Mastering Apache Storm

Custom grouping

If none of the preceding groupings fit your use case, you can define your own custom grouping by implementing the backtype.storm.grouping.CustomStreamGrouping interface.

Here is a sample custom grouping that partitions the stream on the basis of the category in the tuples:

public class CategoryGrouping implements CustomStreamGrouping, Serializable { private static final Map<String, Integer> categories = ImmutableMap.of ( "Financial", 0, "Medical", 1, "FMCG", 2, "Electronics", 3 ); private int tasks = 0; public void prepare(WorkerTopologyContext context, GlobalStreamId stream, List<Integer> targetTasks) { tasks = targetTasks.size(); } public List<Integer> chooseTasks(int taskId, List<Object> values) { String category = (String) ...