Annotation in Spring Boot

To achieve dependency injection and different design goals we use annotations.

Following is the list of most commonly used annotations in Spring

👉1. @Component

use to make dependent class belong to Spring container. By default, it will create the object of the class in the Spring container using a singleton design pattern (only one object will be created).

Ex.

@Component

class Alpha extends Alien{......}

👉2. @Autowire

use to link objects available in Spring Container.

Ex.

@Autowire

Alien jaadoo;

👉3.  @Scope(value="prototype")

When we don't want to use the default singleton design pattern and want to create multiple objects when we ask for it only then.

Ex.

@Component

@Scope(value="prototype")

class Alpha extends Alien{......}

👉4. @Qualifier("name")

Use to give a specific name to the object in the spring container instead of the default name.

Ex.

@Component("jadoo")

class Alpha extends Alien{......}

class T{

@Autowire

@Qualifier("jadoo")

Alien jaadoo;

}

In the above example, the default name is alpha but we changed it to jadoo by using annotation.

👉5. @ConditionalOnProperty( propertyName = "do something")

Use to set(enable/disable) some conditions based on property.

For example, we want to enable the scheduling of some tasks based on the time we can use this annotation.

@ConditionalOnProperty(name = ""spring.enable.scheduling" )

👉6. @Scheduled(cron = "${schedularName}")

Use to schedule tasks based on time and time will be defined in the application.properties based on schedularName.

👉7. @Entity("EntityName")

By default entity name is class name Entity represents POJO which is persistence to the database. One entity iteration is equal to 1 row in the table. 

👉8. @Table(name = "TABLE_NAME")

Represents table name in database.

👉9. @Id

Represents the primary key of the database.

👉10.@Column

Represent column Name in Table.

👉11.@Repository

It represents the class is a repository we extend Repo also to use default methods like save, saveAll etc.