How to inject an object via annotation and set an attribute value on this object

Question

I am using the @Resource annotation to inject an object which is working fine. However I would like to set an attribute on this injected object and I'm not sure whether this is possible using annotations.

For example, I have class Test which has an instance of MyClass injected using the @Resource annotation. MyClass has an attribute, myAttribute , which I want to set when the MyClass instance is injected.

Does anyone know if this is possible?

Answer 1

You should make use of the @PostConstruct annotation, from javax.annotation :

public class Test {
    @Resource
    private MyClass myClass;

    @PostConstruct
    public void init() {
       myClass.setMyAttribute("test-class");
    }
}

public class AnotherTest {
    @Resource
    private MyClass myClass;

    @PostConstruct
    public void init() {
       myClass.setMyAttribute("another-test-class");
    }
}

This method will then be called after Spring has initialised your object (ie all dependencies have been injected).

I'm assuming that MyClass isn't a Singleton.

Answer 2

If you are sure that you won't have more than one dependency or alternative MyClass instances at runtime, you can use the solution by StuPointerException. But if both Test and AnotherTest exist in a single application context then due to the singleton default scope of spring beans the AnotherTest initialization will affect the state of Test as well.
This is because @Resource will inject the same bean into both owner beans.

To prevent this you should create different beans by the same class. This requires either xml configuration or JavaConfig. Since you favor annotations here it is:

@Configuration
public class AppConfig { 

    @Bean
    public MyClass myClass1() {
        MyClass myClass = new MyClass();
        myClass.setMyAttribute("attr-value-1");
        return myClass;
    }

    @Bean
    public MyClass myClass2() {
        MyClass myClass = new MyClass();
        myClass.setMyAttribute("attr-value-2");
        return myClass;
    }

}

And then you can autowire with @Resource as before but with different beans in each case

public class Test {
    @Resource("myClass1")
    private MyClass myClass;    
}

public class AnotherTest {
    @Resource("myClass2")
    private MyClass myClass;
}

Answer 3

DI with Spring :

@Autowired
MyClass myClass

With Java-ee :

@Inject
MyClass myClass

Concerning annotated property injection, you can still take a look at @Value , but you'll need a properties file along with it