``++@ComponentScan++`` is used to find which Spring ``++@Component++`` beans (``++@Service++`` or ``++@Repository++`` or ``++Controller++``) are available in the classpath so they can be used in the application context. This is a convenient feature especially when you begin a new project but it comes with the drawback of slowing down the application start-up time especially when the application becomes bigger (ie: it references a large JAR file, or it references a significant number of JAR files, or the base-package refers to a large amount of .class files).


``++@ComponentScan++`` should be replaced by an explicit list of Spring beans loaded by ``++@Import++``.


The interface ``++@SpringBootApplication++`` is also considered by this rule because it is annotated with ``++@ComponentScan++``.


== Noncompliant Code Example

----
@ComponentScan
public class MyApplication {
...
}

@SpringBootApplication
public class MyApplication {
...
}
----


== Compliant Solution

----
@Configuration
@Import({
        DispatcherServletAutoConfiguration.class,
        ErrorMvcAutoConfiguration.class,
        HttpEncodingAutoConfiguration.class,
        HttpMessageConvertersAutoConfiguration.class,
        MultipartAutoConfiguration.class,
        ServerPropertiesAutoConfiguration.class,
        PropertyPlaceholderAutoConfiguration.class,
        WebMvcAutoConfiguration.class
})
public class MyApplication {
...
}
----


== See

* https://sites.google.com/site/appsdevelopersindia/google-blog/optimizingspringframeworkforappengineapplications[Optimizing Spring Framework for App Engine Applications]


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