@Import vs @ContextConfiguration in Spring

Question

Is there any difference in usage of the annotations? Both the annotations allow to use multiple @Configuration classes to create an ApplicationContext. From their docs @ContextConfiguration seems to be more suitable for test configuration and comes from an artifact for tests (spring-test), however, I haven't found the actual difference.

Thank you for any thoughts!

Solution 1

@Import and @ContextConfiguration are for different use cases and cannot be used interchangeability.

The @Import is only useful for importing other @Configuration files and is only useful (and afaik) and functional on @Configuration classes. When putting the @Import on a test class it will be no good as it won't be processed.

@Configuration
@Import(PersistenceConfig.class)
public class MainConfig {}

Using @Import can be useful if for instance you have disabled component scanning for @Configuration classes or you need an @Configuration class from a package not covered by your component-scan.

Note: There is also @ImportResource which does the same for older XML based configuration files.

The reverse is valid for @ContextConfiguration as that is only useful on Spring based test classes (tests ran with the SpringRunner for jUnit 4). It is used to supply the test with the configuration parameters to make up the test configuration. It can be a collection of XML, javaconfig (or a combination thereof).

@RunWith(SpringRunner.class)
@ContextConfiguration( classes = {MainConfig.class, TestConfig.class})
public MyTest {}

It also allows to specify what to use to load those configuration (amongst others).

Solution 2

in Spring Boot @Import(SomeConfiguration.class) adds configuration class to existing context. It is useful with test slices:

@DataJpaTest
@Import(SomeConfiguration.class)
class TestSomething(){...}

Here you have access to repositories and your beans from SomeConfiguration class.

@ContextConfiguration(classes = SomeConfiguration.class) mean use only this configuration , which could not work with eg. DataJpaTest.

Comments

[M. Deinum]

@ContextConfiguration is only usable in tests in other code it doesn't do anything. @Import is useless on a test and will only be useful on @Configuration classes to import other configuration classes (with @ImportResource you can import XML configuration files).

[Dmitry Senkovich]

@M. Deinum hi, thanks! but what is the purpose of it then? I may use @Import - and this is it

[M. Deinum]

As stated to @Import (aka include, load etc) other java configuration classes. For instance those not covered by component scanning (or maybe you disabled component scanning for @Configuration files). Or to create a separate configuration for test which @Imports the original configuration so that you can override beans ...

[Dmitry Senkovich]

@M. Deinum ok, I got the first idea. but in the second I could simply put @Import on test class, why to use @ContextConfiguration here? sorry if I'm being stupid:)

[M. Deinum]

Because as I also already stated, @Import is only useful (and functional) on @Configuration classes. It won't do anything on a test class, the only thing it does is take up a line of code.

[Dmitry Senkovich]

@M. Deinum awesome, now I see. thank you very much!

[Torsten]

@Deinum - Wow thanks - I got the point it's just the other way around. But I have to disagree, using @Import(TestConfig.class) on my Test will import that Beans, if they are not defined in my AppConfig. Which is picked up by SpringBootTest. And that made me crazy - because if my AppConfig has that Bean defined, the Imported is ignored. Makes no sense. So don't do that.

[Dmitry Senkovich]

a note: ContextCongifuration can be used either with XML or Java configurations: > As of Spring 3.1, context loaders may choose to support either path-based or class-based resources.

[Sam Brannen]

Well... you can actually annotate a test class with @Import when using Spring Boot. ;-) docs.spring.io/spring-boot/docs/1.5.9.RELEASE/reference/…

[davidcyp]

@SamBrannen but does it behave exactly the same?