引用服务类内部的配置类时出现BeanCreationException错误

Question

    @Service
    public class ImageService {

        public static Logger logger = Logger.getLogger(ImageService.class.getName());

        @Autowired
        MyProperties prop;

        private final String FILE_UPLOAD_LOCATION = prop.getUploadFileLocation() +"uploads/images/";

        public void upload(String base64ImageFIle) throws IOException {
            logger.info(FILE_UPLOAD_LOCATION);
        }
    }

这是我的配置类

    @Data
    @Configuration
    @ConfigurationProperties (prefix = "my")
    public class MyProperties {

        private String resourceLocation;

        private String resourceUrl;

        public String getUploadFileLocation() {
            return getResourceLocation().replace("file:///", "");
        }

        public String getBaseResourceUrl() {
            return getResourceUrl().replace("**", "");
        }
    }

这里是我可以成功使用MyProperties的地方

    @Configuration
    public class StaticResourceConfiguration implements WebMvcConfigurer {

        @Autowired
        MyProperties prop;

        @Override
        public void addResourceHandlers(ResourceHandlerRegistry registry) {
            registry.addResourceHandler(prop.getResourceUrl())
                    .addResourceLocations(prop.getResourceLocation());
        }
    }

Answer 1

问题是您试图使用自动连线字段来设置内联字段分配中的值。

这意味着

private final String FILE_UPLOAD_LOCATION = prop.getUploadFileLocation() +"uploads/images/";

在prop自动连线之前执行，这意味着它将始终为空

@Service
public class ImageService {

    //Fine since you are using static method
    public static Logger logger = Logger.getLogger(ImageService.class.getName());

    //Not needed if you are only using it to set FILE_UPLOAD_LOCATION
    //Allows field to be final
    private final MyProperties prop;

    //Still final
    private final String FILE_UPLOAD_LOCATION;

    //No need for @Autowired since implicit on component constructors
    ImageService(MyProperties prop){

        //Again not needed if you aren't going to use anywhere else in the class
        this.prop = prop;

        FILE_UPLOAD_LOCATION = prop.getUploadFileLocation() +"uploads/images/";
    }

    public void upload(String base64ImageFIle) throws IOException {
        logger.info(FILE_UPLOAD_LOCATION);
    }
}