1

考虑以下代码：

public static long Offset = 0L;
FetchRequest req = new FetchRequest(KafkaProperties.topic, 0, Offset,10485760);
ByteBufferMessageSet messageSet = simpleConsumer.fetch(req);

问题是如何获取最后一个偏移量并设置回变量Offset以从 Kafka 读取下一批数据？

更新： 当我打印数据时，即：

for (MessageAndOffset messageAndOffset : messageSet) { 
            System.out.println(messageAndOffset);
}

输出如下：

MessageAndOffset(message(magic = 1, attributes = 0, crc = 2000130375, payload = java.nio.HeapByteBuffer[pos=0 lim=176 cap=176]),296215)
MessageAndOffset(message(magic = 1, attributes = 0, crc = 956398356, payload = java.nio.HeapByteBuffer[pos=0 lim=196 cap=196]),298144)
....
....
MessageAndOffset(message(magic = 1, attributes = 0, crc = 396743887, payload = java.nio.HeapByteBuffer[pos=0 lim=179 cap=179]),299136)

文档说最后一个数字是偏移量

MessageAndOffset(message: Message, offset: Long)

也就是说，在上述情况下，我最后一次读取的偏移量将是299136

4

1 回答 1

3

Does something like this help ? One bad thing about this is it will loop forever.

    long offset = 0;

    while (true) {
        FetchRequest fetchrequest = new FetchRequest(topicName, 0, offset, 10485760);

        ByteBufferMessageSet messages = consumer.fetch(fetchrequest);
        for (MessageAndOffset msg : messages) {
            System.out.println("consumed: " + Utils.toString(msg.message().payload(), "UTF-8"));
            offset = msg.offset();
        }

    }

Also in the 0.8 Kafka SimpleConsumer example, they have some thing like below 

    long numRead = 0;
    for (MessageAndOffset messageAndOffset : fetchResponse.messageSet(a_topic, a_partition)) {
          long currentOffset = messageAndOffset.offset();
          if (currentOffset < readOffset) {
             System.out.println("Found an old offset: " + currentOffset + " Expecting: " + readOffset);
             continue;
          }
          readOffset = messageAndOffset.nextOffset();
          ByteBuffer payload = messageAndOffset.message().payload();

          byte[] bytes = new byte[payload.limit()];
          payload.get(bytes);
          System.out.println(String.valueOf(messageAndOffset.offset()) + ": " + new String(bytes, "UTF-8"));
          numRead++;
          a_maxReads--;
    }

But they also mentioned that the application expects the a_maxread(Maximum number of messages to read) parameter to be passed as an argument so we don’t loop forever. I am new to kafka and not sure if this is what you are looking for.

于 2013-08-19T09:22:59.973 回答