Get value from application.properties without Main application

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?

two possible solutions would be (1) If you have controll over the library which provides `AuthAdapter` add component scan for package in which the `AuthAdapter` resides and annotate the `AuthAdapter` with `@Component` annotation (2) create a class annotated with `@Configuration` and in that class create a method annotated with `@Bean` which returns an instance of `AuthAdapter` — , Mar 25 '19 at 16:20
Yes, i have the control of the entire library, 'cos i wrote it from scratch. Can you provide me a simple snippet, based on solution 1)? thank you anyway :) — Marco, Mar 25 '19 at 16:22
Possible duplicate of [How to read data from java properties file using Spring Boot](https://stackoverflow.com/questions/38281512/how-to-read-data-from-java-properties-file-using-spring-boot) — sam, Mar 25 '19 at 17:11

score 0 · Answer 1 · answered Mar 25 '19 at 16:21

0

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.

answered Mar 25 '19 at 16:21

Tech Guy

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as the `AuthAdapter` comes from a library, component scan should be added to tell spring boot to scan the package of `AuthAdapter` – Mar 25 '19 at 16:22

Ryuzaki L · Answer 2 · 2019-03-25T16:28:29.790

@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);

     }
}

Thank for your answer, i tried your second version (the @ComponentScan way) but the compiler says me that he could not resolve the placeholder. I answered my own question with the error code if you want to check it. — Marco, Mar 25 '19 at 16:39

score 0 · Answer 3 · answered Mar 25 '19 at 16:41

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

the property "signin.key" is not present in the application.properties
SpringBoot did not start => make sure that in your application there is a main annoted with @springbootapplication
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.

I think that the class is IAuthAdapter to autowire it. However i tried your version, but i still get the error i posted above. — Marco, Mar 25 '19 at 16:51

score 0 · Answer 4 · answered Mar 25 '19 at 16:44

0

Make sure that the "signin.key" is present in the application.properties and that the is present in the jar generated

answered Mar 25 '19 at 16:44

David ROSEY

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Get value from application.properties without Main application

4 Answers4