JAVAlang.ClassCastException:class model-在主题中将JSON对象作为消息发送时，springboot kafka集成中出错

Question

我是Kafka新手，mymodel类用户[请求处理失败；嵌套异常为org.apache.Kafka.common.errors.SerializationException:无法将class model.User的值转换为value.serializer中指定的类org.apache.Kafka.common.serialization.StringSerializer]，根本原因是java。ClassCastException：类模型。无法将用户强制转换为java类。org上的lang.String（model.User位于加载器“app”的未命名模块中；java.lang.String位于加载器“bootstrap”的java.base模块中）。阿帕奇。Kafka。常见的序列化。字符串序列化程序。序列化（StringSerializer.java:28）~[kafka-clients-2.7.1.jar:na]at*

我怀疑这是由于Kafka配置中错误导入了StringSerializer和JSONSerializer。下面是我的代码

1-Kafka形象

package config;

import java.util.HashMap;
import java.util.Map;

import org.apache.kafka.clients.producer.ProducerConfig;
import org.apache.kafka.connect.json.JsonSerializer;
import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.Configuration;
import org.springframework.kafka.core.DefaultKafkaProducerFactory;
import org.springframework.kafka.core.KafkaTemplate;
import org.springframework.kafka.core.ProducerFactory;

import com.fasterxml.jackson.databind.ser.std.StringSerializer;

import model.User;

@Configuration
public class KafkaConfiguration {
    
    @Bean
    public ProducerFactory<String,User> producerFactory()
    {
        Map<String,Object> config=new HashMap<>();
        
        config.put(ProducerConfig.BOOTSTRAP_SERVERS_CONFIG,"127.0.0.1:9092");
        config.put(ProducerConfig.KEY_SERIALIZER_CLASS_CONFIG,StringSerializer.class);
        config.put(ProducerConfig.VALUE_SERIALIZER_CLASS_CONFIG,JsonSerializer.class);
        return new DefaultKafkaProducerFactory<>(config);
    }
    
    @Bean
    public KafkaTemplate<String,User> kafkaTemplate()
    {
        return new KafkaTemplate<>(producerFactory());
    }

}

2用户资源类

package com.example.demo;

import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.kafka.core.KafkaTemplate;
import org.springframework.web.bind.annotation.GetMapping;
import org.springframework.web.bind.annotation.PathVariable;
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.RestController;

import model.User;

@RestController
@RequestMapping("kafka")
public class UserResource {

    @Autowired
    KafkaTemplate<String,User> kafkatemplate;
    public static final String TOPIC="Kafka_Example";

    
    @GetMapping("/publish/{name}")
    public String postMessage(@PathVariable("name") final String name)
    {
        
    kafkatemplate.send(TOPIC,new User(name,"Technology",12000L));
    
    return "Published successfully";
    }
}

3-用户类

package model;

public class User {

    private String name;
    private String dept;
    private long salary;
    
    
    public User(String name, String dept, long salary) {
        super();
        this.name = name;
        this.dept = dept;
        this.salary = salary;
    }
    

    public String getName() {
        return name;
    }
    public void setName(String name) {
        this.name = name;
    }
    public String getDept() {
        return dept;
    }
    public void setDept(String dept) {
        this.dept = dept;
    }
    public long getSalary() {
        return salary;
    }
    public void setSalary(long salary) {
        this.salary = salary;
    }
    
    
    
}

谁能告诉我哪里出了问题？是否与进口有关（如果是，正确的是什么）？

谢啦

Answer 1

你的代码正确，但你导入错误StringSerializer使用下面导入

org.apache.kafka.common.serialization.StringSerializer
org.springframework.kafka.support.serializer.JsonSerializer

Answer 2

解决方案

1. 你需要用这个类导入字符串序列化器和json序列化器

 org.apache.kafka.common.serialization.StringSerializer
 org.springframework.kafka.support.serializer.JsonSerializer

我跟着这两件事，问题已经解决了