为什么这个消费者（运行在 servlet 上）没有收到来自 kafka 主题的任何消息？

Question

我已经在我的 servlet 上设置了一个 kafka-consumer。我阅读了我的 kafka 主题并想使用 servlet 的 doGet 方法打印最新值。

但是如果我发送 doGet，我只会得到 "null" 返回...

我不确定，但我发现了另一个 post，其中有人提到，这可能是因为没有与 zookeeper 服务器的连接。所以我试图解决这个问题，将 zookeeper.connection 添加到消费者的属性中；即使它已经过时了。

希望有人能给我一些建议。

Code of my Servlet:

public class KafkaServlet extends HttpServlet implements Runnable {

public String kafkaMessage;
private Properties props;
private KafkaConsumer<String, String> consumer;
Thread Trans;

/**
*   setting up the properties and other consumer using the constructor of KafkaServlet
*/
public KafkaServlet() {
    props = new Properties();
    props.put("bootstrap.servers", "localhost:9092"); //replace 'localhost' with the actual IP to get it working.
    props.put("zookeeper.connect", "localhost:2181");
    props.put("auto.offset.reset", "earliest");
    props.put("key.deserializer", "org.apache.kafka.common.serialization.StringDeserializer");
    props.put("value.deserializer", "org.apache.kafka.common.serialization.StringDeserializer");
    consumer = new KafkaConsumer<>(props);
    consumer.subscribe(Arrays.asList("kafkaTopic"));
}

/**
*   setup the thread and run it using the init-method
*/
@Override
public void init (ServletConfig config) throws ServletException {
    super.init(config);
    Trans = new Thread(this);
    Trans.setPriority(Thread.MIN_PRIORITY);
    Trans.start();
}

/**
*   implement the doPost-Method if we want to use it 
*/
public void doPost(HttpServletRequest req, HttpServletResponse res) throws ServletException, IOException {
    //empty -- nothing to post here
}

/**
*   doGet will get print out our returned message from kafka
*/
@Override
public void doGet(HttpServletRequest req, HttpServletResponse res) throws ServletException, IOException {

res.setContentType("text/html");
PrintWriter out = res.getWriter();
String title = "Reading Parameters from kafkaTopic";

out.println("<HTML>" +
            "<BODY>\n" +
            "<H1 ALIGN=CENTER>" + title + "</H1>\n" +
            "<UL>\n" +
            "  <LI>MESSAGE: "
            + kafkaMessage + "\n" +
            "</UL>\n" +
            "</BODY></HTML>");
}

/**
*   thread, which grabs the messages from kafka and stores the latest one in "kafkaMessage"
*/
@Override
public void run() {
    try {
        while (true) {
            ConsumerRecords<String, String> records = consumer.poll(100);
            for (ConsumerRecord<String, String> record : records) {
                //KafkaMessage.setMessage(record.value());
                kafkaMessage = record.value();
            }
        }
    } catch (Exception e) {
        e.printStackTrace();
    } finally {
        consumer.close();
    }
}}

EDIT: Latest logfiles from "localhost.log":

19-Dec-2016 13:42:42.773 INFO [localhost-startStop-2] org.apache.catalina.core.ApplicationContext.log SessionListener: contextDestroyed() 19-Dec-2016 13:42:42.774 INFO [localhost-startStop-2] org.apache.catalina.core.ApplicationContext.log ContextListener: contextDestroyed() 19-Dec-2016 13:42:54.742 INFO [localhost-startStop-1] org.apache.catalina.core.ApplicationContext.log ContextListener: contextInitialized() 19-Dec-2016 13:42:54.745 INFO [localhost-startStop-1] org.apache.catalina.core.ApplicationContext.log SessionListener: contextInitialized()

Answer 1

我想通了：问题，为什么我没有收到任何消息是行 props.put("bootstrap.servers", "localhost:9092");。

我不得不将 "localhost" 更改为我的 VM 的实际 IP。这有点奇怪，因为我配置的所有其他属性（在 apache 风暴；kafka；另一个包含 kafka 生产者的 servlet）在 "localhost".

下运行良好

为什么这个消费者（运行在 servlet 上）没有收到来自 kafka 主题的任何消息？

Why does this consumer (running on a servlet) not receive any messages from the kafka topic?

java

servlets

apache-kafka

consumer

为什么这个消费者（运行 在 servlet 上）没有收到来自 kafka 主题的任何消息？

Why does this consumer (running on a servlet) not receive any messages from the kafka topic?

java

servlets

apache-kafka

consumer

为什么这个消费者（运行在 servlet 上）没有收到来自 kafka 主题的任何消息？