Spring @Bean autowire() - fails the second (?) time

Question

Ok, so, I have a config class that creates two beans. They are defined as the following:

public class FileUploadConfiguration {

    public static final String UPLOAD_PREFIX = "file.upload";

    @Bean(name = "fileService", autowire = Autowire.BY_TYPE)
    @DependsOn("fileUploadPaths")
    @Autowired
    public CRUDFileService fileService(@Qualifier("fileUploadPaths") PrefixedPropertyFactoryBean fileUploadPaths) throws Exception {
        Map<String, String> paths = Maps.fromProperties(fileUploadPaths.getObject());
        return new CRUDFileService(File.class.getName(), paths);
    }

    @Bean(name = "fileUploadPaths")
    public PrefixedPropertyFactoryBean fileUploadPaths(Environment environment) {
        PrefixedPropertyFactoryBean fileUploadPaths = new PrefixedPropertyFactoryBean();
        fileUploadPaths.setPrefix(UPLOAD_PREFIX);
        fileUploadPaths.setLocations(ResourceUtils.getActiveResources(environment));
        return fileUploadPaths;
    }
}

If I put breakpoints in both instantiations, the flow is the following:

1) fileUploadPaths is instantiated, and it looks correct to me.

2) fileService gets instantiated, but through the postProcessPropertyValues of FileUploadConfiguration bean creation.. this seems weird to me.

3) After that, I get an exception, because it seems Spring tries to create fileService again, but now through the createBean, and for some reason the @Qualifier on the parameter definition seems to be ignored.

Exception in thread "main" org.springframework.beans.factory.UnsatisfiedDependencyException: Error creating bean with name 'fileService' defined in class x.y.z.FileUploadConfiguration: Unsatisfied dependency expressed through constructor argument with index 0 of type [a.b.c.PrefixedPropertyFactoryBean]: Ambiguous factory method argument types - did you specify the correct bean references as factory method arguments? at org.springframework.beans.factory.support.ConstructorResolver.createArgumentArray(ConstructorResolver.java:735) at org.springframework.beans.factory.support.ConstructorResolver.instantiateUsingFactoryMethod(ConstructorResolver.java:464) at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.instantiateUsingFactoryMethod(AbstractAutowireCapableBeanFactory.java:1119) at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.createBeanInstance(AbstractAutowireCapableBeanFactory.java:1014) at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.doCreateBean(AbstractAutowireCapableBeanFactory.java:504) at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.createBean(AbstractAutowireCapableBeanFactory.java:476) at org.springframework.beans.factory.support.AbstractBeanFactory$1.getObject(AbstractBeanFactory.java:303) at org.springframework.beans.factory.support.DefaultSingletonBeanRegistry.getSingleton(DefaultSingletonBeanRegistry.java:230) at org.springframework.beans.factory.support.AbstractBeanFactory.doGetBean(AbstractBeanFactory.java:299) at org.springframework.beans.factory.support.AbstractBeanFactory.getBean(AbstractBeanFactory.java:194) at org.springframework.beans.factory.support.DefaultListableBeanFactory.preInstantiateSingletons(DefaultListableBeanFactory.java:755) at org.springframework.context.support.AbstractApplicationContext.finishBeanFactoryInitialization(AbstractApplicationContext.java:757) at org.springframework.context.support.AbstractApplicationContext.refresh(AbstractApplicationContext.java:480) at org.springframework.boot.context.embedded.EmbeddedWebApplicationContext.refresh(EmbeddedWebApplicationContext.java:118)

NOTE: This is fixed if I change fileService definition to the following:

@Bean(name = "fileService")
@DependsOn("fileUploadPaths")
@Autowired
public CRUDFileService fileService(@Qualifier("fileUploadPaths") PrefixedPropertyFactoryBean fileUploadPaths, AutowireCapableBeanFactory factory) throws Exception {
    Map<String, String> paths = Maps.fromProperties(fileUploadPaths.getObject());
    CRUDFileService crudFileService = new CRUDFileService(File.class.getName(), paths);
    factory.autowireBean(crudFileService);
    return crudFileService;
}

So, instead of letting Spring autowire my bean through @Bean(autowire = Autowire.BY_TYPE), I simply autowire the AutowireCapableBeanFactory and autowire the CRUDFileService bean myself.

My question is: Why does such behavior happen? Am I using @Bean(autowire = Autowire.BY_TYPE) correctly? I've used it before like that and it worked like a charm, except I didn't autowire the bean method parameters like I did with this one.

Answer 1

The issue that I see is that you are trying to inject a Spring FactoryBean as a dependency into another bean. FactoryBean is special though, it is a factory for a bean and the resulting bean is what you should inject into other objects.

So assuming that your dependency in CRUDFileService is a Properties class instead of the FactoryBean, if you are to try this, it should work cleanly:

public class FileUploadConfiguration {

    public static final String UPLOAD_PREFIX = "file.upload";

    @Bean(name = "fileService", autowire = Autowire.BY_TYPE)
    @Autowired
    public CRUDFileService fileService(@Qualifier("fileUploadPaths") Properties fileUploadPaths) throws Exception {
        Map<String, String> paths = Maps.fromProperties(fileUploadPaths);
        return new CRUDFileService(File.class.getName(), paths);
    }

    @Bean(name = "fileUploadPaths")
    public PrefixedPropertyFactoryBean fileUploadPaths(Environment environment) {
        PrefixedPropertyFactoryBean fileUploadPaths = new PrefixedPropertyFactoryBean();
        fileUploadPaths.setPrefix(UPLOAD_PREFIX);
        fileUploadPaths.setLocations(ResourceUtils.getActiveResources(environment));
        return fileUploadPaths;
    }
}