本篇博主带来的是Kafka的Consumer API操作。
Consumer消费数据时的可靠性是很容易保证的，因为数据在Kafka中是持久化的，故不用担心数据丢失问题。
由于consumer在消费过程中可能会出现断电宕机等故障，consumer恢复后，需要从故障前的位置的继续消费，所以consumer需要实时记录自己消费到了哪个offset，以便故障恢复后继续消费。
所以offset的维护是Consumer消费数据是必须考虑的问题。
1. 手动提交offset
- 1. 导入依赖
<build> <plugins> <plugin> <groupId>org.apache.maven.plugins</groupId> <artifactId>maven-compiler-plugin</artifactId> <configuration> <source>8</source> <target>8</target> </configuration> </plugin> </plugins> </build> <dependencies> <dependency> <groupId>org.apache.kafka</groupId> <artifactId>kafka-clients</artifactId> <version>0.11.0.2</version> </dependency> </dependencies>
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- 2. 编写代码
需要用到的类：
KafkaConsumer：需要创建一个消费者对象，用来消费数据
ConsumerConfig：获取所需的一系列配置参数
ConsuemrRecord：每条数据都要封装成一个ConsumerRecord对象
package com.buwenbuhuo.kafka.consumer;
import org.apache.kafka.clients.consumer.ConsumerConfig;
import org.apache.kafka.clients.consumer.ConsumerRecord;
import org.apache.kafka.clients.consumer.ConsumerRecords;
import org.apache.kafka.clients.consumer.KafkaConsumer;
import org.apache.kafka.common.serialization.StringDeserializer;
import java.util.Arrays;
import java.util.Properties;
/**
* @author 卜温不火
* @create 2020-05-06 23:22
* com.buwenbuhuo.kafka.consumer - the name of the target package where the new class or interface will be created.
* kafka0506 - the name of the current project.
*/
public class CustomConsumer { public static void main(String[] args) { Properties props = new Properties(); props.put(ConsumerConfig.BOOTSTRAP_SERVERS_CONFIG, "hadoop002:9092"); props.put(ConsumerConfig.KEY_DESERIALIZER_CLASS_CONFIG, StringDeserializer.class.getName()); props.put(ConsumerConfig.VALUE_DESERIALIZER_CLASS_CONFIG, StringDeserializer.class.getName()); props.put(ConsumerConfig.AUTO_OFFSET_RESET_CONFIG, "earliest"); props.put(ConsumerConfig.GROUP_ID_CONFIG, "bigData-0507"); props.put(ConsumerConfig.ENABLE_AUTO_COMMIT_CONFIG,true); props.put(ConsumerConfig.AUTO_COMMIT_INTERVAL_MS_CONFIG,3000); //1.创建1个消费者 KafkaConsumer<String, String> consumer = new KafkaConsumer<>(props); consumer.subscribe(Arrays.asList("first")); //2.调用poll try { while (true) { ConsumerRecords<String, String> records = consumer.poll(100); for (ConsumerRecord<String, String> record : records) { System.out.println("record = " + record); } } }finally { consumer.close(); } }
}
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- 3. 结果呈现
- 4. 代码分析
手动提交offset的方法有两种：分别是commitSync（同步提交）和commitAsync（异步提交）。两者的相同点是，都会将本次poll的一批数据最高的偏移量提交；不同点是，commitSync会失败重试，一直到提交成功（如果由于不可恢复原因导致，也会提交失败）；而commitAsync则没有失败重试机制，故有可能提交失败。
- 5. 此为异步提交代码
package com.buwenbuhuo.kafka.consumer;
import org.apache.kafka.clients.consumer.ConsumerConfig;
import org.apache.kafka.clients.consumer.ConsumerRecord;
import org.apache.kafka.clients.consumer.ConsumerRecords;
import org.apache.kafka.clients.consumer.KafkaConsumer;
import org.apache.kafka.common.serialization.StringDeserializer;
import java.util.Arrays;
import java.util.Properties;
/**
* @author 卜温不火
* @create 2020-05-06 23:22
* com.buwenbuhuo.kafka.consumer - the name of the target package where the new class or interface will be created.
