如何在Maven项目中将依赖项org.apache.kafka.clients.producer.Producer解析为apache kafka的Java生产者

Question

This is the controller for my java web application. package com.proj.controller;

import org.springframework.web.bind.annotation.RequestBody;
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.RequestMethod;
import org.springframework.web.bind.annotation.ResponseBody;
import org.springframework.web.bind.annotation.RestController;

import com.proj.dao.Kafka_ObjectDao;
import com.proj.daoImpl.Kafka_ObjectDaoImpl;
import com.proj.model.Kafka_Object;

@RestController
public class MainController {

Kafka_ObjectDao kafka_ObjectDao = new Kafka_ObjectDaoImpl();

@RequestMapping("/")
public String welcome() {

    return "<h1>Welcome to Rest Services for Kafka</h1><br><br>";
}

 @RequestMapping(value = "/modify/student", method = RequestMethod.POST)
  public @ResponseBody int modifyStudent(@RequestBody Kafka_Object kafka_Object)
 { 
     System.out.println("In controller"); 
     return kafka_ObjectDao.modifyStudent(kafka_Object);

  } 
}

The Dao for this web application is package com.proj.dao;

   import com.proj.model.Kafka_Object;

 public interface Kafka_ObjectDao {

  public int modifyStudent(Kafka_Object kafka_Object);

}

The implementation for the dao interface is

    package com.proj.daoImpl;
import java.util.Properties;
import org.apache.kafka.clients.producer.KafkaProducer;
import org.apache.kafka.clients.producer.Producer;
import org.apache.kafka.clients.producer.ProducerRecord;

import com.google.gson.Gson;
import com.proj.dao.Kafka_ObjectDao;
import com.proj.model.Kafka_Object;

public class Kafka_ObjectDaoImpl implements Kafka_ObjectDao {
Gson gson = new Gson();

public Kafka_ObjectDaoImpl() {
}

public int modifyStudent(Kafka_Object pojo) {
    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", "org.apache.kafka.common.serialization.StringSerializer");
    props.put("value.serializer", "org.apache.kafka.common.serialization.StringSerializer");
    try {
        Producer<String, String> producer = new KafkaProducer<String, String>(props);
        ProducerRecord<String, String> PR = new ProducerRecord<String, String>("test", gson.toJson(pojo));
        producer.send(PR);
        System.out.println("Sent:" + PR.toString());
        producer.close();
    } catch (Exception e) {
        e.printStackTrace();
    }
    return 1;
}

}

The application configuration for this web application is

    package com.proj.config;
import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.ComponentScan;
import org.springframework.context.annotation.Configuration;

import com.proj.dao.Kafka_ObjectDao;
import com.proj.daoImpl.Kafka_ObjectDaoImpl;

@Configuration
@ComponentScan(basePackages = "com.proj")
public class ApplicationConfig {

@Bean
public Kafka_ObjectDao getKafka_ObjectDao() {
    return new Kafka_ObjectDaoImpl();
}
}

The pom.xml for my maven project is

    <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>com.rest</groupId>
<artifactId>QIC_FIRST</artifactId>
<packaging>war</packaging>
<version>1.0-SNAPSHOT</version>
<name>QIC_FIRST Maven Webapp</name>
<url>http://maven.apache.org</url>
<dependencies>
    <dependency>
        <groupId>junit</groupId>
        <artifactId>junit</artifactId>
        <version>3.8.1</version>
        <scope>test</scope>
    </dependency>
    <dependency>
        <groupId>org.apache.kafka</groupId>
        <artifactId>kafka-clients</artifactId>
        <version>0.9.0.1</version>
        <scope>provided</scope>
    </dependency>
    <dependency>
        <groupId>org.apache.kafka</groupId>
        <artifactId>kafka_2.10</artifactId>
        <version>0.10.0.0</version>
    </dependency>
    <dependency>
        <groupId>com.google.code.gson</groupId>
        <artifactId>gson</artifactId>
        <version>2.6.2</version>
    </dependency>
    <dependency>
        <groupId>org.springframework.data</groupId>
        <artifactId>spring-data-rest-webmvc</artifactId>
        <version>2.4.2.RELEASE</version>
    </dependency>
    <dependency>
        <groupId>javax.servlet</groupId>
        <artifactId>javax.servlet-api</artifactId>
        <version>3.1.0</version>
    </dependency>
    <dependency>
        <groupId>org.springframework</groupId>
        <artifactId>spring-jdbc</artifactId>
        <version>4.3.0.RELEASE</version>
    </dependency>
    <dependency>
        <groupId>com.google.code.gson</groupId>
        <artifactId>gson</artifactId>
        <version>2.6.2</version>
    </dependency>
</dependencies>
<build>
    <finalName>QIC_FIRST</finalName>
</build>
</project>

The error what am getting is

  Caused by: java.lang.ClassNotFoundException:org.apache.kafka.clients.producer.Producer

