Why does Kafka consumer throw "java.lang.NoClassDefFoundError: kafka/consumer/ConsumerConfig" at startup?

Question

我正在试用 apache 网站中给出的示例中的基本消费者代码。编译没问题。但是我在运行使用命令 java -jar target/JarName.jar:

时得到 ClassNotFoundException

Exception in thread "main" java.lang.NoClassDefFoundError: kafka/consumer/ConsumerConfig
    at com.package.ConsumerClass.functionConsumer(ConsumerClass.java:41)
    at com.package.App.main(App.java:26)
Caused by: java.lang.ClassNotFoundException: kafka.consumer.ConsumerConfig
    at java.net.URLClassLoader.run(URLClassLoader.java:366)
    at java.net.URLClassLoader.run(URLClassLoader.java:355)
    at java.security.AccessController.doPrivileged(Native Method)
    at java.net.URLClassLoader.findClass(URLClassLoader.java:354)
    at java.lang.ClassLoader.loadClass(ClassLoader.java:425)
    at sun.misc.Launcher$AppClassLoader.loadClass(Launcher.java:308)
    at java.lang.ClassLoader.loadClass(ClassLoader.java:358)

源代码是

package com.package;
import java.util.HashMap;
import java.util.Properties;
import java.util.Map;
import java.util.List;
import java.lang.Object;
import kafka.consumer.Consumer;
import kafka.consumer.ConsumerConfig;
import kafka.consumer.ConsumerConnector;
import kafka.consumer.ConsumerIterator;
import kafka.consumer.KafkaStream;
public class ExampleConsumer {
    public void exampleConsumer(){
        Properties props = new Properties();
        props.put("zk.connect", "localhost:2181");
        props.put("zk.connectiontimeout.ms", "1000000");
        props.put("groupid", "test_group");

        ConsumerConfig consumerConfig = new ConsumerConfig(props);
        ConsumerConnector consumerConnector = (ConsumerConnector) Consumer.createJavaConsumerConnector(consumerConfig);

        Map<String, Object> topicCountMap = new HashMap<String, Object>();
        topicCountMap.put("test", new Integer(1));
        Map<String, List<KafkaStream<byte[], byte[]>>> consumerMap = (Map<String, List<KafkaStream<byte[], byte[]>>>) consumerConnector.createMessageStreams((scala.collection.Map<String, Object>) topicCountMap);
        KafkaStream<byte[], byte[]> stream = consumerMap.get("test").get(0);
        ConsumerIterator<byte[], byte[]> it = stream.iterator();
        while(it.hasNext())
            System.out.println(new String(it.next().message()));
    }
}

我正在使用 Maven 来解决依赖关系。 pom.xml 的依赖部分看起来像这样

<dependency>
        <groupId>org.apache.kafka</groupId>
        <artifactId>kafka_2.10</artifactId>
        <version>0.8.2.1</version>
        <scope>compile</scope>
</dependency>
        <dependency>
                <groupId>org.apache.kafka</groupId>     
                <artifactId>kafka-clients</artifactId>
                <version>0.8.2.1</version>
                <scope>compile</scope>
        </dependency>

我正在使用 kafka_2.10-0.8.2.1 版本。欢迎任何建议。

Answer 1

java -jar target/JarName.jar 在 JarName.jar 中运行 Main-Class 而没有像 Kafka 那样的 依赖项。由于您的应用程序确实需要类路径上的依赖项 jars，您应该使用 How can I create an executable JAR with dependencies using Maven? 中解释的解决方案或自己构建类路径。

BTW 跟Kafka没关系，你开发客户端就行了

p.s。考虑使用 Scala 和 sbt（或者 gradle），你的生活会变得更加轻松。

Answer 2

为什么要使用 kafka.consumer.ConsumerConfig？你应该使用 :

import org.apache.kafka.clients.consumer.KafkaConsumer;
import org.apache.kafka.clients.consumer.ConsumerRecords;
import org.apache.kafka.clients.consumer.ConsumerRecord;

KafkaConsumer<String, String> consumer = new KafkaConsumer
         <String, String>(props);

Why does Kafka consumer throw "java.lang.NoClassDefFoundError: kafka/consumer/ConsumerConfig" at startup?

Why does Kafka consumer throw "java.lang.NoClassDefFoundError: kafka/consumer/ConsumerConfig" at startup?

java

scala

maven

apache-kafka