[Spring]: Java Configuration

Methods to create a spring container

1. Full XML Config
2. Java Annotation
3. Java Configuration Class (No XML needed)

Java Configuration (No XML)

• Instead of configuring Spring contaner using XML, we can configure the Spring container only with Java code

Below two steps are the same as Java Annotation (2nd method)

@Configuration

Create a Java class and annotate as @Configuration

@Configuration
public class PlayerConfig {

}

@ComponentScan(optional)

• Add component scanning support

@Configuration
@ComponentScan("com.ellismin") // package to scan
public class PlayerConfig {

}

Read Spfing Java config class (new!) in main method

AnnotationConfigApplicationContext context = new AnnotationConfigApplicationContext(PlayerConfig.class);

• Different from ClassPathXmlApplicationContext since we don't use xml file anymore

Retrieve bean from spring contaner (same as previous)

Player player = context.getBean("swimPlayer", Player.class);

Define bean in Java config class (@Bean)

Defining bean is possible in the Java configuration class. These beans can be used without @ComponentScan

@Configuration
public class PlayerConfig {
    // Create instance of SunnyWeather and return it
    @Bean
    public Weather sunnyWeather() {
        return new sunnyWeather();
    }
    // Define bean for swim player AND inject dependency
    @Bean
    public Player swimPlayer() {
        SwimPlayer mySwimPlayer = new SwimPlayer();
        return mySwimPlayer;
    }
}

• sunnyWeather and swimPlayer will be the "bean id". This will be used when retriving the bean (in previous step)
• @Scope("ScopeName") can be added under @Bean for particular scoped beans

Reading values from properties file (@PropertySource)

• In xml configuration or Java annotation, it needed a piece of code
• With Java config, it can be achieved with @PropertySource in Java config class

@Configuration
@PropertySource("emailList.properties")
public class PlayerConfig {
    ...
}

• To obtain the value, it will be done in the same way as Java Annotations with @Value

public class BasketballPlayer implements Player {
    @Value("${john.email}")
    private String email;
    ...
}