无法找到Kafka Producer - org.apache.kafka.common.serialization.StringSerializer

Question

我创造了一个简单的Kafka Producer＆amp;消费者。我正在使用kafka_2.11-0.9.0.0。这是我的制作人代码，

public class KafkaProducerTest {
public static String topicName = "test-topic-2";
public static void main(String[] args) {
    // TODO Auto-generated method stub
    Properties props = new Properties();
    props.put("bootstrap.servers", "localhost:9092");
    props.put("acks", "all");
    props.put("retries", 0);
    props.put("batch.size", 16384);
    props.put("linger.ms", 1);
    props.put("buffer.memory", 33554432);
    props.put("key.serializer",
            StringSerializer.class.getName());
    props.put("value.serializer",
            StringSerializer.class.getName());

    Producer<String, String> producer = new KafkaProducer(props);
    for (int i = 0; i < 100; i++) {
        ProducerRecord<String, String> producerRecord = new ProducerRecord<String, String>(
                topicName, Integer.toString(i), Integer.toString(i));
        System.out.println(producerRecord);
        producer.send(producerRecord);
    }

    producer.close();
}

}

启动捆绑时，我面临以下错误，

2016-05-20 09:44:57,792 | ERROR | nsole user karaf | ShellUtil                        | 44 - org.apache.karaf.shell.core - 4.0.3 | Exception caught while executing command
org.apache.karaf.shell.support.MultiException: Error executing command on bundles:
    Error starting bundle162: Activator start error in bundle NewKafkaArtifact [162].
    at org.apache.karaf.shell.support.MultiException.throwIf(MultiException.java:61)
    at org.apache.karaf.bundle.command.BundlesCommand.doExecute(BundlesCommand.java:69)[24:org.apache.karaf.bundle.core:4.0.3]
    at org.apache.karaf.bundle.command.BundlesCommand.execute(BundlesCommand.java:54)[24:org.apache.karaf.bundle.core:4.0.3]
    at org.apache.karaf.shell.impl.action.command.ActionCommand.execute(ActionCommand.java:83)[44:org.apache.karaf.shell.core:4.0.3]
    at org.apache.karaf.shell.impl.console.osgi.secured.SecuredCommand.execute(SecuredCommand.java:67)[44:org.apache.karaf.shell.core:4.0.3]
    at org.apache.karaf.shell.impl.console.osgi.secured.SecuredCommand.execute(SecuredCommand.java:87)[44:org.apache.karaf.shell.core:4.0.3]
    at org.apache.felix.gogo.runtime.Closure.executeCmd(Closure.java:480)[44:org.apache.karaf.shell.core:4.0.3]
    at org.apache.felix.gogo.runtime.Closure.executeStatement(Closure.java:406)[44:org.apache.karaf.shell.core:4.0.3]
    at org.apache.felix.gogo.runtime.Pipe.run(Pipe.java:108)[44:org.apache.karaf.shell.core:4.0.3]
    at org.apache.felix.gogo.runtime.Closure.execute(Closure.java:182)[44:org.apache.karaf.shell.core:4.0.3]
    at org.apache.felix.gogo.runtime.Closure.execute(Closure.java:119)[44:org.apache.karaf.shell.core:4.0.3]
    at org.apache.felix.gogo.runtime.CommandSessionImpl.execute(CommandSessionImpl.java:94)[44:org.apache.karaf.shell.core:4.0.3]
    at org.apache.karaf.shell.impl.console.ConsoleSessionImpl.run(ConsoleSessionImpl.java:270)[44:org.apache.karaf.shell.core:4.0.3]
    at java.lang.Thread.run(Thread.java:745)[:1.8.0_66]
Caused by: java.lang.Exception: Error starting bundle162: Activator start error in bundle NewKafkaArtifact [162].
    at org.apache.karaf.bundle.command.BundlesCommand.doExecute(BundlesCommand.java:66)[24:org.apache.karaf.bundle.core:4.0.3]
