Kafka String Deserializer with Logstash

Hi everyone
I am getting a problem on pushing data from Kafka to Logstash and getting following problem.
first, my data type is JSON file, original data
{"key":"value"}
I configured Kafka filesystem source connect to read JSON data and use following converters
value.converter=org.apache.kafka.connect.storage.StringConverter
key.converter=org.apache.kafka.connect.storage.StringConverter

The message stored in Kafka
Struct{value={"key":"value"}}

Now on Logstash I want to decode the serialized data to original data and use json plugin to parse the data.

Could you please suggest me the best approach?

Thanks so much.

Hi, anyone can help?
Thanks