Kafka从上手到实践-实践真知:Kafka Java Producer

这一节来看看如何使用Java编写Kafka Producer。

Create Kafka Project

创建Maven工程,在POM文件中加入如下两个依赖:

<dependency>
<groupId>org.apache.kafka</groupId>
<artifactId>kafka-clients</artifactId>
<version>2.0.0</version>
</dependency>

<dependency>
<groupId>org.slf4j</groupId>
<artifactId>slf4j-simple</artifactId>
<version>1.7.25</version>
</dependency>

第一个是Kafka的依赖包,用于创建Producer、ProducerRecord、Consumer等。第二个是Log4J的依赖包,用于输出日志。

Java Producer

首先创建Producer需要的配置信息,最基本的有三个信息:

  • Kafka集群的地址。
  • 发送的Message中Key的序列化方式。
  • 发送的Message中Value的序列化方式。
    Properties properties = new Properties();

    properties.setProperty(ProducerConfig.BOOTSTRAP_SERVERS_CONFIG, "IP:Port");

    properties.setProperty(ProducerConfig.KEY_SERIALIZER_CLASS_CONFIG, StringSerializer.class.getName());

    properties.setProperty(ProducerConfig.VALUE_SERIALIZER_CLASS_CONFIG, StringSerializer.class.getName());

然后传入上面实例化好的配置信息,实例化Producer:

KafkaProducer<String, String> kafkaProducer = new KafkaProducer<String, String>(properties);

然后实例化Record对象,该对象承载了要往哪个Topic发送以及Message内容的信息:

ProducerRecord<String, String> producerRecord = new ProducerRecord<String, String>("first_topic", "hello world!");

再然后发送Record:

kafkaProducer.send(producerRecord);

最后刷新和关闭Producer:

kafkaProducer.flush();
kafkaProducer.close();

以上就是最简单的Kafka Java Producer的编写方法。运行一下,可以看到类似如下的信息:

[main] INFO org.apache.kafka.common.utils.AppInfoParser - Kafka version : 2.0.0
[main] INFO org.apache.kafka.common.utils.AppInfoParser - Kafka commitId : 3402a8361b734732
[kafka-producer-network-thread | producer-1] INFO org.apache.kafka.clients.Metadata - Cluster ID: 4nh_0r5iQ_KsR_Fzf1HTGg
[main] INFO org.apache.kafka.clients.producer.KafkaProducer - [Producer clientId=producer-1] Closing the Kafka producer with timeoutMillis = 9223372036854775807 ms.

Process finished with exit code 0

Java Producer with Callback

如果我们希望在发送Message后,能监控发送状态,或者在发送异常时对异常进行处理。那么我们就可以使用带有Callback的发送方法:

kafkaProducer.send(producerRecord, new Callback() {
public void onCompletion(RecordMetadata recordMetadata, Exception e) {
if (e == null) {
logger.info("Received new metadata. \n" +
"Topic: " + recordMetadata.topic() + "\n" +
"Partition: " + recordMetadata.partition() + "\n" +
"Offset: " + recordMetadata.offset() + "\n" +
"Timestamp: " + recordMetadata.timestamp());
} else {
logger.error("Error while producing: ", e);
}
}
});

这样每次发送Message后,都会进入onCompletion这个方法中,然后可以使用RecordMetadata中记录的各种元数据做一些跟踪和监控的事情,同时如果发送异常了,也可以对异常进行处理。

[main] INFO org.apache.kafka.common.utils.AppInfoParser - Kafka version : 2.0.0
[main] INFO org.apache.kafka.common.utils.AppInfoParser - Kafka commitId : 3402a8361b734732
[kafka-producer-network-thread | producer-1] INFO org.apache.kafka.clients.Metadata - Cluster ID: 4nh_0r5iQ_KsR_Fzf1HTGg
[kafka-producer-network-thread | producer-1] INFO com.devtalking.jacefu.kafka.tutorial1.ProducerDemoWithCallback - Received new metadata. 
Topic: first_topic
Partition: 0
Offset: 22
Timestamp: 1546421392063
[main] INFO org.apache.kafka.clients.producer.KafkaProducer - [Producer clientId=producer-1] Closing the Kafka producer with timeoutMillis = 9223372036854775807 ms.

Process finished with exit code 0

Java Producer with Keys

在前文中,Partition的Compaction Cleanup Policy一节中介绍到,在压缩策略时,就涉及到了Message的Key和Value。我们来看看如何在发送Message时带着Key。

首先来看看ProducerRecord的另一个构造函数:

public ProducerRecord(String topic, K key, V value) {
this(topic, (Integer)null, (Long)null, key, value, (Iterable)null);
}

可以看到,刚才我们只使用了topicvalue两个参数,其中还有一个key,所以我们在实例化ProducerRecord时传入Key就可以了:

ProducerRecord<String, String> producerRecord = new ProducerRecord<String, String>("first_topic", "This is the key", "hello world!");

小结

之前三个章节介绍了如何使用Kafka CLI操作Kafka,其中包括Producer CLI和Consumer CLI。这一章节主要带大家实践如何使用Kafka提供的API编写Java Producer,希望可以给使用Java语言的小伙伴们带来帮助。

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