How to use Spring @Value annotation in class level variables

Question

I need to use injected parameter by @Value in instance variable of a class and can be reused that variable in all its child classes.

   @Value(server.environment)
   public String environment;

   public String fileName = environment + "SomeFileName.xls";

Here, the problem is fileName initializing first and then environment injection is happening. So I am getting always null-SomeFileName.xls.

Anyway to convey to initialize first @Value in spring.

Answer 1

You can use @PostConstruct therefore. From documentation:

The PostConstruct annotation is used on a method that needs to be executed after dependency injection is done to perform any initialization.

@PostConstruct allows you to perform modification after properties were set. One solution would be something like this:

public class MyService {

    @Value("${myProperty}")
    private String propertyValue;

    @PostConstruct
    public void init() {
        this.propertyValue += "/SomeFileName.xls";
    }

}

Another way would be using an @Autowired config-method. From documentation:

Marks a constructor, field, setter method or config method as to be autowired by Spring's dependency injection facilities.

...

Config methods may have an arbitrary name and any number of arguments; each of those arguments will be autowired with a matching bean in the Spring container. Bean property setter methods are effectively just a special case of such a general config method. Such config methods do not have to be public.

Example:

public class MyService {

    private String propertyValue;

    @Autowired
    public void initProperty(@Value("${myProperty}") String propertyValue) {
        this.propertyValue = propertyValue + "/SomeFileName.xls";
    }

}

The difference is that with the second approach you don't have an additional hook to your bean, you adapt it as it is being autowired.