Cassandra UDF with Java throwing error on usage of stream - cassandra

Question

I am trying to write a UDF in Cassandra using Java.
I have two list of integers with one to one mapping i.e., first item in the first list corresponds to the first item in the second list. This is how my data is stored in Cassandra table under two columns of list type.
My UDF
CREATE OR REPLACE FUNCTION mykeyspace.get_thread(list1 List<int>, list2 List<int>)
CALLED ON NULL INPUT
RETURNS List<int>
LANGUAGE java
AS '
Map<Integer, Integer> intermediatemap = new HashMap<Integer, Integer>();
for (int i = 0; i < list1.size(); i++) {
if (!intermediatemap.containsKey(i))
intermediatemap.put(list1.get(i), list2.get(i));
}
List<Integer> commentids = new ArrayList<Integer>();
intermediatemap.entrySet().stream()
.sorted(Map.Entry.<Integer, Integer>comparingByValue().reversed())
.forEachOrdered(x -> commentids.add(x.getKey()));
if (commentids.size() > 8)
return commentids.subList(0, 8);
else
return commentids;
';
This is running all good as code. However, when I execute this on cqlsh I am getting error saying
InvalidRequest: Error from server: code=2200 [Invalid query] message="Java source compilation failed:
Line 8: The type java.util.stream.Stream cannot be resolved. It is indirectly referenced from required .class files
Line 8: The method stream() from the type Collection<Map.Entry<Integer,Integer>> refers to the missing type Stream
Is there any problem with the Cassandra version I am using? I am running the Cassandra on my local MAC machine inside a docker. I have tried with 3.11.2 and the image with latest tag.
Also, UDF function is enabled I am able to run simple UDF functions.

Answer 1

You can use only classes that are explicitly defined in the allowed classes list inside Cassandra, and not in the disallowed list defined. If you look to the source code for Cassandra 3.11.2, you can see that java.utils.stream is in the disallowed list, so you can't use it inside UDF/UDA.