String 卡夫卡消息键-字节[]和字符串同时出现

我对卡夫卡有一个非常困惑的问题——特别是试图获得一条信息的关键

键似乎认为它既是字符串又是字节[]

以下代码生成以下异常：

    Map<String, Integer> topicCount = new HashMap<>();
    topicCount.put(myConsumer.getTopic(), 1);

    Map<String, List<KafkaStream<byte[], byte[]>>> consumerStreams = myConsumer.getConsumer().createMessageStreams(topicCount);
    List<KafkaStream<byte[], byte[]>> streams = consumerStreams.get(myConsumer.getTopic());
    System.out.println("Listening to topic " + myConsumer.getTopic());
    for (final KafkaStream stream : streams) {
        ConsumerIterator<String, byte[]> it = stream.iterator();
        while (it.hasNext()) {

            System.out.println("Message received from topic");

            MessageAndMetadata<String, byte[]> o = it.next();

            Object messageKey = o.key();
            System.out.println("messageKey is type: " + messageKey.getClass().getName());
            System.out.println("messageKey is type: " + messageKey.getClass().getCanonicalName());
            System.out.println("o keyDecoder: " + o.keyDecoder());

            System.out.println("Key from message: " + o.key());  //This throws exception - [B cannot be cast to java.lang.String
            //System.out.println("Key as String: " + new String(o.key(), StandardCharsets.UTF_8));    //uncomment this compile Exception - no suitable constructor found for String(java.lang.String,java.nio.charset.Charset)

            byte[] bytesIn = o.message();       //getting the bytes is fine

            System.out.println("MessageAndMetadata: " + o);

            ///other code cut
        }
    }

马文：

<dependency>
  <groupId>org.apache.kafka</groupId>
  <artifactId>kafka_2.10</artifactId>
  <version>0.9.0.1</version>
</dependency>

为什么编译器认为键是一个字符串（这是我所期望的），而运行时它是一个字节数组

如何才能将密钥作为字符串获取

谢谢

---

KA.

这不匹配！将流声明为

KafkaStream

，然后期望

ConsumerIterator it=stream.iterator（）它应该是
ConsumerIterator it=stream.iterator（）以匹配泛型。然后您可以获取
o.key（）
并通过
newstring（o.key（））从中创建一个字符串
最好设置KafkaStream通用参数类型为（字节[]，字节[]）。尝试如下更改代码：

ConsumerIterator<byte[], byte[]> it = stream.iterator();
while (it.hasNext()) {
    String key = new String(it.next().key());
    ...
}

ConsumerIterator it=stream.iterator（）；
while（it.hasNext（））{
字符串键=新字符串（it.next（）.key（））；
...
}

[ERROR] COMPILATION ERROR :
[INFO] -------------------------------------------------------------
[ERROR] /C:/Dev/main/java/com/foo/bar/KafkaCFS.java:[152,56] no suitable constructor found for String(java.lang.String,java.nio.charset.Charset)
    constructor java.lang.String.String(byte[],int) is not applicable
    (argument mismatch; java.lang.String cannot be converted to byte[])

ConsumerIterator<byte[], byte[]> it = stream.iterator();
while (it.hasNext()) {
    String key = new String(it.next().key());
    ...
}