The complete error list is

    SEVERE: Exception sending context initialized event to listener instance       of class org.springframework.web.context.ContextLoaderListener
  org.springframework.beans.factory.BeanCreationException: Error creating bean with name 'mainController' defined in file            [C:\Users\teja.k\workspace\.metadata\.plugins\org.eclipse.wst.server.core\tmp2\wtpwebapps\QIC_FIRST\WEB-INF\classes\com\proj\controller\MainController.class]: Instantiation of bean failed; nested exception is org.springframework.beans.BeanInstantiationException: Failed to instantiate [com.proj.controller.MainController]: Constructor threw exception; nested exception is java.lang.NoClassDefFoundError: org/apache/kafka/clients/producer/Producer
at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.instantiateBean(AbstractAutowireCapableBeanFactory.java:1105)
at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.createBeanInstance(AbstractAutowireCapableBeanFactory.java:1050)
at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.doCreateBean(AbstractAutowireCapableBeanFactory.java:510)
at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.createBean(AbstractAutowireCapableBeanFactory.java:482)
at org.springframework.beans.factory.support.AbstractBeanFactory$1.getObject(AbstractBeanFactory.java:306)
at org.springframework.beans.factory.support.DefaultSingletonBeanRegistry.getSingleton(DefaultSingletonBeanRegistry.java:230)
at org.springframework.beans.factory.support.AbstractBeanFactory.doGetBean(AbstractBeanFactory.java:302)
at org.springframework.beans.factory.support.AbstractBeanFactory.getBean(AbstractBeanFactory.java:197)
at org.springframework.beans.factory.support.DefaultListableBeanFactory.preInstantiateSingletons(DefaultListableBeanFactory.java:775)
at org.springframework.context.support.AbstractApplicationContext.finishBeanFactoryInitialization(AbstractApplicationContext.java:762)
at org.springframework.context.support.AbstractApplicationContext.refresh(AbstractApplicationContext.java:480)
at org.springframework.web.context.ContextLoader.configureAndRefreshWebApplicationContext(ContextLoader.java:434)
at org.springframework.web.context.ContextLoader.initWebApplicationContext(ContextLoader.java:306)
at org.springframework.web.context.ContextLoaderListener.contextInitialized(ContextLoaderListener.java:106)
at org.apache.catalina.core.StandardContext.listenerStart(StandardContext.java:5097)
at org.apache.catalina.core.StandardContext.startInternal(StandardContext.java:5615)
at org.apache.catalina.util.LifecycleBase.start(LifecycleBase.java:147)
at org.apache.catalina.core.ContainerBase$StartChild.call(ContainerBase.java:1571)
at org.apache.catalina.core.ContainerBase$StartChild.call(ContainerBase.java:1561)
at java.util.concurrent.FutureTask.run(FutureTask.java:266)
at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1142)
at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:617)
at java.lang.Thread.run(Thread.java:745)
  Caused by: org.springframework.beans.BeanInstantiationException: Failed to instantiate [com.proj.controller.MainController]: Constructor threw exception; nested exception is java.lang.NoClassDefFoundError: org/apache/kafka/clients/producer/Producer
at org.springframework.beans.BeanUtils.instantiateClass(BeanUtils.java:159)
at org.springframework.beans.factory.support.SimpleInstantiationStrategy.instantiate(SimpleInstantiationStrategy.java:89)
at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.instantiateBean(AbstractAutowireCapableBeanFactory.java:1098)
... 22 more
Caused by: java.lang.NoClassDefFoundError: org/apache/kafka/clients/producer/Producer
at com.proj.controller.MainController.<init>(MainController.java:16)
at sun.reflect.NativeConstructorAccessorImpl.newInstance0(Native Method)
at sun.reflect.NativeConstructorAccessorImpl.newInstance(NativeConstructorAccessorImpl.java:62)
at sun.reflect.DelegatingConstructorAccessorImpl.newInstance(DelegatingConstructorAccessorImpl.java:45)
at java.lang.reflect.Constructor.newInstance(Constructor.java:422)
at org.springframework.beans.BeanUtils.instantiateClass(BeanUtils.java:147)
... 24 more
  Caused by: java.lang.ClassNotFoundException: org.apache.kafka.clients.producer.Producer
at       org.apache.catalina.loader.WebappClassLoaderBase.loadClass(WebappClassLoaderBase  .java:1891)
at         org.apache.catalina.loader.WebappClassLoaderBase.loadClass(WebappClassLoaderBase.java:1734)
... 30 more

Thanks in advance.

Answer 1

Your kafka-clients dependency has a provided scope. It should be compile or runtime . A scope of provided will not put the dependency into the .jar file. If you use provided you have to manually add the .jar to your classpath by some other means. The easiest solution is to remove the <scope>provided</scope> from your kafka-clients dependency.