kafka pruducer api介绍

刺骨的言语ヽ痛彻心扉 2021-08-29 12:35 339阅读 0赞

对于kafka client建议使用java版本的api（kafka0.9版本中客户端代码使用java重构了一次），通过下面配置添加：（下面配置只会添加java版本的jar）

<dependency> 
      <groupId>org.apache.kafka</groupId> 
      <artifactId>kafka-clients</artifactId> 
      <version>0.10.0.1</version> 
    </dependency>

1）Kafka包括以下四种核心API：

*  The [Producer API][] allows an application to publish a stream of records to one or more Kafka topics.
 *  The [Consumer API][] allows an application to subscribe to one or more topics and process the stream of records produced to them.
 *  The [Streams API][] allows an application to act as a stream processor, consuming an input stream from one or more topics and producing an output stream to one or more output topics, effectively transforming the input streams to output streams.
 *  The [Connector API][] allows building and running reusable producers or consumers that connect Kafka topics to existing applications or data systems. For example, a connector to a relational database might capture every change to a table.

这里我们来讲解比较基础的Producer和Consumer。

2）说明：

kafka client有新旧两个版本，在kafka0.9中全部使用了新版本的客户端api（使用java重构过）。旧版本的客户端api是使用scala实现的。新旧客户端api对比：

//旧版本
    kafka.javaapi.producer.Producer<K,V>
    
    //新版本
    org.apache.kafka.clients.producer.KafkaProducer<K,V>

## 1、新版producer api ： ##

Producer用来向Kafka集群中发布消息记录的Kafka客户端。Producer是线程安全的，并且通常来讲，在多个线程间共享一个producer要比每个线程都创建一个producer速度更快。

producer由一个缓冲池（buffer pool）和一个I / O后台线程组成，新版producer api采用异步批量方式发送消息。该缓冲池保存尚未传输到服务器的消息记录，I / O线程负责将这些记录转换为请求并将它们传输到broker集群，使用后需要关闭生产者资源，关闭时会自动检查缓冲区的消息，将剩余消息发送到broker。

1.1）producer 消息发送方式：

1）异步发送：（fire-and-forget）

绝大多数情况下采用fire-and-forget模式发送消息，因为kafka本身的高可用以及客户端自动重试可以保证消息的正确发送。但这种方式有可能会丢消息（发送中的异常无法捕获）！

2）异步+回调：

Properties props = new Properties();
    props.put("bootstrap.servers", "10.39.16.34:9092");
    props.put("acks", "1");
    props.put("retries", 0);
    props.put("batch.size", 2);
    props.put("linger.ms", 10_000);
    //props.put("buffer.memory", 1024 * 1024 * 16);
    props.put("key.serializer","org.apache.kafka.common.serialization.StringSerializer");
    props.put("value.serializer","org.apache.kafka.common.serialization.StringSerializer");
    
    Producer<String, String> producer = new KafkaProducer<>(props);
    for (int i = 0; i < 100; i++) {
    	try {
    		producer.send(new ProducerRecord<>("test", Integer.toString(i), Integer.toString(i)), 
    			new Callback(){
    				@Override
    				public void onCompletion(RecordMetadata metadata,Exception exception) {//1
    					if (exception == null) {//2
    						System.out.println("Received new metadata." +
    								"Topic: " + metadata.topic()  + "," +
    								"Partition: " + metadata.partition() + "," +
    								"Offset: " + metadata.offset() + "," +
    								"Timestamp: " + metadata.timestamp());
    					} else {
    						logger.error("onCompletion error...",exception);
    					}
    				}
    		});
    	} catch (Exception e) {//3
    		logger.error("send error...",e);
    	}
    }
    
    //producer.close();

3）同步发送：

Properties props = new Properties();
    props.put("bootstrap.servers", "10.39.16.34:9092");
    props.put("acks", "1");
    props.put("retries", 0);
    props.put("batch.size", 5);
    props.put("linger.ms", 10_000);
    props.put("buffer.memory", 1024 * 1024 * 16);
    props.put("key.serializer","org.apache.kafka.common.serialization.StringSerializer");
    props.put("value.serializer","org.apache.kafka.common.serialization.StringSerializer");
    
