Guice inject based on annotation value

Question

I would like to use goolge/guice inject a value based on a class i provide with the annotation.

AutoConfig annotation

@BindingAnnotation
@Retention(R         


        

Answer 1

I had a similar problem. I wanted to use a custom annotation that receives a enum param to choose the implementation. After a lot of research, debug and testing, I came to the following solution:

//enum to define authentication types
public enum AuthType {
    Ldap, Saml
}

//custom annotation to be used in injection
@Target({ ElementType.FIELD, ElementType.PARAMETER, ElementType.METHOD })
@BindingAnnotation
public @interface Auth {
    AuthType value();
}

//defintion of authenticator
public interface Authenticator {
    public void doSomehting();
}


//Authenticator implementations 
public class LdapAuthenticator implements Authenticator {

    @Override
    public void doSomehting() {
        // doing ldap stuff
    }

}

public class SamlAuthenticator implements Authenticator {

    @Override
    public void doSomehting() {
        // doing saml stuff
    }

}

public class MyModule extends AbstractModule {

    // annotate fields to bind to implementations
    private @Auth(AuthType.Ldap) Authenticator ldap;
    private @Auth(AuthType.Saml) Authenticator saml;

    @Override
    protected void configure() {
        //bind the implementation to the annotation from field
        bindAnnotated("ldap", LdapAuthenticator.class);
        bindAnnotated("saml", SamlAuthenticator.class);

    }

    private void bindAnnotated(String fieldName, Class implementation) {
        try {
            //get the annotation from fields, then bind it to implementation                
            Annotation ann = MyModule.class.getDeclaredField(fieldName).getAnnotation(Auth.class);
            bind(Authenticator.class).annotatedWith(ann).to(implementation);
        } catch (NoSuchFieldException | SecurityException e) {
            throw new RuntimeException(e);
        }
    }
}


//usage:  add @Auth() to the dependency

public class ClientClass {

    private Authenticator authenticator;

    @Inject
    public ClientClass(@Auth(AuthType.Ldap) Authenticator authenticator) {
        this.authenticator = authenticator;
    }
}

Check the documentation of Binder

I tested the Jeff Bowman solution, but it apparently works only binding to providers