Kafka Java Consumer 已经关闭

Question

我刚刚开始使用 Kafka。我正面临与消费者的一个小问题。我用Java编写了一个消费者。

我收到此异常 - IllegalStateException 此消费者已关闭。

以下行出现异常：

ConsumerRecords<String,String> consumerRecords = consumer.poll(1000);

在我的消费者因某些异常而崩溃之后开始发生这种情况，当我再次尝试运行它时，它给了我这个异常。

这是完整的代码：

package StreamApplicationsTest;

import org.apache.kafka.clients.consumer.*;
import org.apache.kafka.common.serialization.StringDeserializer;

import java.util.*;

public class StreamAppConsumer {

public static void main(String[] args){
    int i = 0;
    //List<String> topics = new ArrayList<>();
    List<String> topics = Collections.singletonList("test_topic");
    //topics.add("test_topic");
    Properties consumerConfigurations = new Properties();
    consumerConfigurations.put(ConsumerConfig.BOOTSTRAP_SERVERS_CONFIG,"localhost:9092");
    consumerConfigurations.put(ConsumerConfig.KEY_DESERIALIZER_CLASS_CONFIG, StringDeserializer.class.getName());
    consumerConfigurations.put(ConsumerConfig.VALUE_DESERIALIZER_CLASS_CONFIG,StringDeserializer.class.getName());
    consumerConfigurations.put(ConsumerConfig.GROUP_ID_CONFIG,"TestId");

    Consumer<String,String> consumer = new KafkaConsumer<>(consumerConfigurations);
    consumer.subscribe(topics);

    while(true){
        ConsumerRecords<String,String> consumerRecords = consumer.poll(1000);
        Iterator<ConsumerRecord<String,String>> iterator = consumerRecords.iterator();
        while(iterator.hasNext()){
            i++;
            ConsumerRecord<String,String> consumerRecord = iterator.next();
            String key = consumerRecord.key();
            String value = consumerRecord.value();
            if(key=="exit" || value=="exit")
                break;
            System.out.println("Key="+key+"\tValue="+value);
        }

        System.out.println("Messages processed = "+Integer.toString(i));
        consumer.close();

    }
}
}

我只是被这个问题所困扰，任何形式的帮助都会很有用。

Answer 1

发生这种情况是因为您在无限循环结束时关闭了消费者，因此当它第二次轮询消费者时，消费者已经关闭。为了解决眼前的问题，我将整个while(true) 循环包装在一个try-catch 中，并在catch 或finally 块中处理消费者关闭。

但是，如果 Kafka 使用者未仔细处理不同的关闭信号，您将面临丢失数据的风险。我建议查看 Confluent 的示例，以了解如何优雅地关闭消费者 here。在你的情况下，因为你在主线程中运行它看起来像这样......

public static void main(String[] args) {
    int i = 0;
    //List<String> topics = new ArrayList<>();
    List<String> topics = Collections.singletonList("test_topic");
    //topics.add("test_topic");
    Properties consumerConfigurations = new Properties();
    consumerConfigurations.put(ConsumerConfig.BOOTSTRAP_SERVERS_CONFIG, "localhost:9092");
    consumerConfigurations.put(ConsumerConfig.KEY_DESERIALIZER_CLASS_CONFIG, StringDeserializer.class.getName());
    consumerConfigurations.put(ConsumerConfig.VALUE_DESERIALIZER_CLASS_CONFIG, StringDeserializer.class.getName());
    consumerConfigurations.put(ConsumerConfig.GROUP_ID_CONFIG, "TestId");

    Consumer<String, String> consumer = new KafkaConsumer<>(consumerConfigurations);
    consumer.subscribe(topics);

    Runtime.getRuntime().addShutdownHook(new Thread()
    {
      public void run() {
        consumer.wakeup();
      }
    });

    try {
      while (true) {
        ConsumerRecords<String, String> consumerRecords = consumer.poll(1000);
        Iterator<ConsumerRecord<String, String>> iterator = consumerRecords.iterator();
        while (iterator.hasNext()) {
          i++;
          ConsumerRecord<String, String> consumerRecord = iterator.next();
          String key = consumerRecord.key();
          String value = consumerRecord.value();
          if (key == "exit" || value == "exit")
            break;
          System.out.println("Key=" + key + "\tValue=" + value);
        }
        System.out.println("Messages processed = " + Integer.toString(i));
      }
    } catch (WakeupExection e) {
      // Do Nothing
    } finally {
      consumer.close();
    }
  }
}

基本上运行consumer.wakeup() 是消费者中唯一的线程安全方法，因此它是唯一可以在Java 的关闭挂钩中运行的方法。由于调用唤醒时消费者没有睡着，它会触发唤醒执行，从而优雅地关闭消费者。

Answer 2

这似乎有效

public static void main(String[] args) {

        List<String> topics = new ArrayList<>();
        topics.add("test.topic");

        final Properties props = new Properties();
        props.put(ConsumerConfig.BOOTSTRAP_SERVERS_CONFIG, "IP_TO_KAFKA_SERVER");
        props.put(ConsumerConfig.GROUP_ID_CONFIG, "test");
        props.put(ConsumerConfig.VALUE_DESERIALIZER_CLASS_CONFIG, "org.apache.kafka.common.serialization.StringDeserializer");
        props.put(ConsumerConfig.KEY_DESERIALIZER_CLASS_CONFIG, "org.apache.kafka.common.serialization.StringDeserializer");

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

        System.out.println("Polling");
        ConsumerRecords<String, String> consumerRecords = consumer.poll(5000);

        try {
            for (ConsumerRecord<String, String> record : consumerRecords) {
                System.out.println(record.offset() + ": " + record.value());
            }
        } finally {
            consumer.close();
        }
    }

确保您的服务器或本地 kafka 可访问

输出

--- exec-maven-plugin:1.2.1:exec (default-cli) @ MVN ---
SLF4J: Failed to load class "org.slf4j.impl.StaticLoggerBinder".
SLF4J: Defaulting to no-operation (NOP) logger implementation
Polling
SLF4J: See http://www.slf4j.org/codes.html#StaticLoggerBinder for further details.
6: test
7: tes