Spring JAVA config tutorial

The classic way of configuring beans in Spring is using XML. But many programmers find switching between XML and java code annoying. Having to go into XML to debug dependencies and track down implementation classes has turned many programmers away from Spring. Since version 3.0, Spring has supported the ability to do configuration using classes and annotations without the need to use XML. In XML , to define a bean, you added to the application.xml
<bean id="Hello" class="com.mj.Hello"/>
To use the bean you wrote code like

ApplicationContext ac = new ClassPathXmlApplicationContext("application.xml") ; 
BeanFactory bf = (BeanFactory) ac ; 
Hello h = bf.getBean("Hello")
h.someMethod() ;

Let us write a new spring application using no XML.

Step1: Define the bean interface and implementation

public interface Greeting {
    public String getMessage() ;
}

public class NewYearGreeting implements Greeting {
    public String getMessage() {
        return "Happy New Year" ;
    }
}
public class BirthDayGreeting  implements Greeting {
    public String getMessage() {
        return "Happy Birthday" ;
    }
}

Step 2: Define the bean configuration in JAVA
The bean definitions are created by writing a class and annotating it with @Configuration. The individual beans are defined by annotating the method that creates the bean with @Bean.

@Configuration
public class GreetingSpringConfig {
    @Bean(name="newyear")
    public Greeting newyearGreeting() {
        return new NewYearGreeting() ;
    }
    @Bean(name="birthday")
    public Greeting birthdayGreeting() {
        return new BirthDayGreeting() ;
    }
 } 

Step 3: Use the beans from a client

 public class GreetingSample {
    public static void main(String args[]) {
        ApplicationContext ac = new    
        AnnotationConfigApplicationContext(GreetingSpringConfig.class) ;
        Greeting g = (Greeting) ac.getBean("newyear") ;
        System.out.println(g.getMessage()) ; 
        g = (Greeting) ac.getBean("birthday") ;
        System.out.println(g.getMessage()) ; 
} 

Note that instead of using ClassPathXmlApplicationContext ,we used AnnotationConfigApplicationContext. AnnotionConfigApplicationContext can process not just @Configuration annotated classes, but also JSR 330 annotated classes. If you don'nt like switching between JAVA & XML , then Java config is simple way of wiring your spring beans.