Apache kafka 在Kafka流中左加入时获取类强制转换异常

我正在浏览这里提到的示例：

我以json字符串的形式生成输入数据

用于主题-页面浏览

{"industry":"eng","user":"bob","page":"index.html"}

对于主题-用户配置文件

{"experience":"some","region":"europe"}

我的班级看起来像：

import com.google.gson.Gson;
import com.sohi.examples.dto.PageViews;
import com.sohi.examples.dto.UserProfiles;
import com.sohi.examples.dto.ViewsByRegion;
import org.apache.kafka.clients.consumer.ConsumerConfig;
import org.apache.kafka.common.serialization.Serde;
import org.apache.kafka.common.serialization.Serdes;
import org.apache.kafka.streams.KafkaStreams;
import org.apache.kafka.streams.KeyValue;
import org.apache.kafka.streams.StreamsConfig;
import org.apache.kafka.streams.kstream.*;

import java.io.IOException;
import java.util.Properties;


public class PageViewRegionLambdaExample {

    public static void main(String[] args) throws IOException {

        final String bootstrapServers = args.length > 0 ? args[0] : "localhost:9092";
        final Properties streamsConfiguration = new Properties();

        streamsConfiguration.put(StreamsConfig.APPLICATION_ID_CONFIG, "pageview-region-lambda-example");
        streamsConfiguration.put(StreamsConfig.BOOTSTRAP_SERVERS_CONFIG, bootstrapServers);
        streamsConfiguration.put(StreamsConfig.KEY_SERDE_CLASS_CONFIG, Serdes.String().getClass().getName());//NOSONAR
        streamsConfiguration.put(StreamsConfig.VALUE_SERDE_CLASS_CONFIG, Serdes.String().getClass().getName());//NOSONAR
        streamsConfiguration.put(ConsumerConfig.AUTO_OFFSET_RESET_CONFIG, "earliest");
        streamsConfiguration.put(StreamsConfig.COMMIT_INTERVAL_MS_CONFIG, 10 * 1000);


        final Serde<String> stringSerde = Serdes.String();//NOSONAR
        final Serde<Long> longSerde = Serdes.Long();//NOSONAR

        final KStreamBuilder builder = new KStreamBuilder();

        final KStream<String, String> views = builder.stream("PageViews");

        final KStream<String, PageViews> viewsByUser = views
                .map((dummy, record) -> new KeyValue<>(dummy, new Gson().fromJson(record, PageViews.class)))
                .map((dummy, record) -> {
                            System.out.println(record);
                            return new KeyValue<>(record.getUser(), record);
                        }
                );

        final KTable<String, String> userProfiles = builder.table("UserProfiles", "UserProfilesStore");
        final KTable<String, String> userRegions =
                userProfiles
                        .mapValues(record -> new Gson().fromJson(record, UserProfiles.class).getRegion());


        final KTable<Windowed<String>, Long> viewsByRegion =

                viewsByUser.leftJoin(userRegions, (view, region) -> {
                    ViewsByRegion viewRegion = new ViewsByRegion();
                    viewRegion.setUser(view.getUser());
                    viewRegion.setPage(view.getPage());
                    viewRegion.setRegion(region);
                    return viewRegion;
                })
                        .map((user, viewRegion) -> new KeyValue<>(viewRegion.getRegion(), ""))
                        .groupByKey()
                        .count(TimeWindows.of(5 * 60 * 1000L).advanceBy(60 * 1000L), "GeoPageViewsStore");


        final KStream<String, Long> viewsByRegionForConsole = viewsByRegion
                .toStream((windowedRegion, count) -> windowedRegion.toString());


        viewsByRegionForConsole.to(stringSerde, longSerde, "PageViewsByRegion");

        final KafkaStreams streams = new KafkaStreams(builder, streamsConfiguration);

        streams.cleanUp();
        streams.start();

        // Add shutdown hook to respond to SIGTERM and gracefully close Kafka Streams
        Runtime.getRuntime().addShutdownHook(new Thread(streams::close));

    }


}

---

如果我创建了自定义serde，我需要帮助了解在何处应用自定义serde。

您的自定义

serde

应在处理拓扑操作中使用。在本例中，它是-

leftJoin

，

groupByKey

。e、 g

pageviewserde pageviewserde=//实例化自定义Serde impl
viewsByUser.leftJoin（用户区域，（视图，区域）->{
ViewsByRegion viewRegion=新ViewsByRegion（）；
setUser（view.getUser（））；
setPage（view.getPage（））；
viewRegion.setRegion（区域）；
返回视图区域；
},
Serdes.String（），页面视图顺序
)