    Producer<String, String> producer = new KafkaProducer<>(props);
    for (int i = 0; i < 100; i++) {
    	ProducerRecord<String, String> record = 
    			new ProducerRecord<>("test", Integer.toString(i), Integer.toString(i));
    	try {
    		RecordMetadata metadata = producer.send(record).get();//1
    		System.out.println("Received new metadata." +
    				"Topic: " + metadata.topic()  + "," +
    				"Partition: " + metadata.partition() + "," +
    				"Offset: " + metadata.offset() + "," +
    				"Timestamp: " + metadata.timestamp());
    	} catch(Exception e) {
    		logger.error("send error",e);//2
    	}
    }
    //producer.close();

注：send()方法本身不会抛出“发送中”的异常，会抛出发送前的异常（比如：序列化失败），对于发送中的异常信息捕获只能靠同步返回值（future.get()方法）、或者callback中的异常。

## 2、Callable中获取消息： ##

kafka是不会在producer的回调中，把发送的消息再一次返回回来的，因为这些消息我们可以自己记录，没必要浪费网络资源。上面的示例中我们看到，callback回调函数里只有metadata信息和Exception信息，当发送中出现异常，callback里改如何拿到消息做进一步处理呢？

继承Callback类，添加消息属性，在send的时候使用我们自己写的callback类。

1）继承callback：

class RecordCallback implements Callback {
    	private static final Logger logger = LoggerFactory.getLogger(RecordCallback.class); 
    	
    	private ProducerRecord<String,String> msg;
    	public RecordCallback(ProducerRecord<String,String> msg) {
    		this.msg = msg;
    	}
    	@Override
    	public void onCompletion(RecordMetadata metadata, Exception exception) {
    		if (exception == null) {//2
    			System.out.println("Received new metadata." +
                        "Topic: " + metadata.topic()  + "," +
                        "Partition: " + metadata.partition() + "," +
                        "Offset: " + metadata.offset() + "," +
                        "Timestamp: " + metadata.timestamp());
    		} else {
    			//将消息保存到日志
    			logger.info("save error msg,key:{},value:{}",msg.key(),msg.value());
    			logger.error("RecordCallback error...",exception);
    		}
    	}
    }

2）callbak发送消息：

Properties props = new Properties();
    props.put("bootstrap.servers", "10.39.16.34:9092");
    props.put("acks", "1");
    props.put("retries", 1);
    props.put("batch.size", 2);
    props.put("linger.ms", 10_000);
    //props.put("buffer.memory", 1024 * 1024 * 16);
    props.put("key.serializer","org.apache.kafka.common.serialization.StringSerializer");
    props.put("value.serializer","org.apache.kafka.common.serialization.StringSerializer");
    
    Producer<String, String> producer = new KafkaProducer<>(props);
    for (int i = 0; i < 100; i++) {
    	ProducerRecord<String, String> record = 
    			new ProducerRecord<>("test", Integer.toString(i), Integer.toString(i));
    	try {
    		producer.send(record, new RecordCallback(record));
    	} catch (Exception e) {//3
    		logger.error("send error...",e);
    	}
    }
    producer.close();

参考：[https://blog.csdn.net/wjlzx/article/details/103275541][https_blog.csdn.net_wjlzx_article_details_103275541]

总结：推荐使用callback模式

*  对于fire-and-forget模式，由于不会调用future.get()方法，所以对于一些异常无法捕获，从而会造成消息丢失；
 *  对于同步模式，性能很差，所以一般也不会使用；

[Producer API]: https://kafka.apache.org/documentation.html#producerapi
[Consumer API]: https://kafka.apache.org/documentation.html#consumerapi
[Streams API]: https://kafka.apache.org/documentation/streams
[Connector API]: https://kafka.apache.org/documentation.html#connect
[https_blog.csdn.net_wjlzx_article_details_103275541]: https://blog.csdn.net/wjlzx/article/details/103275541