    ... 12 more
Caused by: org.osgi.framework.BundleException: Activator start error in bundle NewKafkaArtifact [162].
    at org.apache.felix.framework.Felix.activateBundle(Felix.java:2276)[org.apache.felix.framework-5.4.0.jar:]
    at org.apache.felix.framework.Felix.startBundle(Felix.java:2144)[org.apache.felix.framework-5.4.0.jar:]
    at org.apache.felix.framework.BundleImpl.start(BundleImpl.java:998)[org.apache.felix.framework-5.4.0.jar:]
    at org.apache.karaf.bundle.command.Start.executeOnBundle(Start.java:38)[24:org.apache.karaf.bundle.core:4.0.3]
    at org.apache.karaf.bundle.command.BundlesCommand.doExecute(BundlesCommand.java:64)[24:org.apache.karaf.bundle.core:4.0.3]
    ... 12 more
Caused by: org.apache.kafka.common.config.ConfigException: Invalid value org.apache.kafka.common.serialization.StringSerializer for configuration key.serializer: Class org.apache.kafka.common.serialization.StringSerializer could not be found.
    at org.apache.kafka.common.config.ConfigDef.parseType(ConfigDef.java:255)[141:kafka-examples:1.0.0.SNAPSHOT-jar-with-dependencies]
    at org.apache.kafka.common.config.ConfigDef.parse(ConfigDef.java:145)[141:kafka-examples:1.0.0.SNAPSHOT-jar-with-dependencies]
    at org.apache.kafka.common.config.AbstractConfig.<init>(AbstractConfig.java:49)[141:kafka-examples:1.0.0.SNAPSHOT-jar-with-dependencies]
    at org.apache.kafka.common.config.AbstractConfig.<init>(AbstractConfig.java:56)[141:kafka-examples:1.0.0.SNAPSHOT-jar-with-dependencies]
    at org.apache.kafka.clients.producer.ProducerConfig.<init>(ProducerConfig.java:317)[141:kafka-examples:1.0.0.SNAPSHOT-jar-with-dependencies]
    at org.apache.kafka.clients.producer.KafkaProducer.<init>(KafkaProducer.java:181)[141:kafka-examples:1.0.0.SNAPSHOT-jar-with-dependencies]
    at com.NewKafka.NewKafkaArtifact.KafkaProducerTest.main(KafkaProducerTest.java:25)[162:NewKafkaArtifact:0.0.1.SNAPSHOT]
    at com.NewKafka.NewKafkaArtifact.StartKafka.start(StartKafka.java:11)[162:NewKafkaArtifact:0.0.1.SNAPSHOT]
    at org.apache.felix.framework.util.SecureAction.startActivator(SecureAction.java:697)[org.apache.felix.framework-5.4.0.jar:]
    at org.apache.felix.framework.Felix.activateBundle(Felix.java:2226)[org.apache.felix.framework-5.4.0.jar:]
    ... 16 more

我尝试过设置key.serializer和value.serializer，如下所示，

props.put("key.serializer",StringSerializer.class.getName());
props.put("value.serializer",StringSerializer.class.getName());

也喜欢，但仍然得到同样的错误。我在这里做错了什么。

props.put("key.serializer", "org.apache.kafka.common.serialization.StringSerializer");
props.put("value.serializer", "org.apache.kafka.common.serialization.StringSerializer");

Answer 1

您使用的版本存在问题。 还建议版本为0.8.2.2_1。 建议你调整你正在使用的kafka的版本并试一试。 代码方面，我在kafka开发列表中交叉检查了许多代码示例，看起来你已经以正确的方式编写了。

即Thread.currentThread().setContextClassLoader(null);

Answer 2

我通过阅读kafka客户端源代码找到了原因。

kafka客户端使用Class.forName(trimmed, true, Utils.getContextOrKafkaClassLoader())获取Class对象，并创建实例，关键点是classLoader，由最后一个参数指定，方法Utils.getContextOrKafkaClassLoader()的实现是

public static ClassLoader getContextOrKafkaClassLoader() {
    ClassLoader cl = Thread.currentThread().getContextClassLoader();
    if (cl == null)
        return getKafkaClassLoader();
    else
        return cl;
}

