DATAMONGO-583 - Using while (…) instead of for (…) for DBCursors to avoid memory leak.

Instead of iterating over the DBCursor using a for-loop we now use a while-loop to avoid the potential memory leak outlined in [0].

[0] https://jira.mongodb.org/browse/JAVA-664

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

@@ -1513,7 +1513,12 @@ public class MongoTemplate implements MongoOperations, ApplicationContextAware {
 			CursorPreparer preparer, DbObjectCallback<T> objectCallback, String collectionName) {
 
 		try {
-			DBCursor cursor = collectionCallback.doInCollection(getAndPrepareCollection(getDb(), collectionName));
+
+			DBCursor cursor = null;
+
+			try {
+
+				cursor = collectionCallback.doInCollection(getAndPrepareCollection(getDb(), collectionName));
 
 				if (preparer != null) {
 					cursor = preparer.prepare(cursor);
@@ -1521,11 +1526,19 @@ public class MongoTemplate implements MongoOperations, ApplicationContextAware {
 
 				List<T> result = new ArrayList<T>();
 
-			for (DBObject object : cursor) {
+				while (cursor.hasNext()) {
+					DBObject object = cursor.next();
 					result.add(objectCallback.doWith(object));
 				}
 
 				return result;
+
+			} finally {
+
+				if (cursor != null) {
+					cursor.close();
+				}
+			}
 		} catch (RuntimeException e) {
 			throw potentiallyConvertRuntimeException(e);
 		}
@@ -1535,15 +1548,27 @@ public class MongoTemplate implements MongoOperations, ApplicationContextAware {
 			DocumentCallbackHandler callbackHandler, String collectionName) {
 
 		try {
-			DBCursor cursor = collectionCallback.doInCollection(getAndPrepareCollection(getDb(), collectionName));
+
+			DBCursor cursor = null;
+
+			try {
+				cursor = collectionCallback.doInCollection(getAndPrepareCollection(getDb(), collectionName));
 
 				if (preparer != null) {
 					cursor = preparer.prepare(cursor);
 				}
 
-			for (DBObject dbobject : cursor) {
+				while (cursor.hasNext()) {
+					DBObject dbobject = cursor.next();
 					callbackHandler.processDocument(dbobject);
 				}
+
+			} finally {
+				if (cursor != null) {
+					cursor.close();
+				}
+			}
+
 		} catch (RuntimeException e) {
 			throw potentiallyConvertRuntimeException(e);
 		}