* kafka0506 - the name of the current project.
*/
public class CustomConsumer { public static void main(String[] args) { Properties props = new Properties(); props.put(ConsumerConfig.BOOTSTRAP_SERVERS_CONFIG, "hadoop002:9092"); props.put(ConsumerConfig.KEY_DESERIALIZER_CLASS_CONFIG, StringDeserializer.class.getName()); props.put(ConsumerConfig.VALUE_DESERIALIZER_CLASS_CONFIG, StringDeserializer.class.getName()); props.put(ConsumerConfig.AUTO_OFFSET_RESET_CONFIG, "earliest"); props.put(ConsumerConfig.GROUP_ID_CONFIG, "bigData-0507"); props.put(ConsumerConfig.ENABLE_AUTO_COMMIT_CONFIG,false); //1.创建1个消费者 KafkaConsumer<String, String> consumer = new KafkaConsumer<>(props); consumer.subscribe(Arrays.asList("second")); //2.调用poll try { while (true) { ConsumerRecords<String, String> records = consumer.poll(100); for (ConsumerRecord<String, String> record : records) { System.out.println("record = " + record); } // 异步提交 consumer.commitAsync(); } }finally { consumer.close(); } }
}
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- 6. 此为同步提交代码
package com.buwenbuhuo.kafka.consumer;
import org.apache.kafka.clients.consumer.ConsumerConfig;
import org.apache.kafka.clients.consumer.ConsumerRecord;
import org.apache.kafka.clients.consumer.ConsumerRecords;
import org.apache.kafka.clients.consumer.KafkaConsumer;
import org.apache.kafka.common.serialization.StringDeserializer;
import java.util.Arrays;
import java.util.Properties;
/**
* @author 卜温不火
* @create 2020-05-06 23:22
* com.buwenbuhuo.kafka.consumer - the name of the target package where the new class or interface will be created.
* kafka0506 - the name of the current project.
*/
public class CustomConsumer { public static void main(String[] args) { Properties props = new Properties(); props.put(ConsumerConfig.BOOTSTRAP_SERVERS_CONFIG, "hadoop002:9092"); props.put(ConsumerConfig.KEY_DESERIALIZER_CLASS_CONFIG, StringDeserializer.class.getName()); props.put(ConsumerConfig.VALUE_DESERIALIZER_CLASS_CONFIG, StringDeserializer.class.getName()); props.put(ConsumerConfig.AUTO_OFFSET_RESET_CONFIG, "earliest"); props.put(ConsumerConfig.GROUP_ID_CONFIG, "bigData-0507"); props.put(ConsumerConfig.ENABLE_AUTO_COMMIT_CONFIG,false); //1.创建1个消费者 KafkaConsumer<String, String> consumer = new KafkaConsumer<>(props); consumer.subscribe(Arrays.asList("second")); //2.调用poll try { while (true) { ConsumerRecords<String, String> records = consumer.poll(100); for (ConsumerRecord<String, String> record : records) { System.out.println("record = " + record); } // 同步提交 consumer.commitSync(); } }finally { consumer.close(); } }
}
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- 7. 结果图
2. 自动提交offset
为了使我们能够专注于自己的业务逻辑，Kafka提供了自动提交offset的功能。
自动提交offset的相关参数：
enable.auto.commit：是否开启自动提交offset功能
auto.commit.interval.ms：自动提交offset的时间间隔
- 1. 代码
package com.buwenbuhuo.kafka.consumer;
import org.apache.kafka.clients.consumer.ConsumerConfig;
import org.apache.kafka.clients.consumer.ConsumerRecord;
import org.apache.kafka.clients.consumer.ConsumerRecords;
import org.apache.kafka.clients.consumer.KafkaConsumer;
import org.apache.kafka.common.serialization.StringDeserializer;
import java.util.Arrays;
import java.util.Properties;
/**
* @author 卜温不火
* @create 2020-05-06 23:22
* com.buwenbuhuo.kafka.consumer - the name of the target package where the new class or interface will be created.