因此，默认情况下，org.apache.kafka.common.serialization.StringSerializer的Class对象是由applicationClassLoader加载的，如果目标类不是由applicationClassLoader加载的，则会发生此问题！

要解决该问题，只需在这样的新KafkaProducer实例之前将当前线程的ContextClassLoader设置为null

Thread.currentThread().setContextClassLoader(null);
Producer<String, String> producer = new KafkaProducer(props);

希望我的回答可以让您知道发生了什么事。

Answer 3

最近我找到了解决方案。将Thead Context loader设置为null为我解决了这个问题。感谢。

Thread.currentThread().setContextClassLoader(null);
Producer<String, String> producer = new KafkaProducer(props);

Answer 4

问题似乎与类加载器有关，如@Ram Ghadiyaram在其答案中指出的那样。为了使它与kafka-clients 2.x兼容，我必须执行以下操作：

public Producer<String, String> createProducer() {
            ClassLoader original = Thread.currentThread().getContextClassLoader();
    Thread.currentThread().setContextClassLoader(null);
    Properties props = new Properties();

    props.put(ProducerConfig.BOOTSTRAP_SERVERS_CONFIG,
        BOOTSTRAP_SERVERS);
    ... etc ...

    KafkaProducer<String, String> producer = new KafkaProducer<>(props);
    Thread.currentThread().setContextClassLoader(original);
    return producer;

}

这允许系统继续使用原始类加载器加载其他类。这在Wildfly / JBoss（我正在使用的特定应用是Keycloak）中是必需的。

Answer 5

尝试使用这些道具代替您的道具。

  props.put("key.serializer", 
         "org.apache.kafka.common.serialization.StringSerializer");

  props.put("value.serializer", 
         "org.apache.kafka.common.serialization.StringSerializer");

这里是完整的Kafka Producer示例：-

import java.util.Properties; 
import org.apache.kafka.clients.producer.Producer;    
import org.apache.kafka.clients.producer.KafkaProducer;
import org.apache.kafka.clients.producer.ProducerRecord;
public class FxDateProducer {

   public static void main(String[] args) throws Exception{

      if(args.length == 0){
         System.out.println("Enter topic name”);
         return;
      }

      String topicName = args[0].toString(); 
      Properties props = new Properties();

      //Assign localhost id
      props.put("bootstrap.servers", “localhost:9092");

      //Set acknowledgements for producer requests.      
      props.put("acks", “all");

      //If the request fails, the producer can automatically retry,
      props.put("retries", 0);

      //Specify buffer size in config
      props.put("batch.size", 16384);

      //Reduce the no of requests less than 0   
      props.put("linger.ms", 1);

      //The buffer.memory controls the total amount of memory available to the producer for buffering.   
      props.put("buffer.memory", 33554432);

      props.put("key.serializer", 
         "org.apache.kafka.common.serialization.StringSerializer");

      props.put("value.serializer", 
         "org.apache.kafka.common.serialization.StringSerializer");

      Producer<String, String> producer = new KafkaProducer
         <String, String>(props);

      for(int i = 0; i < 10; i++)
         producer.send(new ProducerRecord<String, String>(topicName, 
            Integer.toString(i), Integer.toString(i)));
               System.out.println(“Message sent successfully”);
               producer.close();
   }
}

Answer 6

由于kafka版本问题而发生。确保使用正确的kafka版本。我使用的版本是'kafka_2.12-1.0.1'

但是尝试在代码中使用以下属性。这解决了我的问题。

randomSeed( analogRead(pinNum) );

我以前使用的是以下导致问题的属性。

props.put(ProducerConfig.VALUE_SERIALIZER_CLASS_CONFIG,"org.apache.kafka.common.serialization.StringSerializer");
props.put(ProducerConfig.KEY_SERIALIZER_CLASS_CONFIG,"org.apache.kafka.common.serialization.StringSerializer");