处理拓扑操作中应使用自定义的

Serde

。在本例中，它是-

leftJoin

，

groupByKey

。e、 g

pageviewserde pageviewserde=//实例化自定义Serde impl
viewsByUser.leftJoin（用户区域，（视图，区域）->{
ViewsByRegion viewRegion=新ViewsByRegion（）；
setUser（view.getUser（））；
setPage（view.getPage（））；
viewRegion.setRegion（区域）；
返回视图区域；
},
Serdes.String（），页面视图顺序
)

Exception in thread "StreamThread-1" org.apache.kafka.streams.errors.StreamsException: Exception caught in process. taskId=0_0, processor=KSTREAM-SOURCE-0000000000, topic=PageViews, partition=0, offset=44
    at org.apache.kafka.streams.processor.internals.StreamTask.process(StreamTask.java:216)
    at org.apache.kafka.streams.processor.internals.StreamThread.runLoop(StreamThread.java:641)
    at org.apache.kafka.streams.processor.internals.StreamThread.run(StreamThread.java:368)
Caused by: org.apache.kafka.streams.errors.StreamsException: A serializer (key: org.apache.kafka.common.serialization.StringSerializer / value: org.apache.kafka.common.serialization.StringSerializer) is not compatible to the actual key or value type (key type: java.lang.String / value type: com.sohi.examples.dto.PageViews). Change the default Serdes in StreamConfig or provide correct Serdes via method parameters.
    at org.apache.kafka.streams.processor.internals.SinkNode.process(SinkNode.java:81)
    at org.apache.kafka.streams.processor.internals.ProcessorContextImpl.forward(ProcessorContextImpl.java:83)
    at org.apache.kafka.streams.kstream.internals.KStreamFilter$KStreamFilterProcessor.process(KStreamFilter.java:44)
    at org.apache.kafka.streams.processor.internals.ProcessorNode$1.run(ProcessorNode.java:48)
    at org.apache.kafka.streams.processor.internals.StreamsMetricsImpl.measureLatencyNs(StreamsMetricsImpl.java:188)
    at org.apache.kafka.streams.processor.internals.ProcessorNode.process(ProcessorNode.java:134)
    at org.apache.kafka.streams.processor.internals.ProcessorContextImpl.forward(ProcessorContextImpl.java:83)
    at org.apache.kafka.streams.kstream.internals.KStreamMap$KStreamMapProcessor.process(KStreamMap.java:43)
    at org.apache.kafka.streams.processor.internals.ProcessorNode$1.run(ProcessorNode.java:48)
    at org.apache.kafka.streams.processor.internals.StreamsMetricsImpl.measureLatencyNs(StreamsMetricsImpl.java:188)
    at org.apache.kafka.streams.processor.internals.ProcessorNode.process(ProcessorNode.java:134)
    at org.apache.kafka.streams.processor.internals.ProcessorContextImpl.forward(ProcessorContextImpl.java:83)
    at org.apache.kafka.streams.kstream.internals.KStreamMap$KStreamMapProcessor.process(KStreamMap.java:43)
    at org.apache.kafka.streams.processor.internals.ProcessorNode$1.run(ProcessorNode.java:48)
    at org.apache.kafka.streams.processor.internals.StreamsMetricsImpl.measureLatencyNs(StreamsMetricsImpl.java:188)
    at org.apache.kafka.streams.processor.internals.ProcessorNode.process(ProcessorNode.java:134)
    at org.apache.kafka.streams.processor.internals.ProcessorContextImpl.forward(ProcessorContextImpl.java:83)
    at org.apache.kafka.streams.processor.internals.SourceNode.process(SourceNode.java:70)
    at org.apache.kafka.streams.processor.internals.StreamTask.process(StreamTask.java:197)
    ... 2 more
Caused by: java.lang.ClassCastException: com.sohi.examples.dto.PageViews cannot be cast to java.lang.String
    at org.apache.kafka.common.serialization.StringSerializer.serialize(StringSerializer.java:24)
    at org.apache.kafka.streams.processor.internals.RecordCollectorImpl.send(RecordCollectorImpl.java:78)
    at org.apache.kafka.streams.processor.internals.SinkNode.process(SinkNode.java:79)
    ... 20 more

Process finished with exit code 0