January 2018
Beginner to intermediate
234 pages
7h 8m
Chinese
Content preview from Kafka权威指南
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管理
Kafka
｜
155
print.key
如果被设为 true，除了打印消息的值之外，还会打印消息的键。
key.separator
指定打印消息的键和消息的值所使用的分隔符。
line.separator
指定消息之间的分隔符。
key.deserializer
指定打印消息的键所使用的反序列化器类名。
value.deserializer
指定打印消息的值所使用的反序列化器类名。
反序列化类必须实现
org.apache.kafka.common.serialization.Deserializer
接口，控制
台消费者会调用它们的
toString()
方法获取输出结果。一般来说，在使用
kafka_console_
consumer.sh
工具之前，需要通过环境变量
CLASSPATH
将这些实现类添加到类路径里。
2.
读取偏移量主题
有时候，我们需要知道提交的消费者群组偏移量是多少，比如某个特定的群组是否在提交
偏移量，或者偏移量提交的频度。这个可以通过让控制台消费者读取一个特殊的内部主题
__consumer_offsets
来实现。所有消费者的偏移量都以消息的形式写到这个主题上。为了
解码这个主题的消息，需要使用
kafka.coordinator.GroupMetadataManager$OffsetsMessage
Formatter
这个格式化器。
示例：从偏移量主题读取一个消息。
# kafka-console-consumer.sh --zookeeper
zoo1.example.com:2181/kafka-cluster ...
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I'm always learning. So when I got on to O'Reilly, I was like a kid in a candy store. There are playlists. There are answers. There's on-demand training. It's worth its weight in gold, in terms of what it allows me to do.