Processor node in kafka streams - apache-kafka

Question

I am working on processor node in kafka streams. For a simple code, I have written like below just to filter UserID , is this the correct way of doing processor node in kafka streams ?
But, the below code doesn't compile, throws an error with : The method filter(Predicate<? super Object,? super Object>) in the type KStream<Object,Object> is not applicable for the arguments (new Predicate<String,String>(){})
KStreamBuilder builder = new KStreamBuilder();
builder.stream(topic)
.filter(new Predicate <String, String>() {
//#Override
public boolean test(String key, String value) {
Hashtable<Object, Object> message;
// put you processor logic here
return message.get("UserID").equals("1");
}
})
.to(streamouttopic);
final KafkaStreams streams = new KafkaStreams(builder, props);
final CountDownLatch latch = new CountDownLatch(1);
// attach shutdown handler to catch control-c
Runtime.getRuntime().addShutdownHook(new Thread("streams-shutdown-hook") {
#Override
public void run() {
streams.close();
latch.countDown();
}
});
try {
streams.start();
latch.await();
} catch (Throwable e) {
System.exit(1);
}
System.exit(0);
Can someone guide me please?

Answer 1

builder.stream(topic) returns KStream<Object,Object> type because you don't specify the generic types. And <Object,Object> is not compatible with <String,String>.
If you know, that the actual type is KStream<String,String> you can specify the type as follows:
builder.<Sting,String>stream(topic)
.filter(...)
To answer you question about "processor nodes": yes, adding a filter() will add a processor node internally. Note, that at DSL level, you don't need to think in term of processors usually.
If you want to use processors explicitly, you can use Processor API instead of the DSL. Check out the WordCount example: https://github.com/apache/kafka/blob/trunk/streams/examples/src/main/java/org/apache/kafka/streams/examples/wordcount/WordCountProcessorDemo.java
Note, that using the DSL, internally the code will be translated into a processor topology which is the runtime model of Kafka Streams.

Answer 2

Probably you are using Predicate class from another package. You need to use
import org.apache.kafka.streams.kstream.Predicate;