kafka学习（四）--java开发(基于kafka0.9版本)

kafka-clients jar包采用的是org.apache.kafka:kafka-clients:0.9.0.1。

Producer

Properties props = new Properties();
props.put("bootstrap.servers", "x.x.x.x:9091");
props.put("key.serializer", "org.apache.kafka.common.serialization.StringSerializer");
props.put("value.serializer", "org.apache.kafka.common.serialization.StringSerializer");
props.put("acks", "all");
props.put("retries", 1);

Producer<String, String> producer = new KafkaProducer<String, String>(props);
producer.send(new ProducerRecord<String, String>(topic, "Hello"));

producer.send(new ProducerRecord<String, String>(topic, "World"), new Callback() {
    @Override
    public void onCompletion(RecordMetadata metadata, Exception e) {
        if (e != null) {
            e.printStackTrace();
        } else {
            System.out.println(metadata.toString());//org.apache.kafka.clients.producer.RecordMetadata@1d89e2b5
            System.out.println(metadata.offset());//1
        }
    }
});
producer.flush();
producer.close();

Consumer

Properties props = new Properties();
props.put("bootstrap.servers", " x.x.x.x:9091");
props.put("key.deserializer", "org.apache.kafka.common.serialization.StringDeserializer");
props.put("value.deserializer", "org.apache.kafka.common.serialization.StringDeserializer");
props.setProperty("group.id", "0");
props.setProperty("enable.auto.commit", "true");
props.setProperty("auto.offset.reset", "earliest");

Consumer<String, String> consumer = new KafkaConsumer<String, String>(props);
consumer.subscribe(Lists.newArrayList(topic));

for (int i = 0; i < 2; i++) {
    ConsumerRecords<String, String> records = consumer.poll(1000);
    System.out.println(records.count());
    for (ConsumerRecord<String, String> record : records) {
        System.out.println(record);
        //consumer.seekToBeginning(new TopicPartition(record.topic(), record.partition()));
    }
}

注意，auto.offset.reset这里设置为earliest，是为了consumer能够从头开始读取内容即offset=0开始。默认是最新的offset开始读取（即当前最大的offset开始）。consumer.seekToBeginning也可以设置offset，但是跟源码发现，This function evaluates lazily, seeking to the final offset in all partitions only when {@link #poll(long)} or {@link #position(TopicPartition)} are called.也就是说seekToBeginning()的设置要生效的话，必须在poll或则position方法调用后设置seekToBeginning()才行。