java - maven打包后如何运行jar

Question

我是 Java 新手，我想用 Java 编写一个简单的 Kafka 消费者应用程序。

pom.xml：

<project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
  xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/maven-v4_0_0.xsd">
  <modelVersion>4.0.0</modelVersion>
  <groupId>org.zhihu</groupId>
  <artifactId>kafka-consumer</artifactId>
  <packaging>jar</packaging>
  <version>1.0-SNAPSHOT</version>
  <name>kafkadev</name>
  <url>http://maven.apache.org</url>
  <repositories>
    <repository>
      <!-- Proper URL for Cloudera maven artifactory -->
      <id>cloudera</id>
      <url>https://repository.cloudera.com/artifactory/cloudera-repos/</url>
    </repository>
  </repositories>
  <dependencies>
    <dependency>
      <groupId>org.apache.kafka</groupId>
      <artifactId>kafka-clients</artifactId>
      <version>2.1.0</version>
      <scope>compile</scope>
  </dependency>
  <!-- gson -->
  <dependency>
      <groupId>com.google.code.gson</groupId>
      <artifactId>gson</artifactId>
      <version>2.8.2</version>
  </dependency>     
  <dependency>
      <groupId>org.elasticsearch</groupId>
      <artifactId>elasticsearch</artifactId>
      <version>5.6.12</version>
  </dependency>
  <dependency>
      <groupId>junit</groupId>
      <artifactId>junit</artifactId>
      <version>3.8.1</version>
      <scope>test</scope>
  </dependency>
    </dependencies>
    <build>
        <plugins>
      <plugin>
        <groupId>org.apache.maven.plugins</groupId>
        <artifactId>maven-compiler-plugin</artifactId>
        <version>3.7.0</version>
        <configuration>
          <source>1.8</source>
          <target>1.8</target>
        </configuration>
      </plugin>
    </plugins>
  </build>
</project>

java源代码：

package zhihu;
import java.util.Arrays;
import java.util.Base64;
import java.util.Properties;
import java.io.UnsupportedEncodingException;
import org.apache.kafka.clients.consumer.ConsumerConfig;
import org.apache.kafka.clients.consumer.ConsumerRecord;
import org.apache.kafka.clients.consumer.ConsumerRecords;
import org.apache.kafka.clients.consumer.KafkaConsumer;
import com.google.gson.Gson;


public class ZhihuCommentConsumer {
    public static void main(String[] args) throws InterruptedException, UnsupportedEncodingException {
        Properties properties = new Properties();
        properties.put("bootstrap.servers", "device1:9092,device2:9092");
        properties.put("kafka.topic", "zhihu_comment");
        properties.put("group.id", "test");
        runMainLoop(args, properties);
    }

    static void runMainLoop(String[] args, Properties properties) throws InterruptedException, UnsupportedEncodingException {

        // Create Kafka producer
        KafkaConsumer<String, String> consumer = new KafkaConsumer<String, String>(properties);

        try {   
        consumer.subscribe(Arrays.asList(properties.getProperty("kafka.topic")));           
        System.out.println("Subscribed to topic " + properties.getProperty("kafka.topic")); 

        while (true) 
        {
            ConsumerRecords<String, String> records = consumer.poll(100);
                for (ConsumerRecord<String, String> record : records) {
                    System.out.printf("partition = %s, offset = %d, key = %s, value = %s\n", record.partition(), record.offset(), record.key(), record.value() );
                }               
        }
        }

    finally {
        consumer.close();
        }
    }

}

这是层次结构：

├── pom.xml
├── src
│   └── main
│       └── java
│           └── zhihu
│               └── ZhihuCommentConsumer.java
└── target
    ├── classes
    │   └── zhihu
    │       └── ZhihuCommentConsumer.class

问题是：

我运行mvn package在目标目录中生成jar文件，然后执行java -cp target/kafka-consumer-1.0-SNAPSHOT.jar zhihu.ZhihuCommentConsumer（我不确定这是否正确）。

但是，事实证明：

Exception in thread "main" java.lang.NoClassDefFoundError: org/apache/kafka/clients/consumer/KafkaConsumer
        at zhihu.ZhihuCommentConsumer.runMainLoop(ZhihuCommentConsumer.java:33)
        at zhihu.ZhihuCommentConsumer.main(ZhihuCommentConsumer.java:27)
Caused by: java.lang.ClassNotFoundException: org.apache.kafka.clients.consumer.KafkaConsumer
        at java.net.URLClassLoader.findClass(URLClassLoader.java:381)
        at java.lang.ClassLoader.loadClass(ClassLoader.java:424)
        at sun.misc.Launcher$AppClassLoader.loadClass(Launcher.java:331)
        at java.lang.ClassLoader.loadClass(ClassLoader.java:357)
        ... 2 more

我检查了 maven 存储库.m2，已经下载了 kafka-client 包。我应该怎么做才能以正确的方式运行应用程序？

非常感谢，我将不胜感激。

标签： javamavenapache-kafkajar