Flink keyed stream key is null

Question

I am trying to perform a map operation on a KeyedStream in Flink:

stream.map(new JsonToMessageObjectMapper())
                    .keyBy(\"keyfield\")
                   


        

Answer 1

The problem is that you try to access the keyed state in the open() method.

Keyed state maintains a state instance for each key. In your example you are using MapState. So you have one MapState instance for each key. When accessing the state, you'll always get the state instance that corresponds to the key of the currently processed record. In a MapFunction (like in your example) this would be the record that is passed to the map() method.

Since open() is not called with a record, the current key in open() is null and it is not possible to access the keyed state.