Question

我在我的servlet上设置了一个kafka-consumer。我从我的kafka主题中读取并希望使用servlet的doGet方法打印最新值。

但是如果我发送了doGet，我就会得到一个＆＃34; null＆＃34;回来...

我不确定，但我发现另一篇文章，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。

希望有人可以就此提出建议。

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();
    }
}}

编辑：来自＆＃34; localhost.log＆＃34;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

我明白了：问题，为什么我没有收到任何消息就是bin行。

我不得不改变＆＃34; localhost＆＃34;到我的VM的实际IP。这有点奇怪，因为我配置的每个其他属性（在apache风暴; kafka;另一个包含kafka生产者的servlet）与＆＃34; localhost＆＃34;一起运行良好。

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

1 个答案: