kafka生产者

1、kafka生产者是线程安全的，她允许多个线程共享一个kafka实例

2、kafka管理一个简单的后台线程，所有的IO操作以及与每个broker的tcp连接通信，如果没有正确的关闭生产者可能会造成资源泄露。

kafka总共有以下的这些生产者实例

KafkaProducer(java.util.Map<java.lang.String,java.lang.Object> configs)
          A producer is instantiated by providing a set of key-value pairs as configuration.

KafkaProducer(java.util.Map<java.lang.String,java.lang.Object> configs, Serializer<K> keySerializer, Serializer<V> valueSerializer)
          A producer is instantiated by providing a set of key-value pairs as configuration, a key and a value Serializer.

KafkaProducer(java.util.Properties properties)
          A producer is instantiated by providing a set of key-value pairs as configuration.

KafkaProducer(java.util.Properties properties, Serializer<K> keySerializer, Serializer<V> valueSerializer)
          A producer is instantiated by providing a set of key-value pairs as configuration, a key and a value Serializer.

以及相应的方法

void	close()           Close this producer.
java.util.Map<MetricName,? extends Metric>	metrics()           Return a map of metrics maintained by the producer
java.util.List<PartitionInfo>	partitionsFor(java.lang.String topic)           Get a list of partitions for the given topic for custom partition assignment.
java.util.concurrent.Future<RecordMetadata>	send(ProducerRecord<K,V> record)           Asynchronously send a record to a topic.
java.util.concurrent.Future<RecordMetadata>	send(ProducerRecord<K,V> record, Callback callback)           Asynchronously send a record to a topic and invoke the provided callback when the send has been acknowledged.

主要介绍send方法

public java.util.concurrent.Future<RecordMetadata> send(ProducerRecord<K,V> record,
                                                        Callback callback)
send方法是异步的，消息到缓冲区后接着发送消息，不会确认数据是否已经存入kafka，调用callback函数有效的了解当send发送失败时能够抛出异常。