* kafka0506 - the name of the current project.
*/
public class CustomConsumer { public static void main(String[] args) { Properties props = new Properties(); props.put("bootstrap.servers", "hadoop002:9092"); props.put("group.id", "test"); props.put("enable.auto.commit", "true"); props.put("auto.commit.interval.ms", "1000"); props.put("key.deserializer", "org.apache.kafka.common.serialization.StringDeserializer"); props.put("value.deserializer", "org.apache.kafka.common.serialization.StringDeserializer"); KafkaConsumer<String, String> consumer = new KafkaConsumer<>(props); consumer.subscribe(Arrays.asList("second")); while (true) { ConsumerRecords<String, String> records = consumer.poll(100); for (ConsumerRecord<String, String> record : records) System.out.printf("offset = %d, key = %s, value = %s%n", record.offset(), record.key(), record.value()); } }
}
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- 2. 运行结果
3. 自己维护offset
- 1. 代码
package com.buwenbuhuo.kafka.consumer;
import org.apache.kafka.clients.consumer.ConsumerRebalanceListener;
import org.apache.kafka.clients.consumer.ConsumerRecord;
import org.apache.kafka.clients.consumer.ConsumerRecords;
import org.apache.kafka.clients.consumer.KafkaConsumer;
import org.apache.kafka.common.TopicPartition;
import java.util.Arrays;
import java.util.Collection;
import java.util.Properties;
/**
* @author 卜温不火
* @create 2020-05-07 15:16
* com.buwenbuhuo.kafka.consumer - the name of the target package where the new class or interface will be created.
* kafka0506 - the name of the current project.
*/
public class CustomOffsetConsumer { public static void main(String[] args) { Properties props = new Properties(); props.put("bootstrap.servers", "hadoop002:9092"); props.put("group.id", "test");//消费者组，只要group.id相同，就属于同一个消费者组 props.put("enable.auto.commit", "false");//自动提交offset props.put("key.deserializer", "org.apache.kafka.common.serialization.StringDeserializer"); props.put("value.deserializer", "org.apache.kafka.common.serialization.StringDeserializer"); KafkaConsumer<String, String> consumer = new KafkaConsumer<>(props); consumer.subscribe(Arrays.asList("second"), new ConsumerRebalanceListener() { //提交当前负责的分区的offset @Override public void onPartitionsRevoked(Collection<TopicPartition> partitions) { System.out.println("==========回收的分区==========="); for (TopicPartition partition : partitions){ System.out.println("partition = " + partition); // 啥也没干不写东西也可以 } } //定位新分配的分区的offset @Override public void onPartitionsAssigned(Collection<TopicPartition> partitions) { System.out.println("========重新得到的分区==========="); for (TopicPartition partition : partitions) { Long offset = getPartitionOffset(partition); consumer.seek(partition,offset); } } }); while (true) { ConsumerRecords<String, String> records = consumer.poll(100); for (ConsumerRecord<String, String> record : records) { System.out.printf("offset = %d, key = %s, value = %s%n", record.offset(), record.key(), record.value()); TopicPartition topicPartition = new TopicPartition(record.topic(), record.partition()); commitOffset(topicPartition,record.offset()+1); } } } private static void commitOffset(TopicPartition topicPartition, long l) { } private static Long getPartitionOffset(TopicPartition partition) { return null; }
}
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- 2. 结果
本次的分享就到这里了,
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文章来源: buwenbuhuo.blog.csdn.net，作者：不温卜火，版权归原作者所有，如需转载，请联系作者。
原文链接：buwenbuhuo.blog.csdn.net/article/details/105962083