Spring Boot中Mapper无法被Autowired注入的问题排查

问题场景 #

开发博彩API时，使用MapStruct的BetMapper减少DTO与实体类之间的转换代码重复，但遇到以下问题：

• 项目启动失败，提示找不到BetMapper类型的Bean
• 移除@Autowired注解后项目能启动，但调用投注插入接口时出现betMapper为null的空指针异常

启动报错信息 #

***************************
APPLICATION FAILED TO START
***************************

Description:

Parameter 1 of constructor in api.loteria.loteriaapi.services.Mysql.BetServiceMysql required a bean of type 'api.loteria.loteriaapi.dtos.mappers.BetMapper' that could not be found.

The injection point has the following annotations:
        - @org.springframework.beans.factory.annotation.Autowired(required=true)


Action:

Consider defining a bean of type 'api.loteria.loteriaapi.dtos.mappers.BetMapper' in your configuration.

相关代码 #

BetMapper.java #

@Mapper(componentModel = "spring")
public interface BetMapper {
    @Mapping(target = "bet.id", source = "betId")
    Bet betResquetToEntity(BetRequest betRequest);

    @Mapping(source = "bet.id", target = "betId")
    BetResponse entityToBetResponse(Bet bet);
}

BetServiceMysql.java #

@Service
@AllArgsConstructor(onConstructor = @__(@Autowired))
public class BetServiceMysql implements BetService {

    private BetRepository betRepository;
    private BetMapper betMapper;

    @Override
    public List<BetResponse> list() {
        List<Bet> bets = betRepository.findAll();
        return bets.stream().map(bet -> betMapper.entityToBetResponse(bet)).collect(Collectors.toList());
    }

    @Override
    public BetResponse save(BetRequest betRequest) {
        Bet bet = betMapper.betResquetToEntity(betRequest);
        try {
            betRepository.save(bet);
        }catch(RuntimeException e){
            throw new DataIntegrityViolationException(e.getMessage());
        }
        return betMapper.entityToBetResponse(bet);
    }

    @Override
    public BetResponse update(Long id, BetRequest betRequest) {
        Bet bet = verifyIfExist(id);
        updateData(bet, betRequest);
        betRepository.save(bet);
        return betMapper.entityToBetResponse(bet);
    }

    @Override
    public BetResponse delete(Long id) {
        Bet bet = verifyIfExist(id);
        betRepository.delete(bet);
        return betMapper.entityToBetResponse(bet);
    }

    @Override
    public BetResponse getBetById(Long id) {
        // TODO Auto-generated method stub
        return null;
    }

    @Override
    public List<BetResponse> getBets() {
        // TODO Auto-generated method stub
        return null;
    }

    protected Bet verifyIfExist(Long id){
        return betRepository.findById(id).orElseThrow(() -> new EntityNotFoundException(String.format("ID: %s || Não foi encontrado nenhuma entidade para o id fornecido", id)));
    }

    protected void updateData(Bet bet, BetRequest betRequest){
        bet.setMaxNumbersByUsers(betRequest.getMaxNumbersByUsers());
    }

}

BetService.java #

public interface BetService {
    List<BetResponse> list();
    BetResponse save(BetRequest betRequest);
    BetResponse update(Long id, BetRequest betRequest);
    BetResponse delete(Long id);
    BetResponse getBetById(Long id);
    List<BetResponse> getBets();
}

解决方案 #

1. 确保MapStruct依赖及注解处理器配置正确 #

MapStruct需要核心依赖和注解处理器才能生成Mapper的实现类，以Maven为例，在pom.xml中添加：

<!-- MapStruct核心依赖 -->
<dependency>
    <groupId>org.mapstruct</groupId>
    <artifactId>mapstruct</artifactId>
    <version>1.5.5.Final</version>
</dependency>
<!-- 注解处理器，用于编译时生成Mapper实现类 -->
<dependency>
    <groupId>org.mapstruct</groupId>
    <artifactId>mapstruct-processor</artifactId>
    <version>1.5.5.Final</version>
    <scope>provided</scope>
</dependency>

如果使用Gradle，需配置annotationProcessor：

dependencies {
    implementation 'org.mapstruct:mapstruct:1.5.5.Final'
    annotationProcessor 'org.mapstruct:mapstruct-processor:1.5.5.Final'
}

2. 确认Spring能扫描到Mapper接口 #

• 检查Spring Boot主类的@SpringBootApplication或@ComponentScan注解，确保Mapper所在的包api.loteria.loteriaapi.dtos.mappers被包含在扫描范围内：

@SpringBootApplication(scanBasePackages = {"api.loteria.loteriaapi"})
public class LoteriaApiApplication {
    public static void main(String[] args) {
        SpringApplication.run(LoteriaApiApplication.class, args);
    }
}

• @Mapper(componentModel = "spring")注解会让MapStruct生成带有@Component的实现类，确保Spring能自动扫描并注册为Bean。

3. 优化Service的依赖注入方式 #

替换@AllArgsConstructor(onConstructor = @__(@Autowired))为更简洁的构造注入方式，推荐使用Lombok的@RequiredArgsConstructor（需确保字段为private final）：

@Service
@RequiredArgsConstructor
public class BetServiceMysql implements BetService {

    private final BetRepository betRepository;
    private final BetMapper betMapper;

    // 原有业务方法保持不变...
}

如果不使用Lombok，可手动编写构造函数：

@Service
public class BetServiceMysql implements BetService {

    private final BetRepository betRepository;
    private final BetMapper betMapper;

    public BetServiceMysql(BetRepository betRepository, BetMapper betMapper) {
        this.betRepository = betRepository;
        this.betMapper = betMapper;
    }

    // 原有业务方法保持不变...
}

4. 验证Mapper实现类是否生成 #

编译项目后，检查target/classes/api/loteria/loteriaapi/dtos/mappers/目录下是否存在BetMapperImpl.class文件。如果不存在，说明注解处理器未生效，需重新检查依赖配置，或执行mvn clean compile（Maven）/gradle clean compileJava（Gradle）重新编译。

总结 #

问题核心是MapStruct未生成有效的Spring Bean实现类，或Spring无法扫描到该Bean。通过完善依赖配置、确保组件扫描范围正确、优化注入方式，即可解决启动报错和Mapper为null的问题。

内容的提问来源于stack exchange，提问作者Wesquel