如何通过接口映射器实现依赖关系

Question

我尝试使用java Spring映射对象DTO到对象正常

我尝试调用接口映射器，因为服务，但我有NullPointerExctive，似乎接口没有注入服务，我使用自动配置，我退出了这个

服务

@Service
public class FollowService implements IFollowService{

    @Autowired
    IFollowRepository iFollowRepository;

    private IUserMapper iUserMapper;

  @Override
    public UserDTOCount countFollowers(int userId) throws UserIdNotFoundException, UserNotFollowException {
        return iUserMapper.toUserCount(iFollowRepository.getUserById(userId));
    }

制图员

@Mapper(componentModel = "spring")
public interface IUserMapper {

  @Mappings({
          @Mapping(source = "id" , target = "id"),
          @Mapping(source = "name", target = "name"),
          @Mapping(source = "followers", target = "followers", qualifiedByName = "followers")
  })
  UserDTOCount toUserCount(User user);

错误

processing failed; nested exception is java.lang.NullPointerException] with root cause

java.lang.NullPointerException: null
    at com.reto1.demo.Service.FollowService.countFollowers(FollowService.java:54) ~[classes/:na]

我尝试调试，我看到iUserMapper是空的，我不知道如何调用，因为服务

谢谢！

Answer 1

看了很多问题后我用这个表格解决了错误

-首先，在pom中添加插件。xml

<build>
    <plugins>
        <plugin>
            <groupId>org.apache.maven.plugins</groupId>
            <artifactId>maven-compiler-plugin</artifactId>
            <version>3.8.1</version>
            <configuration>
                <source>1.8</source> <!-- depending on your project -->
                <target>1.8</target> <!-- depending on your project -->
                <annotationProcessorPaths>
                    <path>
                        <groupId>org.mapstruct</groupId>
                        <artifactId>mapstruct-processor</artifactId>
                        <version>${org.mapstruct.version}</version>
                    </path>
                    <!-- other annotation processors -->
                </annotationProcessorPaths>
            </configuration>
        </plugin>
    </plugins>
</build>

第二，我加入了龙目舞

 <annotationProcessorPaths>
                        <path>
                            <groupId>org.projectlombok</groupId>
                            <artifactId>lombok</artifactId>
                            <version>1.18.20</version>
                        </path>
                        <path>
                            <groupId>org.mapstruct</groupId>
                            <artifactId>mapstruct-processor</artifactId>
                            <version>1.4.1.Final</version>
                        </path>

最后我加上自动配发

@Service
public class FollowService implements IFollowService{

    @Autowired
    IFollowRepository iFollowRepository;

    @Autowired
    IUserMapper iUserMapper;

Answer 2

在FollowService中，iUserMapper为null的原因是您没有注射映射器。

您需要在服务中添加@Autowired。

e. g.

@Service
public class FollowService implements IFollowService{

    @Autowired
    IFollowRepository iFollowRepository;

    @Autowired
    private IUserMapper iUserMapper;

    @Override
    public UserDTOCount countFollowers(int userId) throws UserIdNotFoundException, UserNotFollowException {
        return iUserMapper.toUserCount(iFollowRepository.getUserById(userId));
    }

}

小评论：我的一个小离题。我建议不要在接口前面加I。IDE可以清楚地显示什么是类，什么是接口，而且在树结构中更容易看到它们，因为不是所有的东西都在“I”下