Losing Spring @Value("${}") when instantiate class

Question

I'm using SpringBoot 2.1.3 (Embedded Tomcat) + Thymeleaf 3.0 + Java 8.

I have a simple class like this:

@Data
public class Machine {
   private Integer price;
   @Value("${settings.default}")
   private String settings;
}

And a simple application.properties:

settings.default=deafult

But when I instantiate the class anyway in the code:

Machine m = new Machine();
System.out.println(m.getSettings);

It returns null. Obviuosly if I do:

@Data
public class Machine {
   private Integer price;
   private String settings = "Default";
}

It works.. Or if I use that value inside a class method it works again. What's wrong? Can I do something like that?

Thank you

Answer 1

A class should be declared with stereotype annotations to use @Value

@Component
public class Machine {
   private Integer price;
   @Value("${settings.default}")  
   private String settings;
}

And of course you have to autowire the Machine class (Spring has defined the bean), instantiating a new Object will not get the value, so to use

@Service
public class FooService {
  @Autowire
  private Machine machine;

  public void fooMethod() {
    System.out.println(machine.getSettings()); // default
  }
}