How can I retrieve int array rather than list of Integers in Java Mongo API?

Question

I have a Mongo Document that contains a large list of primitive ints. Using the Java MongoDB API, I can store the int[] directly, for example:

DBCollection coll = test.getCollection("test");
int[] myInts = {3,4,5,56};
DBObject doc = new BasicDBObject("arr", myInts);
coll.insert(doc);

But when I retrieve the data, I get back a BasicDBList that contains Integer objects:

DBCollection coll = test.getCollection("test");
DBObject obj = coll.findOne();
BasicDBList list =(BasicDBList)obj.get("arr");

Is there a way of getting this data in the same form that I inserted it (int[])? Because the arrays are going to be very large, I don't want an Integer object created for every array element.

I realize that from a coding point of view, there's no problem. The problem is that I am dealing with large amounts of data, and I don't want the memory and processing overhead of creating Integer objects, when my application only requires ints. — Ellen
– Ellen, Commented Oct 17, 2013 at 21:56

Rob Moore · Accepted Answer · 2013-10-18 02:34:49Z

0

Generally - no. You are going to get a List back.

You can try saving the array as a binary blob but then you will lose the ability to query that array and you will have to encode/decode the bytes to/from the array of integers.

There is some overhead in transforming the integer value into Integer objects but that overhead is limited by the JVM maintaining a cache of the Integer values from -128 to 127. (You have some control with the -XX:AutoBoxCacheMax for oracle JVMs). The (array) list itself will have minimal overhead compared to an array of int.

answered Oct 18, 2013 at 2:34

Rob Moore

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2 Comments

Ellen Over a year ago

Thank you, that's interesting - I think my worry was because I've had trouble when dealing with large arrays of Doubles, and I thought the same would be true of Integers.

Ellen Over a year ago

Just wanted to check - the range you specified is for bytes. I'm wondering if the caching works for larger ranges too (shorts and ints). I will check out that JVM option.

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