Spring configuration class loading order with spring-boot @ConditionalOnMissingBean?

Question

I'd like to enable custom configuration and sensible defaults using @ConditionalOnMissingBean? I have a spring boot application:

@Configuration
@Import({CustomConfiguration.class, DefaultConfiguration.class})
@EnableAutoConfiguration(exclude={MetricFilterAutoConfiguration.class})
public class Application {

    @Autowired
    ErrorListener errorListener;
}

and a CustomConfiguration that allows for either Spring xml or component scanning:

@Configuration("customConfiguration")
@ImportResource("classpath:customContext.xml")
@ComponentScan({"org.custom.impl"})
public class CustomConfiguration

The DefaultConfiguration uses ConditionalOnMissingBean:

@Bean
@ConditionalOnMissingBean 
ErrorListener errorListener() {
     return new LoggingErrorListener();
}

What I'm trying to achieve is allow for a custom ErrorListener to be defined in the classpath, if not defined then use the default LoggingErrorListener (via the ConditionalOnMissingBean). I'm finding that the DefaultConfiguration is always being used before the CustomConfiguration.

I've been experimenting with @DependsOn and @Order but no joy.

Answer 1

I wouldn't use @ConditionalOnMissingBean outside of an auto-configuration class if I were you, unless you can control the order of import of @Configuration classes. Auto-configuration does it explicitly, but normal user config classes (especially if they are @ComponentSCanned) do not have a defined order.