I'm seeing some odd behavior, I was hoping someone here can shine some light on the issue.
Let me start by describing my setup. First, a simple data object
public class Apple {
private String name;
public Apple withName(String name) {
this.name = name;
return this;
}
public String getName() {
return name;
}
}
And a test class..
@RunWith(SpringJUnit4ClassRunner.class)
@ContextConfiguration(classes={TestConfig.class})
public class AppleTest {
@Autowired private Apple apples;
@Test
public void simpleTest() {
System.out.println("OBJ: "+apples);
}
}
The config is as follows
@Configuration
public interface ConfigInterface {
public Apple getApple();
}
With an implementing class
@Configuration
@Import(AbstractTestConfig.class)
public class TestConfig implements ConfigInterface {
public Apple getApple() {
return new Apple().withName("Granny apples");
}
}
With the config dependency...
@Configuration
public class AbstractTestConfig {
@Autowired ConfigInterface conf;
@Bean Apple myTestApple() {
return conf.getApple();
}
}
All of this works great. I run the test, I see the output I expect. But then I throw a spanner into the wheel and modify AbstractTestConfig to look as follows.
@Configuration
public class AbstractTestConfig {
@Autowired ConfigInterface conf;
@Bean Apple myTestApple() {
return conf.getApple();
}
// NEW CODE
@Bean CustomScopeConfigurer scopeConfigurer() {
return new CustomScopeConfigurer();
}
}
And all of a sudden the @Autowired
object conf
is null when it is required to construct the Apple
bean.
Even more odd, if I move the CustomScopeConfigurer
bean to the TestConfig
class, then it works.
Is there something I don't know about scopes or the CustomScopeConfigurer
object in particular?
Copied from Spring @Bean javadoc:
BeanFactoryPostProcessor-returning @Bean methods
Special consideration must be taken for @Bean methods that return Spring BeanFactoryPostProcessor (BFPP) types. Because BFPP objects must be instantiated very early in the container lifecycle, they can interfere with processing of annotations such as @Autowired, @Value, and @PostConstruct within @Configuration classes. To avoid these lifecycle issues, mark BFPP-returning @Bean methods as static. For example:
@Bean
public static PropertyPlaceholderConfigurer ppc() {
// instantiate, configure and return ppc ...
}
By marking this method as static, it can be invoked without causing instantiation of its declaring @Configuration class, thus avoiding the above-mentioned lifecycle conflicts. Note however that static @Bean methods will not be enhanced for scoping and AOP semantics as mentioned above. This works out in BFPP cases, as they are not typically referenced by other @Bean methods. As a reminder, a WARN-level log message will be issued for any non-static @Bean methods having a return type assignable to BeanFactoryPostProcessor.
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