How to map input KStream <String,String> into <String, CarClass> using KeyValueMapper?

Question

Receiving the Json data which i simply want to map on CarClass and want to create new stream but map method doesn't allow me it to map on custom datatype The method map(KeyValueMapper>) in the type KStream is not applicable for the arguments (new KeyValueMapper>(){})?

Answer 1

From http://docs.confluent.io/current/streams/developer-guide.html#stateless-transformations:

The example changes the value type from byte[] to Integer. For String to CarClass is would be the same.

KStream<byte[], String> stream = ...;

// Java 8+ example, using lambda expressions
// Note how we change the key and the key type (similar to `selectKey`)
// as well as the value and the value type.
KStream<String, Integer> transformed = stream.map(
  (key, value) -> KeyValue.pair(value.toLowerCase(), value.length()));

// Java 7 example
KStream<String, Integer> transformed = stream.map(
  new KeyValueMapper<byte[], String, KeyValue<String, Integer>>() {
    @Override
    public KeyValue<String, Integer> apply(byte[] key, String value) {
      return new KeyValue<>(value.toLowerCase(), value.length());
    }
  });

However, if you want to only modify the value, I would recommend to use mapValues() instead of map().