为什么这个使用者（在servlet上运行）为什么没有收到来自kafka主题的消息？

Question

I've setted up an kafka-consumer on my servlet. 我已经在我的servlet上设置了kafka-consumer。 I read from my kafka topic and want to print the latest value using the doGet-method of the servlet. 我从kafka主题中阅读，并希望使用servlet的doGet方法打印最新值。

But if I send the doGet I just get a "null" back... 但是，如果我发送doGet，我将得到一个“空”的回信...

I'm not sure, but I found another post, where somebody mentioned, that this might be because there is no connection to the zookeeper servers. 我不确定，但是我发现了另一篇文章，有人提到这可能是因为与Zookeeper服务器没有连接。 So I tried to fix this adding the zookeeper.connection to the properties of the consumer; 因此，我尝试解决此问题，将zookeeper.connection添加到使用者的属性中； even if it's outdated. 即使已经过时。

Hopefully someone could give me advice about this. 希望有人可以给我一些建议。

Code of my Servlet: 我的Servlet代码：

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": 编辑：来自“ localhost.log”的最新日志文件：

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

I figured it out: the problem, why I did not receive any messages was the line props.put("bootstrap.servers", "localhost:9092"); 我发现了：问题，为什么我没有收到任何消息，是props.put("bootstrap.servers", "localhost:9092"); . 。

I had to change the "localhost" to my actual IP of my VM. 我必须将“ localhost”更改为虚拟机的实际IP。 This is kinda strange, because every other property I configured (on apache storm; kafka; another servlet which contains an kafka producer) was working well with "localhost". 这有点奇怪，因为我配置的所有其他属性（在Apache风暴中； kafka；另一个包含kafka生产者的servlet）在“ localhost”下运行良好。

为什么这个使用者（在servlet上运行）为什么没有收到来自kafka主题的消息？

问题描述

1 个解决方案

解决方案1
0 已采纳 2016-12-20 08:08:59

为什么这个使用者（在servlet上运行）为什么没有收到来自kafka主题的消息？

问题描述

1 个解决方案

解决方案1 0 已采纳 2016-12-20 08:08:59

解决方案1
0 已采纳 2016-12-20 08:08:59