Initialize lists with size where possible.

Closes #3941
Original pull request: #3974.

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

@@ -176,16 +176,20 @@ class CountQuery {
 		Document $geoWithinMin = new Document("$geoWithin",
 				new Document(spheric ? "$centerSphere" : "$center", $centerMin));
 
-		List<Document> criteria = new ArrayList<>();
+		List<Document> criteria;
 
 		if ($and != null) {
 			if ($and instanceof Collection) {
-				criteria.addAll((Collection) $and);
+				Collection andElements = (Collection) $and;
+				criteria = new ArrayList<>(andElements.size() + 2);
+				criteria.addAll(andElements);
 			} else {
 				throw new IllegalArgumentException(
 						"Cannot rewrite query as it contains an '$and' element that is not a Collection: Offending element: "
 								+ $and);
 			}
+		} else {
+			criteria = new ArrayList<>(2);
 		}
 
 		criteria.add(new Document("$nor", Collections.singletonList(new Document(key, $geoWithinMin))));

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

@@ -172,7 +172,8 @@ public class DefaultIndexOperations implements IndexOperations {
 
 			private List<IndexInfo> getIndexData(MongoCursor<Document> cursor) {
 
-				List<IndexInfo> indexInfoList = new ArrayList<>();
+				int available = cursor.available();
+				List<IndexInfo> indexInfoList = available > 0 ? new ArrayList<>(available) : new ArrayList<>();
 
 				while (cursor.hasNext()) {
 

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

@@ -945,7 +945,7 @@ public class MongoTemplate implements MongoOperations, ApplicationContextAware,
 		DocumentCallback<GeoResult<T>> callback = new GeoNearResultDocumentCallback<>(distanceField,
 				new ProjectingReadCallback<>(mongoConverter, projection, collection), near.getMetric());
 
-		List<GeoResult<T>> result = new ArrayList<>();
+		List<GeoResult<T>> result = new ArrayList<>(results.getMappedResults().size());
 
 		BigDecimal aggregate = BigDecimal.ZERO;
 		for (Document element : results) {
@@ -1311,7 +1311,7 @@ public class MongoTemplate implements MongoOperations, ApplicationContextAware,
 
 		Assert.notNull(writer, "MongoWriter must not be null");
 
-		List<Document> documentList = new ArrayList<>();
+		List<Document> documentList = new ArrayList<>(batchToSave.size());
 		List<T> initializedBatchToSave = new ArrayList<>(batchToSave.size());
 		for (T uninitialized : batchToSave) {
 
@@ -2717,7 +2717,8 @@ public class MongoTemplate implements MongoOperations, ApplicationContextAware,
 					.initiateFind(getAndPrepareCollection(doGetDatabase(), collectionName), collectionCallback::doInCollection)
 					.iterator()) {
 
-				List<T> result = new ArrayList<>();
+				int available = cursor.available();
+				List<T> result = available > 0 ? new ArrayList<>(available) : new ArrayList<>();
 
 				while (cursor.hasNext()) {
 					Document object = cursor.next();

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

@@ -1474,7 +1474,7 @@ public class ReactiveMongoTemplate implements ReactiveMongoOperations, Applicati
 			LOGGER.debug(String.format("Inserting list of Documents containing %d items", dbDocList.size()));
 		}
 
-		List<Document> documents = new ArrayList<>();
+		List<Document> documents = new ArrayList<>(dbDocList.size());
 
 		return execute(collectionName, collection -> {
 

spring-data-mongodb/src/main/java/org/springframework/data/mongodb/core/aggregation/ConditionalOperators.java

@@ -649,10 +649,7 @@ public class ConditionalOperators {
 			if (value instanceof CriteriaDefinition) {
 
 				Document mappedObject = context.getMappedObject(((CriteriaDefinition) value).getCriteriaObject());
-				List<Object> clauses = new ArrayList<Object>();
+				List<Object> clauses = getClauses(context, mappedObject);
-
-				clauses.addAll(getClauses(context, mappedObject));
-
 				return clauses.size() == 1 ? clauses.get(0) : clauses;
 			}
 
