找不到Kafka生产者 - 组织

Question

我创建了一个简单的Kafka生产者

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();
}

}

启动捆绑包时，遇到以下错误：

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

我已尝试设置键。序列化程序和值。序列化程序如下所示：

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

也喜欢，但还是出现了同样的错误。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

问题似乎出在类加载器上，正如@Ram Ghadiyaram在他的回答中指出的那样。为了让它与kafka-client 2. x一起工作，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装入器装入其他类。这在《野蝇》/《JBoss》中是必需的（我正在使用的特定应用程序是键盘锁）。

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class Loader，它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;
}

所以，默认情况下，org.apache.kafka.common.serialization.StringSerializer的Class对象是由应用程序ClassLoader加载的，如果你的目标类没有被应用程序ClassLoader加载，就会出现这个问题！

要解决这个问题，只需在新的KafkaProducer实例之前将当前线程的ContextClassLoader设置为null，如下所示

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

希望我的回答能让你知道发生了什么。

Answer 3

这是您正在使用的版本的问题。也有人建议0.8.2.2_1版。建议你调整一下正在使用的Kafka版本，试试看。就代码而言，我交叉检查了kafka dev列表中的许多代码示例，看起来你的编写方式是正确的。

即< code>Thread.currentThread()。setContextClassLoader(null)；