BeanCreationException error when referencing configuration class inside a service class

I am trying to @Autowire a @Configuration class inside a @Service class. basically my @Configuration class contains mapping to my custom .properties file. When i try to autowire my configuration class inside my service class, BeanCreationException occurs. I am not sure what happen. Just followed the guide on creating Property classes from spring. There must be something i missed out.

Also, when i try to autowire @Configuration class to another @Configuration class, it runs smoothly

Currently, i know that, prop is always null because when i remove prop.getUploadFileLocation() call, everything will be fine. There must be something wrong during autowiring.

Here is my Service class

    @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);
    	}
    }

Here is my Configuration class

    @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("**", "");
    	}
    }

And here is where i can successfully use MyProperties

    @Configuration
    public class StaticResourceConfiguration implements WebMvcConfigurer {
    
    	@Autowired
    	MyProperties prop;
    	
    	@Override
    	public void addResourceHandlers(ResourceHandlerRegistry registry) {
    		registry.addResourceHandler(prop.getResourceUrl())
    				.addResourceLocations(prop.getResourceLocation());
    	}
    }

The issue is that you are trying to use an autowired field to set the value in an inline field assignment.

That means

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

is executed before the prop is autowired, meaning it will always be null

The way to mitigate this would be to use constructor injection instead.

@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);
    }
}

See this question for why constructor is preferred over @autowired in general

If you need MyProperties bean to be created before StaticResourceConfiguration bean, you can put @ConditionalOnBean(MyProperties.class) as following. Spring will make sure MyProperties is there before processing StaticResourceConfiguration.

@Configuration
@ConditionalOnBean(MyProperties.class)
public class StaticResourceConfiguration implements WebMvcConfigurer {