@@ -679,7 +676,9 @@ public class ConditionalOperators {
 
 			if (predicate instanceof List) {
 
-				List<Object> args = new ArrayList<Object>();
+				List<?> predicates = (List<?>) predicate;
+				List<Object> args = new ArrayList<Object>(predicates.size());
+
 				for (Object clause : (List<?>) predicate) {
 					if (clause instanceof Document) {
 						args.addAll(getClauses(context, (Document) clause));
@@ -697,14 +696,14 @@ public class ConditionalOperators {
 						continue;
 					}
 
-					List<Object> args = new ArrayList<Object>();
+					List<Object> args = new ArrayList<Object>(2);
 					args.add("$" + key);
 					args.add(nested.get(s));
 					clauses.add(new Document(s, args));
 				}
 			} else if (!isKeyword(key)) {
 
-				List<Object> args = new ArrayList<Object>();
+				List<Object> args = new ArrayList<Object>(2);
 				args.add("$" + key);
 				args.add(predicate);
 				clauses.add(new Document("$eq", args));

spring-data-mongodb/src/main/java/org/springframework/data/mongodb/core/aggregation/ExposedFields.java

@@ -110,7 +110,7 @@ public final class ExposedFields implements Iterable<ExposedField> {
 	private static ExposedFields createFields(Fields fields, boolean synthetic) {
 
 		Assert.notNull(fields, "Fields must not be null");
-		List<ExposedField> result = new ArrayList<ExposedField>();
+		List<ExposedField> result = new ArrayList<ExposedField>(fields.size());
 
 		for (Field field : fields) {
 			result.add(new ExposedField(field, synthetic));

spring-data-mongodb/src/main/java/org/springframework/data/mongodb/core/aggregation/Fields.java

@@ -167,6 +167,10 @@ public final class Fields implements Iterable<Field> {
 		return result;
 	}
 
+	public int size() {
+		return fields.size();
+	}
+
 	@Nullable
 	public Field getField(String name) {
 

spring-data-mongodb/src/main/java/org/springframework/data/mongodb/core/aggregation/GeoNearOperation.java

@@ -114,7 +114,7 @@ public class GeoNearOperation implements AggregationOperation {
 		Document command = toDocument(context);
 		Number limit = (Number) command.get("$geoNear", Document.class).remove("num");
 
-		List<Document> stages = new ArrayList<>();
+		List<Document> stages = new ArrayList<>(3);
 		stages.add(command);
 
 		if (nearQuery.getSkip() != null && nearQuery.getSkip() > 0) {

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

@@ -126,7 +126,7 @@ public class DefaultDbRefResolver extends DefaultReferenceResolver implements Db
 
 		List<Document> result = mongoCollection //
 				.find(new Document(BasicMongoPersistentProperty.ID_FIELD_NAME, new Document("$in", ids))) //
-				.into(new ArrayList<>());
+				.into(new ArrayList<>(ids.size()));
 
 		return ids.stream() //
 				.flatMap(id -> documentWithId(id, result)) //

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

@@ -418,7 +418,7 @@ abstract class GeoConverters {
 				return null;
 			}
 
-			List<Object> argument = new ArrayList<>();
+			List<Object> argument = new ArrayList<>(2);
 
 			Shape shape = source.getShape();
 
@@ -438,7 +438,9 @@ abstract class GeoConverters {
 
 			} else if (shape instanceof Polygon) {
 
-				for (Point point : ((Polygon) shape).getPoints()) {
+				List<Point> points = ((Polygon) shape).getPoints();
+				argument = new ArrayList(points.size());
+				for (Point point : points) {
 					argument.add(toList(point));
 				}
 

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

@@ -1000,14 +1000,14 @@ public class MappingMongoConverter extends AbstractMongoConverter implements App
 							.getPointer();
 				}).collect(Collectors.toList());
 
