Spring Configuration annotation indicates that the class has @Bean definition methods.
Spring @Bean Annotation is applied on a method to specify that it returns a bean to be managed by the Spring context.
@Configuration
public class ApplicationConfig {
@Bean
public DataSource dataSource() {
return new DataSource();
}
}
Spring will create as many beans as we define in the @Configuration classes. @Configuration classes are beans too.
public class MySpringApp {
public static void main(String[] args) {
// Create the application from the configuration
ApplicationContext ctx = SpringApplication.run(ApplicationConfig.class);
// Look up the application service interface
// Way 1: Casting
DataSource ds1 = (DataSource) ctx.getBean("dataSource");
// Way 2: Use typed method
DataSource ds2 = ctx.getBean("dataSource", DataSource.class);
// Way 3: Without been id if type is unique
DataSource ds3 = ctx.getBean(DataSource.class);
// Use the application
ds1.close();
ds2.close();
ds3.close();
}
}
Creating an Application Context from Multiple Files
@Configuration
@Import({ApplicationConfig.class, WebConfig.class})
public class InfraetructureConfig {
@Bean
public DataSource dataSource() {
return new DataSource();
}
}
Beware of duplicate beans. In the previous code, if ApplicationConfig.class and WebConfig.class have the same bean id you get the bean from WebConfig because it is the last bean. To avoid that you can use the @Order annotation.
@Configuration
@Order(1)
public class ApplicationConfig {
@Bean
public String example(){
return new String("example");
}
}
Bean Scope
The default scope is singleton
DataSource ds1 = (DataSource) ctx.getBean("dataSource");
DataSource ds2 = (DataSource) ctx.getBean("dataSource");
assert ds1 == ds2; // True - Same object
Prototype Scope: a new instance is created every time the bean is referenced.
@Bean
@Scope("prototype")
public DataSource dataSource() {
return new DataSource();
}
DataSource ds1 = (DataSource) ctx.getBean("dataSource");
DataSource ds2 = (DataSource) ctx.getBean("dataSource");
assert ds1 != ds2; // True - Diferent objects
Other scopes:
- session
- request
- application
- global
- thread
- websocket
- refresh
- Custom scopes
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