CODEWITHSUNDEEP
spring-cloud-stream
JSBach
JSBach

Reputation: 4747

How to configure my processor so it can publish either 1 or 0 messages?

Let's imagine I have a processor that should filter out messages that are not important. How can I do that using Spring cloud streams?

I tried this example, but I get a null point exception:

    @Bean
    Function<String, String> upper() {
        return s -> s.length() < 5 ? null : s;
    }

I could change my processor to return a List<Messages<String>> or similar, but this would mean that my processor could produce 0, 1 or N messages, and I want it to be able to produce only 0 or 1.

Is there a way to do it?

Upvotes: 0

Views: 62

Answers (1)

Oleg Zhurakousky
Oleg Zhurakousky

Reputation: 6126

For this case you can use Consumer. The analogy of a glass half-full or half-empty. Basically you want to "occasionally" send output message. So you can do this:

@Bean
Consumer<String> upper(StreamBridge streamBridge) {
        return v -> {
           if (v.length() > 5) {
              streamBridge.send("destination_name", v);
           }
        };
}

NOTE: The "destination_name" is the name of your destination. If it doesn't exist it will be auto-provisioned on the first send. The second argument is the data you are sending. Could be Message could be POJO. . . up to you .

For more information on StreamBridge - https://docs.spring.io/spring-cloud-stream/docs/3.1.3/reference/html/spring-cloud-stream.html#_sending_arbitrary_data_to_an_output_e_g_foreign_event_driven_sources.

Now, returning 'null' as in your case should actually work, so please raise and issue - https://github.com/spring-cloud/spring-cloud-stream/issues

Upvotes: 1

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