orderProcessWithSideEffect.java

@Bean
public Function<KStream<String, OrderInputMsg>, KStream<String, OrderInputMsg>> orderProcessWithSideEffect(){
    return stringOrderInputMsgKStream -> {
        KStream<String, String> stringStringKStream = stringOrderInputMsgKStream
                .mapValues((readOnlyKey, value) -> value.getOrderId());
        stringStringKStream.to("out-textMsg-topic-0", Produced.with(Serdes.String(), Serdes.String()));
        return stringOrderInputMsgKStream
                .mapValues((readOnlyKey, value) -> OrderProcessorService.processOrderMsg(value));
    };
}