How to forbid Spring Boot injecting both fields of the same type with the same bean instance?

Question

I have a class with two final fields of the same type, and I need to make second field injected with null if property props.enabled in application.yml is false. However, if it's false Spring Boot injects both fields with the same bean instance.

@AllArgsConstructor
public class MySettings {
    private int val;
}

My configuration class

@Configuration
public class MySpringConfig {

    @Bean
    public MySettings settingsA() { 
        return new MySettings(1);    
    } 
    
    @Bean
    @ConditionalOnProperty(prefix = "props", name = "enabled")
    public MySettings settingsB() {
        return new MySettings(2);
    }
}

And this is my class

@Component
@RequiredArgsConstructor
public class MyClass {
    
    private final MySettings settingsA; // MySettings(1)
    private final MySettings settingsB; // also MySettings(1) but must be null if props.enabled=false

    @Value("${props.enabled}")
    private boolean enabled;

    ...
}

This is part of the real project, so I have very little space to deviate from

UPDATE

I came up with solution of constructor injection but the code starts to look ugly

@Component
public class MyClass {

    private final MySettings settingsA;
    private final MySettings settingsB;

    private boolean enabled;

    public MyClass(MySettings settingsA, 
                   @Nullable @Qualifier("settingsB") MySettings settingsB, 
                   @Value("${props.enabled}") boolean enabled) {
        this.settingsA = settingsA;
        this.settingsB = settingsB;
        this.enabled = enabled;
    }
    ...

user_16572295 · Answer

You need a qualifier to tell Spring which bean to inject:

@Configuration
public class MySpringConfig {

    @Bean(name = "SettingsA")
    public MySettings settingsA() { 
        return new MySettings(1);    
    } 
    
    @Bean(name = "SettingsB")
    @ConditionalOnProperty(prefix = "props", name = "enabled")
    public MySettings settingsB() {
        return new MySettings(2);
    }
}

And now in MyClass:

@Component
public class MyClass {
    
    private final MySettings settingsA;
    private final MySettings settingsB;

    @Value("${props.enabled}")
    private boolean enabled;

    public MyClass(@Qualifier("SettingsA") MySettings settingsA, @Qualifier("SettingsB") MySettings settingsB) {
        this.settingsA = settingsA;
        this.settingsB = settingsB;
    }

    ...
}

However, since one of those Beans might not be available I believe you need to not include it in the constructor injection otherwise you will get an error. In that case you need to do the following:

@Component
public class MyClass {

    @Qualifier("SettingsA") 
    @Autowired
    private MySettings settingsA;

    @Qualifier("SettingsB")
    @Autowired(required = false)
    private MySettings settingsB;

    @Value("${props.enabled}")
    private boolean enabled;

    ...
}

How to forbid Spring Boot injecting both fields of the same type with the same bean instance?

1 Answers