@ void asCollectionConvertsWrapsNonIterable() {
 
 		assertThat((Collection)BsonUtils.asCollection(source)).containsExactly(source);
 	}
+
+	@Test // GH-3702
+	void supportsBsonShouldReportIfConversionSupported() {
+
+		assertThat(BsonUtils.supportsBson("foo")).isFalse();
+		assertThat(BsonUtils.supportsBson(new Document())).isTrue();
+		assertThat(BsonUtils.supportsBson(new BasicDBList())).isTrue();
+		assertThat(BsonUtils.supportsBson(Collections.emptyMap())).isTrue();
+	}
 }