Spring 引导无法使用@Value 进行注入

Question

Spring Boot version <version>2.2.0.RELEASE</version>

Error goes as follows:

Description:

Parameter 2 of constructor in com.shawn.foodrating.service.impl.AdServiceImpl required a bean of type java.lang.Integer that could not be found.

Action:

Consider defining a bean of type 'java.lang.Integer' in your configuration.

My Code:

@Service
@Transactional(rollbackOn = Exception.class)
@AllArgsConstructor
public class AdServiceImpl implements AdService {
 private AdRepository repository;
 private FileService fileService;
 @Value("${app.ad.DefaultPageSize}")
 private Integer DEFAULT_PageSize;
 @Value("${app.ad.ImagePath}")
 private String AD_IMAGE_PATH;
 @Value("${app.ad.ImageUrl}")
 private String AD_IMAGE_URL;

Load property file

@SpringBootApplication
@PropertySource("classpath:app.properties")
public class FoodRatingApplication {
    public static void main(String[] args) {
        SpringApplication.run(FoodRatingApplication.class, args);
    }

}

Not Sure what is wrong with it.

Answer 1

When you use Lombok's @AllArgsConstructor it must create a constructor for all your fields, those annotated with @Value and those that aren't.

Now Lombok doesn't even know anything about @Value annotation of spring. So the generated constructor looks something like this:

public AdServiceImpl(AdRepository repository, FileService fileService, Integer DEFAULT_PageSize, String AD_IMAGE_PATH, String AD_IMAGE_URL) {
   this.repository = repository;
   ....
}

You can run Delombok to see the actually generated code.

Spring on the other hand when sees a single constuctor tries to call it to create the bean ( AdServiceImpl ) in this case, and only after that iterates through its fields and inject data annotated by @Value .

Now, when spring calls the constructor, it sees an integer (DEFAULT_PageSize), has no clue that its a value (and spring has to inject something brcause its a constructor injection), and throws an Exception.

So in terms of resolution:

Don't use all args constructor of lombok in this case and instead create a non-lombok constructor for AdRepository and FileService only)

Alternatively create a constructor with @Value annotated parameters instead of field injection (remove @Value on fields):

public AdServiceImpl(AdRepository repository, FileService fileService, @Value(${app.ad.DefaultPageSize}"} Integer DEFAULT_PageSize, @Value(...) String AD_IMAGE_PATH, @Value(...) String AD_IMAGE_URL) {
   this.repository = repository;
   ....
}

Answer 2

Add to projeck lombok.config file with this lines:

lombok.copyableAnnotations += org.springframework.beans.factory.annotation.Qualifier
lombok.copyableAnnotations += org.springframework.beans.factory.annotation.Value

Answer 3

The root cause is that you are using Lombok @AllArgsConstructor while some of the properties are populated by @Value(..) .

Replace the @AllArgsConstructor with @RequiredArgsConstructor and give it a try.

Note: Adding this comment for future references.

Answer 4

You can use in the following manner.

@Service
@Configuration
@ComponentScan
@PropertySource("classpath:app.properties")
@Transactional(rollbackOn = Exception.class)
@AllArgsConstructor
public class AdServiceImpl implements AdService {
 private AdRepository repository;
 private FileService fileService;
 @Value("${app.ad.DefaultPageSize}")
 private Integer DEFAULT_PageSize;
 @Value("${app.ad.ImagePath}")
 private String AD_IMAGE_PATH;
 @Value("${app.ad.ImageUrl}")
 private String AD_IMAGE_URL;

To use @Value annotation, you have to use @Configuration and @PropertySource in the same class.