Spring java config extending an abstract configuration

Question

in our software we are using spring java config. We have a setup, where one configuration extends an abstract configuration. Please have a look at this testcase:


    import java.util.concurrent.atomic.AtomicInteger;
    import org.junit.Test;
    import org.springframework.context.annotation.AnnotationConfigApplicationContext;
    import org.springframework.context.annotation.Bean;
    import org.springframework.context.annotation.Configuration;

    public class SpringConfigTest {

      @Test
      public void test() {
        final AnnotationConfigApplicationContext ctx = new AnnotationConfigApplicationContext(MyConfig.class);
        ctx.getBeansOfType(AtomicInteger.class).entrySet().stream().forEach(
            b -> System.out.println(b.getKey() + " : " + b.getValue() + " (" + b.getValue().hashCode() + ")"));
      }

      @Configuration
      public static class MyConfig extends AbstractConfig {

        @Bean(name = "anotherName")
        public AtomicInteger myBean() {
          return new AtomicInteger(5);
        }
      }

      public static abstract class AbstractConfig {

        @Bean
        public AtomicInteger myBean() {
          return new AtomicInteger(10);
        }
      }
    }

The idea is, that MyConfig overwrites AbstractConfig and in the created ApplicationContext there is only one bean of type AtomicInteger under the name anotherName.

The results was:

anotherName : 5 (2109798150)
myBean : 5 (1074389766)

So it says, there are two beans (two instances - one for each name) - and even more surpring: the same method (MyConfig#myBean()) was used to create both of them.

This behaviour looks odd to us: We expected that spring would either respect the usual java way of inheritance and create only the bean from MyConfig... or at least would create two independent beans ("10" and "5") in case it sees AbstractConfig as an independant config.

While investigating this we also tried to register the method name on the MyConfig class:


public static class MyConfig extends AbstractConfig {

    @Bean(name = ["anotherName", "myBean"])
    public AtomicInteger myBean() {
    ...

and this time we got only one bean: anotherName : 5 (2109798150)

.. what was even more surprising for us.

Does anybody know if this is really the correct behaviour or are we only using it wrong? Should we raise a ticket in spring's jira? Thanks in advance!

What is your use case to make a spring java configuration abstract? — Daniel Hiller
We're using spring-data-mongodb and we're connecting to two different databases in our application. So we're overriding AbstractMongoConfiguration twice but have to rename some of the beans so we can find them in other places. But now we've seen that they're three times in our appCtx... — tvvk
Is this perhaps related to component scan path issues? Maybe you can avoid scanning the mongodb packages? Or is that required for spring data to work with mongodb? — Daniel Hiller
No it's not part of our classpath scanning. Only the two deriving classes are scanned automatically. — tvvk

Daniel Hiller Daniel Hiller · Accepted Answer · 2016-09-19T12:54:43

I'm not a Spring pro, but I'd say that behaviour is by design. To achieve what you want (I hope I guessed right) "inject this bean instead of the other" you would use @Primary on a bean, to selectively enable a configuration depending on circumstances you would use a @Conditional i.e. @Profile.

Spring java config extending an abstract configuration

2 Answers