[java] How to scan multiple paths using the @ComponentScan annotation?

I'm using Spring 3.1 and bootstrapping an application using the @Configuration and @ComponentScan attributes.

The actual start is done with

new AnnotationConfigApplicationContext(MyRootConfigurationClass.class);

This Configuration class is annotated with

@Configuration
@ComponentScan("com.my.package")
public class MyRootConfigurationClass

and this works fine. However I'd like to be more specific about the packages I scan so I tried.

@Configuration
@ComponentScan("com.my.package.first,com.my.package.second")
public class MyRootConfigurationClass

However this fails with errors telling me it can't find components specified using the @Component annotation.

What is the correct way to do what I'm after?

Thanks

Another way of doing this is using the basePackages field; which is a field inside ComponentScan annotation.

@ComponentScan(basePackages={"com.firstpackage","com.secondpackage"})

If you look into the ComponentScan annotation .class from the jar file you will see a basePackages field that takes in an array of Strings

public @interface ComponentScan {
String[] basePackages() default {};
}

Or you can mention the classes explicitly. Which takes in array of classes

Class<?>[]  basePackageClasses

You use ComponentScan to scan multiple packages using

@ComponentScan({"com.my.package.first","com.my.package.second"})

There is another type-safe alternative to specifying a base-package location as a String. See the API here, but I've also illustrated below:

@ComponentScan(basePackageClasses = {ExampleController.class, ExampleModel.class, ExmapleView.class})

Using the basePackageClasses specifier with your class references will tell Spring to scan those packages (just like the mentioned alternatives), but this method is both type-safe and adds IDE support for future refactoring -- a huge plus in my book.

Reading from the API, Spring suggests creating a no-op marker class or interface in each package you wish to scan that serves no other purpose than to be used as a reference for/by this attribute.

IMO, I don't like the marker-classes (but then again, they are pretty much just like the package-info classes) but the type safety, IDE support, and drastically reducing the number of base packages needed to include for this scan is, with out a doubt, a far better option.

Provide your package name separately, it requires a String[] for package names.

Instead of this:

@ComponentScan("com.my.package.first,com.my.package.second")

Use this:

@ComponentScan({"com.my.package.first","com.my.package.second"})

I use:

@ComponentScan(basePackages = {"com.package1","com.package2","com.package3", "com.packagen"})

You can also use @ComponentScans annotation:

@ComponentScans(value = { @ComponentScan("com.my.package.first"),
                          @ComponentScan("com.my.package.second") })

make sure you have added this dependency in your pom.xml

<dependency>
    <groupId>org.springframework.boot</groupId>
    <artifactId>spring-boot-starter-web</artifactId>
</dependency>