在Kafka消费者API中实现Deserializer和Serde有什么区别？

Question

我尝试在GitHub（https://github.com/onurtokat/kafka-clickstream-enrich）上模拟Gwen（Chen）Shapira的kafka-clickstream-rich kafka-stream项目。当我使用反序列化器使用消费者类消费一个主题时，我遇到了一个错误。自定义的Serde类有序列化器和反序列化器。但是，我试图理解为什么自定义serde用于反序列化器，然后消费者API给出了错误，因为它不是org.apache.kafka.common.serialization.Deserializer的实例

该主题可以使用带有Serdes的KTable。Integer（）序列化器和新的ProfileSerde（）反序列化器，如下所示。

KTable<Integer, UserProfile> profiles = builder.table(Constants.USER_PROFILE_TOPIC,
                Consumed.with(Serdes.Integer(), new ProfileSerde()),
                Materialized.as("profile-store"));

定制塞尔德被定义为;

static public final class ProfileSerde extends WrapperSerde<UserProfile> {
        public ProfileSerde() {
            super(new JsonSerializer<UserProfile>(), new JsonDeserializer<UserProfile>(UserProfile.class));
        }
    }

和通用Serde定制喜欢下面；

package com.onurtokat.serde;

import org.apache.kafka.common.serialization.Deserializer;
import org.apache.kafka.common.serialization.Serde;
import org.apache.kafka.common.serialization.Serializer;

import java.util.Map;


public class WrapperSerde<T> implements Serde<T> {

    final private Serializer<T> serializer;
    final private Deserializer<T> deserializer;

    public WrapperSerde(Serializer<T> serializer, Deserializer<T> deserializer) {
        this.serializer = serializer;
        this.deserializer = deserializer;
    }

    @Override
    public void configure(Map<String, ?> configs, boolean isKey) {
        serializer.configure(configs, isKey);
        deserializer.configure(configs, isKey);
    }

    @Override
    public void close() {
        serializer.close();
        deserializer.close();
    }

    @Override
    public Serializer<T> serializer() {
        return serializer;
    }

    @Override
    public Deserializer<T> deserializer() {
        return deserializer;
    }
}

我的消费就是这么简单，下面就能看出来；

package com.onurtokat.consumers;

import com.onurtokat.ClickstreamEnrichment;
import com.onurtokat.Constants;
import com.onurtokat.model.UserProfile;
import org.apache.kafka.clients.consumer.ConsumerConfig;
import org.apache.kafka.clients.consumer.ConsumerRecord;
import org.apache.kafka.clients.consumer.ConsumerRecords;
import org.apache.kafka.clients.consumer.KafkaConsumer;
import org.apache.kafka.common.serialization.IntegerDeserializer;

import java.time.Duration;
import java.util.Arrays;
import java.util.Properties;

public class ConsumeProfileData {

    public static void main(String[] args) {
        //prepare config
        Properties config = new Properties();
        config.put(ConsumerConfig.BOOTSTRAP_SERVERS_CONFIG, "localhost:9092");
        config.put(ConsumerConfig.KEY_DESERIALIZER_CLASS_CONFIG, IntegerDeserializer.class.getName());
        config.put(ConsumerConfig.VALUE_DESERIALIZER_CLASS_CONFIG, ClickstreamEnrichment.ProfileSerde.class);

        KafkaConsumer<Integer, UserProfile> consumerProfileTopic = new KafkaConsumer<>(config);
        consumerProfileTopic.subscribe(Arrays.asList(Constants.USER_PROFILE_TOPIC));
        while (true) {
            ConsumerRecords<Integer, UserProfile> records = consumerProfileTopic.poll(Duration.ofMillis(100));
            for (ConsumerRecord<Integer, UserProfile> record : records) {
                System.out.println(record.key() + " " + record.value());
            }
        }
    }
}

当我尝试与我的消费者消费主题时，错误是；

log4j:WARN No appenders could be found for logger (org.apache.kafka.clients.consumer.ConsumerConfig).
log4j:WARN Please initialize the log4j system properly.
log4j:WARN See http://logging.apache.org/log4j/1.2/faq.html#noconfig for more info.
Exception in thread "main" org.apache.kafka.common.KafkaException: Failed to construct kafka consumer
    at org.apache.kafka.clients.consumer.KafkaConsumer.<init>(KafkaConsumer.java:811)
    at org.apache.kafka.clients.consumer.KafkaConsumer.<init>(KafkaConsumer.java:659)
    at org.apache.kafka.clients.consumer.KafkaConsumer.<init>(KafkaConsumer.java:639)
    at com.onurtokat.consumers.ConsumeProfileData.main(ConsumeProfileData.java:25)
Caused by: org.apache.kafka.common.KafkaException: com.onurtokat.ClickstreamEnrichment$ProfileSerde is not an instance of org.apache.kafka.common.serialization.Deserializer
    at org.apache.kafka.common.config.AbstractConfig.getConfiguredInstance(AbstractConfig.java:304)
    at org.apache.kafka.clients.consumer.KafkaConsumer.<init>(KafkaConsumer.java:712)
    ... 3 more

Answer 1

看来你误解了：

可以使用带有Serdes.Integer（）序列化器和新ProfileSerde（）反序列化器的KTable来使用该主题，如下所示。

您必须为Consumed.with（）提供KeySerde和ValueSerde。

关于例外：

非常清楚——您必须设置反序列化器(不是Serde)的实现

config.put(ConsumerConfig.VALUE_DESERIALIZER_CLASS_CONFIG, //here);

Answer 2

不同的是:

< li>Serdes由Kafka的Streams API(也称为Kafka Streams)使用。Serde是同一数据类型的一对(1)序列化程序和(2)反序列化程序的包装器——参见下面两个要点。即一个< code>Serde

关于：

Caused by: org.apache.kafka.common.KafkaException: com.onurtokat.ClickstreamEnrichment$ProfileSerde is not an instance of org.apache.kafka.common.serialization.Deserializer
    at org.apache.kafka.common.config.AbstractConfig.getConfiguredInstance(AbstractConfig.java:304)
    at org.apache.kafka.clients.consumer.KafkaConsumer.<init>(KafkaConsumer.java:712)
    ... 3 more

您的 Kafka 消费者客户端代码被赋予了 Serde，它期望有一个解串器。