从没有主应用程序的 application.properties 中获取价值

Question

I' m working in a Spring Boot project, consisted in several applications booted with embedded Tomcat and a unique application used only as library for running applications. In that library application I need to retrieve a value from application.properties file for a variable. Being it a library application, it has not a Main class, so the variable will be always null. My try was these:

 public class AuthAdapter implements IAuthAdapter {

    @Value("${signin.key}")
    private String key;

    @Override
    public String getSigningKey() {
        return key;
    }
}

When the getSigninKey() is invoked by an application that uses it, the variable key is null. How can I do to fill the variable key with the value present on appliaction.properties file, considering the situation explained before?

Answer 1

You need to annotate your AuthAdapter class with @Service/@Component/@Repository/@Configuration based on your requirement. By doing so, spring boot will inject the application.properties to your class during the spring context initialization.

Answer 2

@Value Spring annotation

This annotation can be used for injecting values into fields in Spring-managed beans

So make AuthAdapter as spring bean in some config class

@Configuration
public class ApplicationConfig {

 @Bean
 public AuthAdapter getAuthAdapter() {

  return new AuthAdapter():
  }
}

with property in application.yml or application.properties

application.yml

signin:
  key: value

Or if AuthAdapter is annotated with any stereotype annotations here , Just enable that class in ComponentScan

@SpringBootApplication
@ComponentScan({ "com.project1", "com.library.AuthAdapter" })
public class Main {

    public static void main(String[] args) {

        SpringApplication.run(Main.class);

     }
}

Answer 3

If the variable key==null, this means that Spring did not inject it. This could come from sevreral reasons:

1. the property "signin.key" is not present in the application.properties

2. SpringBoot did not start => make sure that in your application there is a main annoted with @springbootapplication

3. The AuthAdapter is not instanciate by Spring:

=> The AuthAdapter shall not be instanciate like:

authAdapter = new AuthAdapter();

Instead, it must be instanciate and injected by Spring itself like:

@Autowired
private authAdapter AuthAdapter;

For that the AuthAdapter must be annoted with a springBoot annotation: @Service/@Component/@Repository/@Configuration .

Finally, the package containing the AuthAdapter class must be in the component scan perimeter to tell Spring to instanciate it.

Answer 4

确保“signin.key”存在于 application.properties 中并且存在于生成的 jar 中