问题描述:

Im publishing to the remote kafka server and try to consume messages from that remote server. (Kafka v 0.90.1)

Publishing works fine but nor the consuming.

Publisher

package org.test;

import java.io.IOException;

import java.util.Properties;

import org.apache.kafka.clients.producer.KafkaProducer;

import org.apache.kafka.clients.producer.ProducerRecord;

public class Producer {

private void generateMessgaes() throws IOException {

String topic = "MY_TOPIC";

Properties props = new Properties();

props.put("bootstrap.servers", "kafka.xx.com:9092");

props.put("acks", "all");

props.put("retries", 0);

props.put("batch.size", 16384);

props.put("linger.ms", 1);

props.put("buffer.memory", 33554432);

props.put("key.serializer", "org.apache.kafka.common.serialization.StringSerializer");

props.put("value.serializer", "org.apache.kafka.common.serialization.StringSerializer");

props.put("serializer.class", "org.apache.kafka.common.serialization.StringSerializer");

KafkaProducer<String, String> producer = null;

try {

producer = new KafkaProducer<>(props);

for (int i = 0; i < 10; i++) {

producer.send(new ProducerRecord<String, String>(topic, "test msg"));

System.out.println("producing---");

}

} catch (Throwable e) {

e.printStackTrace();

System.out.println("Error in publishing messages to the topic : " + topic);

} finally {

producer.close();

}

}

public static void main(String[] args) throws IOException {

Producer producer = new Producer();

producer.generateMessgaes();

System.out.println("$$$$$");

}

}

I can see "producing--- and $$$$ prints. But when i try to consume, i do not see "polling " print messages.. It got stuck at poll(timeout).

Any clue?

Consumer

package org.test;

import java.util.Arrays;

import java.util.List;

import java.util.Properties;

import org.apache.kafka.clients.consumer.ConsumerRecord;

import org.apache.kafka.clients.consumer.ConsumerRecords;

import org.apache.kafka.clients.consumer.KafkaConsumer;

public class Listener {

public void start() throws CoreException {

String topic = "MY_TOPIC";

List<String> topics = Arrays.asList(topic);

Properties props = new Properties();

props.put("bootstrap.servers", "kafka.xx.com:9092");

props.put("enable.auto.commit", true);

props.put("receive.buffer.bytes", 262144);

props.put("consumer.timeout.ms", 10000);

props.put("session.timeout.ms", 7000);

props.put("heartbeat.interval.ms", 1000);

props.put("auto.offset.reset", "earliest");

props.put("group.id", "test");

props.put("fetch.min.bytes", 1);

props.put("key.deserializer", "org.apache.kafka.common.serialization.StringDeserializer");

props.put("value.deserializer", "org.apache.kafka.common.serialization.StringDeserializer");

props.put("serializer.class", "org.apache.kafka.common.serialization.StringDeserializer");

KafkaConsumer<String, String> consumer = new KafkaConsumer<String, String>(props);

consumer.subscribe(topics);

try {

while (true) {

ConsumerRecords<String, String> records = consumer.poll(100);

System.out.println("polling msges : " + records.count());

for (ConsumerRecord<String, String> record : records) {

System.out.println("kafka record : " + record.value());

}

}

} catch (Throwable e) {

e.printStackTrace();

System.out.println("eror in polling");

} finally {

consumer.close();

}

}

public static void main(String args[]) throws CoreException {

Listener listener = new Listener();

listener.start();

}

}

网友答案:

Disclaimer: I don't know Kafka but I do know messaging.

First thing about topics: by default, subscriptions are not persistent, so if a producers sends messages to the topic and there's no one listening, the messages are dropped.

Second thing is the polling: you're polling for 100ms and then if there's nothing there an exception is thrown, dropping you out of the loop.

If there's no messages when the consumer starts - because, as I described, the producer's messages went to the bit bucket - and then the consumer failed because there was nothing to consume. So I would say everything is working as you should expect.

Two options: -add a much larger initial polling to give the consumer a chance to see a message (assuming you know the producer is going to produce in the time frame) -change your logic such that an exception causes you to stay in the while loop and continue to consume, and figure out a different way to stop the consumer.

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