Spring Integration - 2 MessageHandlers handle half of messages - spring-integration

Question

I am using spring integration framework, with a Transformer
inputChannel -> kafka consumer
outputChannel -> database jdbc writer
#Bean
public DirectChannel inboundChannel() {
return new DirectChannel();
}
#Bean
public DirectChannel outboundChannel() {
return new DirectChannel();
}
#Bean
#Transformer(inputChannel="inboundChannel", outputChannel="outboundChannel")
public JsonToObjectTransformer jsonToObjectTransformer() {
return new JsonToObjectTransformer(Item.class);
}
#Bean
#ServiceActivator(inputChannel = "outboundChannel")
public MessageHandler jdbcmessageHandler() {
JdbcMessageHandler jdbcMessageHandler = new ...
return ...;
}
#Bean
#ServiceActivator(inputChannel = "inboundChannel")
public MessageHandler kafkahandler() {
return new ...;
}
in both handlers I override
public void handleMessage(Message<?> message)
The problem: if in kafka there are total N messages,
then each handleMessage() is invoked exactly n/2 times!
I assumed that each handler will be invoked n times, because each handler linked to different channel and there are n messages in total.
What am I missing?
(if I disable the kafak handler, the second handler gets all n messages)
Update:
I need to subscriber to get all the messages from the same channel (kafka handler will do something with the raw data, and jdbc handler will push the transformed
data)

Answer 1

First of all your inboundChannel and outboundChannel are out of use: you nowhere (at least in the question) specify their names.
The names like input and output are taken by the framework and used to create new MessageChannel beans, which are used in other places.
Now see what you have:
#Transformer(inputChannel="input"
#ServiceActivator(inputChannel = "input")
Both of them are subscribers to the same input channel and since it is created automatically by the framework as a DirectChannel. This channel is based on a round-robin LoadBalancingStrategy, therefore you see n/2 in your Kafka since its service activator deals only with every second message sent to that input channel.
Please, see more info in docs: https://docs.spring.io/spring-integration/reference/html/core.html#channel-configuration-directchannel