-				return writeCollectionInternal(targetCollection, TypeInformation.of(DocumentPointer.class), new ArrayList<>());
+				return writeCollectionInternal(targetCollection, TypeInformation.of(DocumentPointer.class), new ArrayList<>(targetCollection.size()));
 			}
 
 			if (property.hasExplicitWriteTarget()) {
-				return writeCollectionInternal(collection, new FieldTypeInformation<>(property), new ArrayList<>());
+				return writeCollectionInternal(collection, new FieldTypeInformation<>(property), new ArrayList<>(collection.size()));
 			}
 
-			return writeCollectionInternal(collection, property.getTypeInformation(), new ArrayList<>());
+			return writeCollectionInternal(collection, property.getTypeInformation(), new ArrayList<>(collection.size()));
 		}
 
 		List<Object> dbList = new ArrayList<>(collection.size());
@@ -1092,7 +1092,9 @@ public class MappingMongoConverter extends AbstractMongoConverter implements App
 				collection.add(getPotentiallyConvertedSimpleWrite(element,
 						componentType != null ? componentType.getType() : Object.class));
 			} else if (element instanceof Collection || elementType.isArray()) {
-				collection.add(writeCollectionInternal(BsonUtils.asCollection(element), componentType, new ArrayList<>()));
+
+				Collection<?> objects = BsonUtils.asCollection(element);
+				collection.add(writeCollectionInternal(objects, componentType, new ArrayList<>(objects.size())));
 			} else {
 				Document document = new Document();
 				writeInternal(element, document, componentType);

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

@@ -373,7 +373,7 @@ public class QueryMapper {
 		if (keyword.isOrOrNor() || (keyword.hasIterableValue() && !keyword.isGeometry())) {
 
 			Iterable<?> conditions = keyword.getValue();
-			List<Object> newConditions = new ArrayList<>();
+			List<Object> newConditions = conditions instanceof Collection ? new ArrayList<>(((Collection<?>) conditions).size()) : new ArrayList<>();
 
 			for (Object condition : conditions) {
 				newConditions.add(isDocument(condition) ? getMappedObject((Document) condition, entity)

spring-data-mongodb/src/main/java/org/springframework/data/mongodb/core/query/Criteria.java

@@ -337,7 +337,7 @@ public class Criteria implements CriteriaDefinition {
 	 * @see <a href="https://docs.mongodb.com/manual/reference/operator/query/mod/">MongoDB Query operator: $mod</a>
 	 */
 	public Criteria mod(Number value, Number remainder) {
-		List<Object> l = new ArrayList<Object>();
+		List<Object> l = new ArrayList<Object>(2);
 		l.add(value);
 		l.add(remainder);
 		criteria.put("$mod", l);

spring-data-mongodb/src/main/java/org/springframework/data/mongodb/repository/query/ConvertingParameterAccessor.java

@@ -165,8 +165,10 @@ public class ConvertingParameterAccessor implements MongoParameterAccessor {
 			if (property.isAssociation()) {
 				if (next.getClass().isArray() || next instanceof Iterable) {
 
-					List<DBRef> dbRefs = new ArrayList<DBRef>();
+					Collection<?> values = asCollection(next);
-					for (Object element : asCollection(next)) {
+
+					List<DBRef> dbRefs = new ArrayList<DBRef>(values.size());
+					for (Object element : values) {
 						dbRefs.add(writer.toDBRef(element, property));
 					}
 
@@ -196,11 +198,14 @@ public class ConvertingParameterAccessor implements MongoParameterAccessor {
 
 		if (source instanceof Iterable) {
 
-			List<Object> result = new ArrayList<Object>();
+			if(source instanceof Collection) {
+				return new ArrayList<>((Collection<?>) source);
+			}
+
+			List<Object> result = new ArrayList<>();
 			for (Object element : (Iterable<?>) source) {
 				result.add(element);
 			}
-
 			return result;
 		}