The Java Programming language provided support for Annotations from Java 5.0.
Prior to annotations, the behaviour of the Spring Framework was largely controlled through XML
configuration. Today, the use of annotations provide us tremendous capabilities in how we configure the behaviours of the Spring Framework.
In this post, we’ll take a look at the annotations available in the Spring Framework.
@Required
This annotation is applied on bean setter methods. Consider a scenario where you need to enforce a required property. The @Required annotation indicates that the affected bean must be populated at configuration time with the required property. Otherwise an exception of type BeanInitializationException is thrown.
@Autowired
This annotation is applied on fields, setter methods, and constructors. The @Autowired annotation injects object dependency implicitly.
When you use @Autowired on fields and pass the values for the fields using the property name, Spring will automatically assign the fields with the passed values.
You can even use @Autowired on private properties also.
When you use @Autowired on setter methods, Spring tries to perform the by Type autowiring on the method. You are instructing Spring that it should initiate this property using setter method where you can add your custom code, like initializing any other property with this property.
When you use @Autowired on a constructor, constructor injection happens at the time of object creation. It indicates the constructor to autowire when used as a bean. One thing to note here is that only one constructor of any bean class can carry the @Autowired annotation.
@Qualifier
This annotation is used along with @Autowired annotation. When you need more control of the dependency injection process, @Qualifier can be used. @Qualifier can be specified on individual constructor arguments or method parameters. This annotation is used to avoid confusion which occurs when you create more than one bean of the same type and want to wire only one of them with a property.
@Value
This annotation is used at the field, constructor parameter, and method parameter level. The @Value annotation indicates a default value expression for the field or parameter to initialize the property with. As the @Autowired annotation tells Spring to inject object into another when it loads your application context, you can also use @Value annotation to inject values from a property file into a bean’s attribute. It supports both #{...} and ${...} placeholders.
@Bean
This annotation is used at the method level. @Bean annotation works with @Configuration to create Spring beans. As mentioned earlier, @Configuration will have methods to instantiate and configure dependencies. Such methods will be annotated with @Bean. The method annotated with this annotation works as bean ID and it creates and returns the actual bean.
Prior to annotations, the behaviour of the Spring Framework was largely controlled through XML
configuration. Today, the use of annotations provide us tremendous capabilities in how we configure the behaviours of the Spring Framework.
In this post, we’ll take a look at the annotations available in the Spring Framework.
@Required
This annotation is applied on bean setter methods. Consider a scenario where you need to enforce a required property. The @Required annotation indicates that the affected bean must be populated at configuration time with the required property. Otherwise an exception of type BeanInitializationException is thrown.
@Autowired
This annotation is applied on fields, setter methods, and constructors. The @Autowired annotation injects object dependency implicitly.
When you use @Autowired on fields and pass the values for the fields using the property name, Spring will automatically assign the fields with the passed values.
You can even use @Autowired on private properties also.
When you use @Autowired on setter methods, Spring tries to perform the by Type autowiring on the method. You are instructing Spring that it should initiate this property using setter method where you can add your custom code, like initializing any other property with this property.
When you use @Autowired on a constructor, constructor injection happens at the time of object creation. It indicates the constructor to autowire when used as a bean. One thing to note here is that only one constructor of any bean class can carry the @Autowired annotation.
@Qualifier
This annotation is used along with @Autowired annotation. When you need more control of the dependency injection process, @Qualifier can be used. @Qualifier can be specified on individual constructor arguments or method parameters. This annotation is used to avoid confusion which occurs when you create more than one bean of the same type and want to wire only one of them with a property.
@Value
This annotation is used at the field, constructor parameter, and method parameter level. The @Value annotation indicates a default value expression for the field or parameter to initialize the property with. As the @Autowired annotation tells Spring to inject object into another when it loads your application context, you can also use @Value annotation to inject values from a property file into a bean’s attribute. It supports both #{...} and ${...} placeholders.
@Bean
This annotation is used at the method level. @Bean annotation works with @Configuration to create Spring beans. As mentioned earlier, @Configuration will have methods to instantiate and configure dependencies. Such methods will be annotated with @Bean. The method annotated with this annotation works as bean ID and it creates and returns the actual bean.
That's it for today,
Hope to see you with another blog post,
Till then,
Good bye
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