Combining Annotation and XML Configurations in your Spring 3 Applications

Spring 3 provides the ability to use a Java based configuration file, as opposed to using those monolithic XML configuration files that everyone hates. However, it doesn't have to be a complete "annotations vs. xml" debate, as you can easily combine both approaches.

If you are using a Java @Configuration file, you can simultaneously load in an XML configuration file simply by adding an @ImportResource annotation. The following annotation loads in a Spring XML configuration file named meanbeans.xml into the annotation based Spring ApplicationContext object:

@Configuration
@ImportResource("classpath:meanbeans.xml")
class JConfig { }

So, if you've got a class named FooBean and a class named BarBean, and you have one bean configured in the XML file, and the other configured in the Java @Configuration file, you can pull them both into your application from a single beanFactory.

class FooBean { }
class BarBean { }

So, this would be the goal:

public class XmlAndAnnotations {

  public static void main(String args[]) {
    AnnotationConfigApplicationContext beanFactory =
    new AnnotationConfigApplicationContext(JConfig.class);
      //new ClassPathXmlApplicationContext("meanbeans.xml");

    System.out.println(beanFactory.getBean("fooBean"));
    System.out.println(beanFactory.getBean("barBean"));
  }
}

Notice how both the fooBean and barBean are pulled from a common beanFactory, despite the two beans being configured in different configuration resources? Here's the full Java based configuration file, which only specifically describes the creation of the fooBean:

@Configuration
@ImportResource("classpath:meanbeans.xml")
class JConfig {
  @Bean()
  public FooBean fooBean() {return new FooBean();}
}

And here's the meanbeans.xml file, which describes the barBean:

And that's it! When the main method of the XmlAndAnnotations class runs, both the fooBean and barBean will be loaded from two separate Spring configuration resources!

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Recommended Books for Learning Spring

Spring in Action  ~ Craig Walls
Spring Recipes: A Problem-Solution Approach  ~ Gary Mak
Professional Java Development with the Spring Framework ~ Rod Johnson PhD
Pro Java EE Spring Patterns: Best Practices and Design Strategies ~ Dhrubojyoti Kayal