Not able to inject values in a field

Question

@Component
@PropertySources({ @PropertySource("classpath:mail.properties") })
public class A implements B {

@Value("${mail.team.address}")
    private String teamAddress;

// has getter and setters .not shown for brevity.

Now when i call the class i get the value of teamAddress as NULL .But in the property file mail.team.address has some value.

My property file is present under src/main/resource folder

Making a call

 A a = new A ();
  a.someMethodinClassA();

what do you mean Now when i call the class i get the value of teamAddress? — Sangam Belose, May 15 '18 at 11:22
i get the value as NULL.i expect some emaild address to be displayed.Whatever i have stored in the property file — Rahul, May 15 '18 at 11:24
mail.host=something mail.from= mail.team.address=abc@gmail.com — Rahul, May 15 '18 at 11:31
Possible duplicate of [Why is my Spring @Autowired field null?](https://stackoverflow.com/questions/19896870/why-is-my-spring-autowired-field-null) — Jesper, May 15 '18 at 11:37
The `new A()` is why it does not work. Things like `@Autowired` and `@Value` only work in Spring beans (objects created and managed by Spring) and not in objects you create yourself when you use `new`. — Jesper, May 15 '18 at 11:39
@Rahul in spring you should not create class object by yourself. the spring container create the same for you. that is also singletone (single object per container). check my answer around this — Sangam Belose, May 15 '18 at 11:58
ok how can i inject and call the method.This is a stand alone project .Not a web project — Rahul, May 15 '18 at 12:26

score 0 · Answer 1 · edited Jun 20 '20 at 09:12

You can not create instance of class by yourself when you want Spring to resolve @Value annotation.

See documentation:

Note that actual processing of the @Value annotation is performed by a BeanPostProcessor which in turn means that you cannot use @Value within BeanPostProcessor or BeanFactoryPostProcessor types. Please consult the javadoc for the AutowiredAnnotationBeanPostProcessor class (which, by default, checks for the presence of this annotation).

Simple solution for you: just annotate class with any @Component annotation and let Spring to create an instance of your class.

score 0 · Answer 2 · answered May 15 '18 at 11:44

You can't create (with a "new" keywoard) for spring bean. If you do it like this, spring doesn't participate in the object creation and configuration, which means that there is no autowiring, the bean is not in Application Context, etc. And of course, @Value annotation won't be processed among other things

The better way is to inject the class A to the code that you used in your example:

A a = new A ();
a.someMethodinClassA();

Show become:

@Component 
public class SomeClass {
   private final A a;
   public SomeClass(A a) {
      this.a = a;
   }

   public void foo() {
         a.someMethodinClassA();
   }

}

basically yes, but you don't do "new" by yourself, instead ask Spring to bring you a bean of type SomeClass. — Mark Bramnik, May 16 '18 at 21:41

score 0 · Answer 3 · answered May 15 '18 at 11:57

You should read some basics around spring dependency injection. The class that you have autowired with @Component is scanned via component scanning and its object is created by spring container for you.

that is the reason you should not create the object yourself using new keyword.

wherever in your new class you want to use your class A object you can autowire it as below:

@Component
public class TestC{

private A a; // this object will be injected by spring for you

}

Not able to inject values in a field

3 Answers3