Spring test/production application context

Question

Why when running spring tests with @ContextConfiguration(...) @Autowired works automatically and when running Java application I get NullPointerException?

With following example I get NullPointerException:

   public class FinalTest {

    @Autowired
    private App app;

    public FinalTest() {
    }

    public App getApp() {
        return app;
    }

    public void setApp(App app) {
        this.app = app;
    }

    public static void main(String[] args) {

        ApplicationContext context = new ClassPathXmlApplicationContext("applicationContext.xml");

        FinalTest finalTest = new FinalTest();
        finalTest.getApp().getCar().print();
        finalTest.getApp().getCar().getWheel().print();
    }
}

With following example it works:

public class FinalTest {

    private App app;

    public FinalTest() {
    }

    public App getApp() {
        return app;
    }

    public void setApp(App app) {
        this.app = app;
    }

    public static void main(String[] args) {

        ApplicationContext context = new ClassPathXmlApplicationContext("applicationContext.xml");

        FinalTest finalTest = new FinalTest();
        finalTest.setApp((App)context.getBean("app"));
        finalTest.getApp().getCar().print();
        finalTest.getApp().getCar().getWheel().print();
    }
}

In tests no need of doing context.getBean(), it just works with @Autowired:

@RunWith(SpringJUnit4ClassRunner.class)
@ContextConfiguration(locations={"/applicationContext-test.xml"})
public class AppTest{

    @Autowired
    private App app;

    @Test
    public void test(){

        assertEquals("This is a SEAT_test car.", this.app.getCar().toString());
        assertEquals("This is a 10_test wheel.", this.app.getCar().getWheel().toString());
    }
}

Thanks.

Answer 1

Anytime you use @Autowired , the class into which the dependency is going to be injected needs to be managed by Spring.

A test with:

@RunWith(SpringJUnit4ClassRunner.class)
@ContextConfiguration(locations={"/applicationContext-test.xml"})

is managed by Spring. When the annotations do not exist, the class is not managed by Spring and therefor no dependency injection is performed

Answer 2

You're expecting Spring to be able to inject beans into an instance it doesn't manage.

You're creating your object manually

FinalTest finalTest = new FinalTest();

Spring can only inject beans into objects it manages. Here, Spring has nothing to do with the object created above.

Declare a FinalTest bean in your context and retrieve it. It will have been autowired if your configuration is correct.