Kafka-python如何消费json消息

Question

我是 Python 的新手，从 Kafka 开始。我有一个要求，我需要发送和使用 json 消息。为此，我使用 kafka-python 与 Kafka 进行通信。

#Producer.py
from kafka import KafkaProducer
import json
producer = KafkaProducer(bootstrap_servers='localhost:9092',value_serializer=lambda v: json.dumps(v).encode('utf-8'))
producer.send('offering_new', {"dataObjectID": "test1"})

#Consumer.py
import json
from kafka import KafkaConsumer
consumer = KafkaConsumer(bootstrap_servers='localhost:9092',auto_offset_reset='earliest', value_deserializer=lambda m: json.loads(m.decode('utf-8')))
consumer.subscribe(['offering_new'])
for message in consumer :
    print(message)

但是，我在消费者方面遇到以下异常：

Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "/home/paras/.local/lib/python3.6/site-packages/kafka/consumer/group.py", line 1111, in __next__
    return next(self._iterator)
  File "/home/paras/.local/lib/python3.6/site-packages/kafka/consumer/group.py", line 1082, in _message_generator
    for msg in self._fetcher:
  File "/home/paras/.local/lib/python3.6/site-packages/kafka/consumer/fetcher.py", line 482, in __next__
    return next(self._iterator)
  File "/home/paras/.local/lib/python3.6/site-packages/kafka/consumer/fetcher.py", line 388, in _message_generator
    self._next_partition_records = self._parse_fetched_data(completion)
  File "/home/paras/.local/lib/python3.6/site-packages/kafka/consumer/fetcher.py", line 799, in _parse_fetched_data
    unpacked = list(self._unpack_message_set(tp, records))
  File "/home/paras/.local/lib/python3.6/site-packages/kafka/consumer/fetcher.py", line 458, in _unpack_message_set
    tp.topic, record.value)
  File "/home/paras/.local/lib/python3.6/site-packages/kafka/consumer/fetcher.py", line 492, in _deserialize
    return f(bytes_)
  File "<stdin>", line 1, in <lambda>
  File "/usr/lib/python3.6/json/__init__.py", line 354, in loads
    return _default_decoder.decode(s)
  File "/usr/lib/python3.6/json/decoder.py", line 339, in decode
    obj, end = self.raw_decode(s, idx=_w(s, 0).end())
  File "/usr/lib/python3.6/json/decoder.py", line 357, in raw_decode
    raise JSONDecodeError("Expecting value", s, err.value) from None
json.decoder.JSONDecodeError: Expecting value: line 1 column 1 (char 0)

我是运行上面的代码在PythonShell。谁能告诉我哪里出错了？

Answer 1

在 auto_offset_reset='earliest' 中，您已将您的消费者配置为阅读该主题中的所有消息。 JSON 解码错误表明之前为主题生成的某些消息实际上不是 JSON 格式。

部分解决方案：

(1) 从主题的尾部开始消费：auto_offset_reset='latest'

(2) 开始新话题：consumer.subscribe(['offering_new_too'])

(3) 使用更全面的解串器：

def forgiving_json_deserializer(v):
    return if v is None
    try:
        return json.loads(v.decode('utf-8'))
    except json.decoder.JSONDecodeError:
        log.exception('Unable to decode: %s', v)
        return None

KafkaConsumer(value_deserializer=forgiving_json_deserializer, ...)

希望对您有所帮助！

Answer 2

确保您已遵循以下流程

pip install kafka-python

在 python 脚本中的 lib 下面导入

from kafka import KafkaConsumer
from json import loads

像下面这样创建 kafka 消费者对象

consumer = KafkaConsumer(
    'spring_test',
     bootstrap_servers=['localhost:9092'],
     auto_offset_reset='earliest',
     enable_auto_commit=True,
     group_id='my-group',
     value_deserializer=lambda x: loads(x.decode('utf-8')));

打印所有消息

for message in consumer:
    message = message.value;
    print('{}'.format(message))

希望这也能有所帮助

Kafka-python如何消费json消息

Kafka-python How to consume json message

python

python-3.x

apache-kafka

kafka-python