Question

我有两个Kafka Streams，其中包含String中的键和Avro格式的值，我使用KSQL创建。

这是第一个：

DESCRIBE EXTENDED STREAM_1; 
Type                 : STREAM
Key field            : IDUSER
Timestamp field      : Not set - using <ROWTIME>
Key format           : STRING
Value format         : AVRO
Kafka output topic   : STREAM_1 (partitions: 4, replication: 1)

 Field                      | Type
--------------------------------------------------------
 ROWTIME                    | BIGINT           (system)
 ROWKEY                     | VARCHAR(STRING)  (system)
 FIRSTNAME                  | VARCHAR(STRING)
 LASTNAME                   | VARCHAR(STRING)
 IDUSER                     | VARCHAR(STRING)

和第二个：

DESCRIBE EXTENDED STREAM_2;
Type                 : STREAM
Key field            : IDUSER
Timestamp field      : Not set - using <ROWTIME>
Key format           : STRING
Value format         : AVRO
Kafka output topic   : STREAM_2 (partitions: 4, replication: 1)

 Field                      | Type
--------------------------------------------------------
 ROWTIME                    | BIGINT           (system)
 ROWKEY                     | VARCHAR(STRING)  (system)
 USERNAME                   | VARCHAR(STRING)
 IDUSER                     | VARCHAR(STRING)
 DEVICE                     | VARCHAR(STRING)

所需的输出应包括IDUSER，LASTNAME，DEVICE和USERNAME。

我想使用Streams API left join这些流（在IDUSER上）并将输出写入kafka主题。

为此，我尝试了以下方法：

public static void main(String[] args) {

    final Properties streamsConfiguration = new Properties();

    streamsConfiguration.put(StreamsConfig.APPLICATION_ID_CONFIG, "kafka-strteams");
    streamsConfiguration.put(StreamsConfig.BOOTSTRAP_SERVERS_CONFIG, "localhost:9092");
    streamsConfiguration.put(StreamsConfig.ZOOKEEPER_CONNECT_CONFIG, "localhost:2181");
    streamsConfiguration.put(AbstractKafkaAvroSerDeConfig.SCHEMA_REGISTRY_URL_CONFIG, "http://localhost:8081");

    streamsConfiguration.put(StreamsConfig.KEY_SERDE_CLASS_CONFIG, Serdes.String().getClass().getName());
    streamsConfiguration.put(StreamsConfig.VALUE_SERDE_CLASS_CONFIG, GenericAvroSerde.class);
    streamsConfiguration.put(ConsumerConfig.AUTO_OFFSET_RESET_CONFIG, "earliest");

    final Serde<String> stringSerde = Serdes.String();
    final Serde<GenericRecord> genericAvroSerde = new GenericAvroSerde();


    boolean isKeySerde = false;
    genericAvroSerde.configure(Collections.singletonMap(AbstractKafkaAvroSerDeConfig.SCHEMA_REGISTRY_URL_CONFIG, "http://localhost:8081"), isKeySerde);

    KStreamBuilder builder = new KStreamBuilder();

    KStream<String, GenericRecord> left = builder.stream("STREAM_1");
    KStream<String, GenericRecord> right = builder.stram("STREAM_2");

    // Java 8+ example, using lambda expressions
    KStream<String, GenericRecord> joined = left.leftJoin(right,
        (leftValue, rightValue) -> "left=" + leftValue + ", right=" + rightValue, /* ValueJoiner */
        JoinWindows.of(TimeUnit.MINUTES.toMillis(5)),
        Joined.with(
          stringSerde, /* key */
          genericAvroSerde,   /* left value */
          genericAvroSerde)  /* right value */
      );
    joined.to(stringSerde, genericAvroSerde, "streams-output-testing");

    KafkaStreams streams = new KafkaStreams(builder, streamsConfiguration);
    streams.cleanUp();
    streams.start();

    Runtime.getRuntime().addShutdownHook(new Thread(streams::close));
}

然而，

KStream<String, GenericRecord> joined = ...

在我的IDE上抛出错误：

incompatible types: inference variable VR has incompatible bounds

当我尝试将String Serde用于键和值时，它可以正常工作，但数据不能从kafka-console-consumer读取。我想要做的是以AVRO格式生成数据，以便能够使用kafka-avro-console-consumer读取它们。

Answer 1

我的第一个猜测是你从联接操作返回String，而你的代码需要GenericRecord作为结果：

KStream<String, GenericRecord> joined = left.leftJoin(right,
    (leftValue, rightValue) -> "left=" + leftValue + ", right=" + rightValue, ...)

请注意joined类型KStream<String, GenericRecord>的方式，即值类型为GenericRecord，但是联接输出是通过"left=" + leftValue + ", right=" + rightValue计算的，其类型为String

Answer 2

您可以直接返回值，而不必将值转换为字符串。例如：

KStream joined = left.leftJoin(right,
(leftValue, rightValue) -> { return rightValue});

如何加入两个Kafka流并在Avro值

2 个答案: