How to implement N-input and N-output using KStream and spring.cloud.stream

Stream Processing Kafka Streams
1

I am trying to implement an N-input stream and N-output stream
Where I have multiple input topics and multiple output topics.
E.g.:
Input_topic_1 ----> Output_topic_1 and Output_topic_2
Input_topic_2 -----> Output_topic_2 and Output_topic_3
Input_topic_3 -----> Output_topic_1 and Output_topic_3
Single stream works with method signature:

@Bean
public Function<KStream<String, String>, KStream<String, JsonNode>[]> process()

Even BiFunction works for 2 inputs.

@Bean
public BiFunction<KStream<String, String>, KStream<String, String>, KStream<String, JsonNode>[]> process() {

But My use case is to process more than 2 inputs. In Java, there is Function And BiFunction to take input parameters, I have tried using

@Bean
public Function<KStream<String, String>[], KStream<String, JsonNode>[]> process()

And

@Bean
public Function<List<KStream<String, String>>, KStream<String, JsonNode>[]> process()

but App not able to recognize process method:

app.yaml:

spring:
  cloud:
    stream:
      kafka:
        streams:
          binder:
            configuration:
              commit.interval.ms: 1000
              default.key.serde: org.apache.kafka.common.serialization.Serdes$StringSerde
              default.value.serde: org.apache.kafka.common.serialization.Serdes$StringSerde
              num.stream.threads: 2 
            zkNodes: localhost:2181
            brokers: localhost:9092 

          default:
            consumer:
              applicationId: app1
      function:
        definition: process
        bindings:
           process-in-0:
            destination: in-1
           process-in-1:
             destination: in-2
           process-in-2:
             destination: in-3
           process-out-0:
             destination: out-1
           process-out-1:
             destination: out-2
           process-out-2:
             destination: out-3

I am sure, something is wrong with the method signature. Please help me to get the correct approach to achieve n-input and n-output. TIA!!

2

Using “plain” Kafka Streams, that is certainly possible… I am not familiar with Spring though, and don’t know how to do it there (or if possible with Spring).