kafka在java代码中如何写

Apache Kafka是一个分布式流处理平台，主要用于构建实时数据管道和发布/订阅消息系统。在Java中使用Kafka，首先需要添加依赖并创建配置。以下是一个简单的步骤概述：

1. **添加依赖**:
在Maven项目中，添加以下到`pom.xml`文件的`<dependencies>`部分：

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

2. **配置生产者** (发送消息):

   Properties props = new Properties();
   props.put("bootstrap.servers", "localhost:9092"); // Kafka集群地址
   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);
   producer.send(new ProducerRecord<>("test-topic", "message-key", "message-value"));
   producer.close();

3. **配置消费者** (接收消息):

   Properties consumerProps = new Properties();
   consumerProps.put("bootstrap.servers", "localhost:9092");
   consumerProps.put("group.id", "consumer-group"); // 消费组标识
   consumerProps.put("key.deserializer", "org.apache.kafka.common.serialization.StringDeserializer");
   consumerProps.put("value.deserializer", "org.apache.kafka.common.serialization.StringDeserializer");

   Consumer<String, String> consumer = new KafkaConsumer<>(consumerProps, new StringDeserializer(), new StringDeserializer());
   consumer.subscribe(Arrays.asList("test-topic"));

   while (true) {
       ConsumerRecords<String, String> records = consumer.poll(100); // 每隔100ms拉取一次
       for (ConsumerRecord<String, String> record : records)
           System.out.printf("offset = %d, key = %s, value = %s%n", record.offset(), record.key(), record.value());
   }

   consumer.close();

4. **高级特性** (如偏移量管理、事务等) 需要根据官方文档进一步学习。