kafka-python基本使用

作者:Zarten

知乎专栏:Python爬虫深入详解

知乎ID: Zarten

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kafka-python为Apache Kafka的python客户端。下面将介绍它的基本使用

1.Kafka及ZooKeeper的安装

这里将不累赘说明,参考 Apache Kafka

2.kafka-python的安装

pip3 install kafka-python

3.kafka-python的基本使用

  • 最简单使用实例

1.消费端

from kafka import KafkaConsumer

consumer = KafkaConsumer('my_topic', group_id= 'group2', bootstrap_servers= ['localhost:9092'])
for msg in consumer:
    print(msg)

  • 第1个参数为 topic的名称
  • group_id : 指定此消费者实例属于的组名,可以不指定
  • bootstrap_servers : 指定kafka服务器

2.生产端

from kafka import KafkaProducer

producer = KafkaProducer(bootstrap_servers=['localhost:9092'])
future = producer.send('my_topic' , key= b'my_key', value= b'my_value', partition= 0)
result = future.get(timeout= 10)
print(result)

producer.send函数为发送消息

  • 第1个参数为 topic名称,必须指定
  • key : 键,必须是字节字符串,可以不指定(但key和value必须指定1个),默认为None
  • value : 值,必须是字节字符串,可以不指定(但key和value必须指定1个),默认为None
  • partition : 指定发送的partition,由于kafka默认配置1个partition,固为0

future.get函数等待单条消息发送完成或超时,经测试,必须有这个函数,不然发送不出去,或用time.sleep代替

3.发送或接收消息解析

消费者端接收消息如下:

ConsumerRecord(topic='my_topic', partition=0, offset=4, timestamp=1529569531392, timestamp_type=0, key=b'my_value', value=None, checksum=None, serialized_key_size=8, serialized_value_size=-1)
  • topic
  • partition
  • offset : 这条消息的偏移量
  • timestamp : 时间戳
  • timestamp_type : 时间戳类型
  • key : key值,字节类型
  • value : value值,字节类型
  • checksum : 消息的校验和
  • serialized_key_size : 序列化key的大小
  • serialized_value_size : 序列化value的大小,可以看到value=None时,大小为-1

KafkaConsumer

  • 手动分配partition
from kafka import KafkaConsumer
from kafka import TopicPartition

consumer = KafkaConsumer(group_id= 'group2', bootstrap_servers= ['localhost:9092'])
consumer.assign([TopicPartition(topic= 'my_topic', partition= 0)])
for msg in consumer:
    print(msg)

  • 超时处理
from kafka import KafkaConsumer

consumer = KafkaConsumer('my_topic', group_id= 'group2', bootstrap_servers= ['localhost:9092'], consumer_timeout_ms=1000)
for msg in consumer:
    print(msg)

若不指定 consumer_timeout_ms,默认一直循环等待接收,若指定,则超时返回,不再等待

consumer_timeout_ms : 毫秒数

  • 订阅多个topic
from kafka import KafkaConsumer

consumer = KafkaConsumer(group_id= 'group2', bootstrap_servers= ['localhost:9092'])
consumer.subscribe(topics= ['my_topic', 'topic_1'])
for msg in consumer:
    print(msg)

可同时接收多个topic消息

也可用正则订阅一类topic

from kafka import KafkaConsumer
import json

consumer = KafkaConsumer(group_id= 'group2', bootstrap_servers= ['localhost:9092'], value_deserializer=lambda m: json.loads(m.decode('ascii')))
consumer.subscribe(pattern= '^my.*')
for msg in consumer:
    print(msg)

  • 解码json数据

编码(生产者):value_serializer

解码(消费者):value_deserializer

1.先看producer发送的json数据

from kafka import KafkaProducer
import json

producer = KafkaProducer(bootstrap_servers=['localhost:9092'], value_serializer=lambda m: json.dumps(m).encode('ascii'))
future = producer.send('my_topic' ,  value= {'value_1' : 'value_2'}, partition= 0)
future.get(timeout= 10)

2.consumer没有解码收到的数据

ConsumerRecord(topic='my_topic', partition=0, offset=22, timestamp=1529575016310, timestamp_type=0, key=None, value=b'{"value_1": "value_2"}', checksum=None, serialized_key_size=-1, serialized_value_size=22)

可以看到value为原始的json字节数据,接下来可以再做一步解码操作

3.consumer自动解码

from kafka import KafkaConsumer
import json

consumer = KafkaConsumer(group_id= 'group2', bootstrap_servers= ['localhost:9092'], value_deserializer=lambda m: json.loads(m.decode('ascii')))
consumer.subscribe(topics= ['my_topic', 'topic_1'])
for msg in consumer:
    print(msg)

接收结果:

ConsumerRecord(topic='my_topic', partition=0, offset=23, timestamp=1529575235994, timestamp_type=0, key=None, value={'value_1': 'value_2'}, checksum=None, serialized_key_size=-1, serialized_value_size=22)
  • 可以看到接收结果中,value已经自动解码,并为字符串类型
  • 不仅value可以json,key也可以,只需指定 key_deserializer

KafkaProducer

  • 发送字符串类型的key和value
from kafka import KafkaProducer

producer = KafkaProducer(bootstrap_servers=['localhost:9092'],key_serializer= str.encode, value_serializer= str.encode)
future = producer.send('my_topic' ,  key= 'key_3', value= 'value_3', partition= 0)
future.get(timeout= 10)

指定 key_serializer 和 value_serializer 为 str.encode,但消费者收到的还是字节字符串

若想要消费者收到的为字符串类型,就需要解码操作,key_deserializer= bytes.decode

from kafka import KafkaConsumer

consumer = KafkaConsumer(group_id= 'group2', bootstrap_servers= ['localhost:9092'], key_deserializer= bytes.decode, value_deserializer= bytes.decode)
consumer.subscribe(pattern= '^my.*')
for msg in consumer:
    print(msg)

  • 可压缩消息发送

compression_type=’gzip’

若消息过大,还可压缩消息发送,可选值为 ‘gzip’, ‘snappy’, ‘lz4’, or None

from kafka import KafkaProducer

producer = KafkaProducer(bootstrap_servers=['localhost:9092'], compression_type='gzip')
future = producer.send('my_topic' ,  key= b'key_3', value= b'value_3', partition= 0)
future.get(timeout= 10)

  • 发送msgpack消息

msgpack为MessagePack的简称,是高效二进制序列化类库,比json高效

producer = KafkaProducer(value_serializer=msgpack.dumps)
producer.send('msgpack-topic', {'key': 'value'})

参考文章

    原文作者:Zarten
    原文地址: https://zhuanlan.zhihu.com/p/38330574
    本文转自网络文章,转载此文章仅为分享知识,如有侵权,请联系博主进行删除。
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