Spring Boot项目CurrencyExchangeRepository Bean注入失败问题求助

问题场景 #

启动Spring Boot项目时失败，报错信息如下：

应用启动失败
描述：
com.hb.CurrencyExchangeSampleController中的字段repo需要类型为'com.hb.CurrencyExchangeRepository'的Bean，但未找到。
注入点带有以下注解：

• @org.springframework.beans.factory.annotation.Autowired(required=true)
  操作建议：
  考虑在配置中定义类型为'com.hb.CurrencyExchangeRepository'的Bean。
  进程已断开与目标VM的连接，地址：'127.0.0.1:53276'，传输：'socket'
  进程退出码为0

用户提供的代码如下：

CurrencyExchangeRepository.java #

package com.hb;

import org.springframework.data.jpa.repository.JpaRepository;
import org.springframework.data.jpa.repository.Query;
import org.springframework.data.jpa.repository.config.EnableJpaRepositories;
import org.springframework.stereotype.Repository;

@Repository
@EnableJpaRepositories
public interface CurrencyExchangeRepository extends JpaRepository<CurrencyConversion, Long> {

    @Query("SELECT value FROM currency_conversion t WHERE t.from_country = ?1 and t.to_country = ?2")
    CurrencyConversion getCurrencyValue(String fromCurrency, String toCurrency);
}

CurrencyExchangeSampleController.java #

package com.hb;

import java.math.BigDecimal;

import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.beans.factory.annotation.Value;
import org.springframework.cloud.context.config.annotation.RefreshScope;
import org.springframework.web.bind.annotation.GetMapping;
import org.springframework.web.bind.annotation.PathVariable;
import org.springframework.web.bind.annotation.RestController;

@RefreshScope
@RestController
public class CurrencyExchangeSampleController {

    @Autowired
    CurrencyExchangeRepository repo;

    
    @GetMapping("/chenna")
    public String msg(){
        return "hello chenna";
    }

    @GetMapping("/currency-exchange-service/fromCurrency/{fromCurrency}/toCurrency/{toCurrency}")
    public ExchangeValue retrieveExchangeValue(@PathVariable String fromCurrency,
                                               @PathVariable String toCurrency) {

        System.out.println("msg : " + msg);
        CurrencyConversion cc = impl.getCurrencyValue(fromCurrency, toCurrency);
        System.out.println("value : " + cc.getValue());
    }
}

CurrencyExchangeServiceSampleApplication.java #

package com.hb;
@SpringBootApplication
@EnableDiscoveryClient
@EnableAutoConfiguration(exclude={DataSourceAutoConfiguration.class})
@ComponentScan("com.hb")
public class CurrencyExchangeServiceSampleApplication {

    public static void main(String[] args)
    {
        SpringApplication.run(
                CurrencyExchangeServiceSampleApplication.class,
                args);
    }
}

问题原因与解决办法 #

1. 禁用DataSource自动配置导致JPA Repository无法实例化 #

启动类中添加了@EnableAutoConfiguration(exclude={DataSourceAutoConfiguration.class})，直接禁用了Spring Boot的数据源自动配置。而JPA Repository的创建必须依赖数据源，没有数据源的情况下Spring无法生成CurrencyExchangeRepository的Bean实例。

解决：

• 如果项目需要使用JPA操作数据库，移除@EnableAutoConfiguration(exclude={DataSourceAutoConfiguration.class})；
• 在application.properties/application.yml中配置数据库连接信息，示例：

spring.datasource.url=jdbc:mysql://localhost:3306/your_database
spring.datasource.username=db_user
spring.datasource.password=db_password
spring.jpa.hibernate.ddl-auto=update
spring.jpa.show-sql=true

2. @EnableJpaRepositories注解位置错误 #

该注解被错误地添加在Repository接口上，它的正确位置是启动类，用来指定Spring扫描Repository接口的包路径。

解决：

• 移除CurrencyExchangeRepository接口上的@EnableJpaRepositories注解；
• 在启动类CurrencyExchangeServiceSampleApplication上添加@EnableJpaRepositories(basePackages = "com.hb")，确保Spring能扫描到Repository接口。

3. 其他潜在问题修正 #

• Repository查询语句错误：getCurrencyValue方法的@Query只查询value字段，但返回类型是CurrencyConversion实体，会导致查询报错，修改为查询整个实体：

@Query("SELECT t FROM CurrencyConversion t WHERE t.from_country = ?1 and t.to_country = ?2")
CurrencyConversion getCurrencyValue(String fromCurrency, String toCurrency);

• Controller方法错误：retrieveExchangeValue中使用了未定义的impl变量，应改为repo.getCurrencyValue；同时方法缺少返回值，需补充返回逻辑。

修正后的启动类示例 #

package com.hb;

import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;
import org.springframework.cloud.client.discovery.EnableDiscoveryClient;
import org.springframework.data.jpa.repository.config.EnableJpaRepositories;

@SpringBootApplication
@EnableDiscoveryClient
@EnableJpaRepositories(basePackages = "com.hb")
public class CurrencyExchangeServiceSampleApplication {

    public static void main(String[] args) {
        SpringApplication.run(CurrencyExchangeServiceSampleApplication.class, args);
    }
}

内容的提问来源于stack exchange，提问作者user18665270