我有使用Apache Kafka 2.11-0.10.1.0的Java 8应用程序。我需要使用seek功能来poll来自分区的旧消息。但是，我遇到No current assignment for partition的异常，每次我尝试seekByOffset时都会发生。这是我的课程，负责将主题seek设置为指定的时间戳：
import org.apache.kafka.clients.consumer.ConsumerRecords;
import org.apache.kafka.clients.consumer.KafkaConsumer;
import org.apache.kafka.clients.consumer.OffsetAndTimestamp;
import org.apache.kafka.common.PartitionInfo;
import org.apache.kafka.common.TopicPartition;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
import org.springframework.util.CollectionUtils;
import java.time.Instant;
import java.util.Collection;
import java.util.Collections;
import java.util.List;
import java.util.Map;
import java.util.function.Function;
import java.util.regex.Pattern;
import java.util.stream.Collectors;
/**
* The main purpose of this class is to move fetching point for each partition of the {@link KafkaConsumer}
* to some offset which is determined either by timestamp or by offset number.
*/
public class KafkaSeeker {
public static final long APP_STARTUP_TIME = Instant.now().toEpochMilli();
private final Logger LOGGER = LoggerFactory.getLogger(this.getClass());
private final KafkaConsumer<String, String> kafkaConsumer;
private ConsumerRecords<String, String> polledRecords;
public KafkaSeeker(KafkaConsumer<String, String> kafkaConsumer) {
this.kafkaConsumer = kafkaConsumer;
this.polledRecords = new ConsumerRecords<>(Collections.emptyMap());
}
/**
* For each assigned or subscribed topic {@link org.apache.kafka.clients.consumer.KafkaConsumer#seek(TopicPartition, long)}
* fetching pointer to the specified {@code timestamp}.
* If no messages were found in each partition for a topic,
* then {@link org.apache.kafka.clients.consumer.KafkaConsumer#seekToEnd(Collection)} will be called.
*
* Due to {@link KafkaConsumer#subscribe(Pattern)} and {@link KafkaConsumer#assign(Collection)} laziness
* method needs to execute dummy {@link KafkaConsumer#poll(long)} method. All {@link ConsumerRecords} which were
* polled from buffer are swallowed and produce warning logs.
*
* @param timestamp is used to find proper offset to seek to
* @param topics are used to seek only specific topics. If not specified or empty, all subscribed topics are used.
*/
public Map<TopicPartition, OffsetAndTimestamp> seek(long timestamp, Collection<String> topics) {
this.polledRecords = kafkaConsumer.poll(0);
Collection<TopicPartition> topicPartitions;
if (CollectionUtils.isEmpty(topics)) {
topicPartitions = kafkaConsumer.assignment();
} else {
topicPartitions = topics.stream()
.map(it -> {
List<Integer> partitions = kafkaConsumer.partitionsFor(it).stream()
.map(PartitionInfo::partition).collect(Collectors.toList());
return partitions.stream().map(partition -> new TopicPartition(it, partition));
})
.flatMap(it -> it)
.collect(Collectors.toList());
}
if (topicPartitions.isEmpty()) {
throw new IllegalStateException("Kafka consumer doesn't have any subscribed topics.");
}
Map<TopicPartition, Long> timestampsByTopicPartitions = topicPartitions.stream()
.collect(Collectors.toMap(Function.identity(), topicPartition -> timestamp));
Map<TopicPartition, Long> beginningOffsets = kafkaConsumer.beginningOffsets(topicPartitions);
Map<TopicPartition, OffsetAndTimestamp> offsets = kafkaConsumer.offsetsForTimes(timestampsByTopicPartitions);
for (Map.Entry<TopicPartition, OffsetAndTimestamp> entry : offsets.entrySet()) {
TopicPartition topicPartition = entry.getKey();
if (entry.getValue() != null) {
LOGGER.info("Kafka seek topic:partition [{}:{}] from [{} offset] to [{} offset].",
topicPartition.topic(),
topicPartition.partition(),
beginningOffsets.get(topicPartition),
entry.getValue());
kafkaConsumer.seek(topicPartition, entry.getValue().offset());
} else {
LOGGER.info("Kafka seek topic:partition [{}:{}] from [{} offset] to the end of partition.",
topicPartition.topic(),
topicPartition.partition());
kafkaConsumer.seekToEnd(Collections.singleton(topicPartition));
}
}
return offsets;
}
public ConsumerRecords<String, String> getPolledRecords() {
return polledRecords;
}
}
在调用该方法之前，我已经让消费者订阅了一个consumer.subscribe(singletonList(kafkaTopic));这样的主题。当我得到kafkaConsumer.assignment()时，它将返回分配的零个TopicPartition。但是，如果我指定主题并获取其分区，那么我将拥有有效的TopicPartition，尽管它们在seek调用中失败，并出现标题错误。我忘记了什么？
答案 0 :(得分：3)
可靠地查找和检查当前分配的正确方法是在订阅后等待onPartitionsAssigned()回调。在新创建（仍未连接）的使用者上，一次调用poll()并不能保证它将立即连接并分配分区。
作为一个基本示例，请参见下面的代码，该代码订阅主题，并在分配的回调中查找所需的位置。最后，您会注意到轮询循环只能从查找位置正确看到记录，而不能从先前的提交或重置偏移量看到记录。
public static final Map<TopicPartition, Long> offsets = Map.of(new TopicPartition("testtopic", 0), 5L);
public static void main(String args[]) {
Properties props = new Properties();
props.put(ConsumerConfig.BOOTSTRAP_SERVERS_CONFIG, "localhost:9092");
props.put(ConsumerConfig.GROUP_ID_CONFIG, "test");
props.put(ConsumerConfig.KEY_DESERIALIZER_CLASS_CONFIG, StringDeserializer.class.getName());
props.put(ConsumerConfig.VALUE_DESERIALIZER_CLASS_CONFIG, StringDeserializer.class.getName());
try (Consumer<String, String> consumer = new KafkaConsumer<>(props)) {
consumer.subscribe(Collections.singletonList("testtopic"), new ConsumerRebalanceListener() {
@Override
public void onPartitionsRevoked(Collection<TopicPartition> partitions) {}
@Override
public void onPartitionsAssigned(Collection<TopicPartition> partitions) {
System.out.println("Assigned " + partitions);
for (TopicPartition tp : partitions) {
OffsetAndMetadata oam = consumer.committed(tp);
if (oam != null) {
System.out.println("Current offset is " + oam.offset());
} else {
System.out.println("No committed offsets");
}
Long offset = offsets.get(tp);
if (offset != null) {
System.out.println("Seeking to " + offset);
consumer.seek(tp, offset);
}
}
}
});
for (int i = 0; i < 10; i++) {
System.out.println("Calling poll");
ConsumerRecords<String, String> records = consumer.poll(Duration.ofMillis(100L));
for (ConsumerRecord<String, String> r : records) {
System.out.println("record from " + r.topic() + "-" + r.partition() + " at offset " + r.offset());
}
}
}
}
答案 1 :(得分：2)
KafkaConsumer<String, byte[]> consumer = new KafkaConsumer<>(props);
// Get topic partitions
List<TopicPartition> partitions = consumer
.partitionsFor(topic)
.stream()
.map(partitionInfo ->
new TopicPartition(topic, partitionInfo.partition()))
.collect(Collectors.toList());
// Explicitly assign the partitions to our consumer
consumer.assign(partitions);
//seek, query offsets, or poll
请注意，这会禁用消费者组管理和重新平衡操作。尽可能使用@Mickael Maison 的方法。