About Spring Annotations

@Entity

• Annotates class signature
• Description:
  • Allows the persistence provider to recognize it as a persistence class.
  • An object representative of a snap shot of data from a database.
  • By default, maps this entity to a table whose name is the name of the annotated class. Can be rerouted via the @Table annotation
  • Entities are said to be fungible, or mutually interchangeable.
• Pre-requesites for use:
  • An interface cannot be an entity.
  • An enum cannot be an entity.
  • The class can be abstract or concrete.
  • The class must define a no-arg constructor.
  • Each Entity must be annotated with a respective ID.

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@Id

• Annotates field declarations
• Description:
  • Denotes the primary key for this Entity.
  • Can be generated manually by application or by automatically by the persistence provider.
• Pre-requisites for use:
  • Class must be annotated with @Entity

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@GeneratedValue(strategy = GenerationType.ENUM_VALUE)

• Annotates Id fields.
• Description:
  • Specifies how the persistence provider will generate this value.
  • GenerationType.SEQUENCE - specifies the use of database SQL sequence
  • GenerationType.IDENTITY - uses a database identity column
  • GenerationType.TABLE - instructs provider to store the sequence name and its current value in a table, increasing the value of each time a new instance of the entity is persisted.
  • GenerationType.AUTO - default when nothing specified. Provider does generation of a key automatically. It will select an appropriate strategy for a particular database.
• Pre-requesites for use:
  • Field must be annotated with @Id.

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@Autowired

• Annotates field declaration or method-parameters
• Description
  • injects bean by type
  • can be used alone.
  • If is used alone, it will be wired by type
  • If more than one bean of same type are declared in the container @Autowired does not know which beans to use for injection.
• Pre-requesites for use:
  • Field-type must be annotated with some form of @Component.

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@Component

• Annotates class signature
• Description
  • denotes that Spring framework will autodetect these classes for dependency injection when annotation-based configuration and classpath scanning is used.
• Prerequisites for use:
  • none

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@Service

• Annotates class signature
• Description
  • specialized form of @Component
  • responsible for performing service tasks
  • in many case you use this annotation for best practice, but isn’t always necessary.
• Prerequisites for use:
  • none

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@Controller

• Annotates class signature
• Description
  • specialized form of @Component
  • indicates that a particular class serves the role of a controller
  • acts as a stereotype for the annotated class, indicating its role
  • dispatcher scans such annotated classes for mapped methods and detects @RequestMapping annotations
• Pre-requesites for use:
  • none

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@RequestMapping

• Annotates a method signature
• Description
  • annotation maps HTTP requests to handler methods of MVC and REST controllers.
• Pre-requesites for use
  • class must be a annotated with @Controller

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@PathVariable

• Annotates a method parameter
• Description
  • indicates that a method parameter should be bound to a URI template variable
• Pre-requesites for use
  • class must be a annotated with @Controller

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@RequestParam

• Annotates a method parameter
• Description
  • indicates that a method parameter should be bound to a web request parameter
  • used to extract query parameters, form parameters
• Pre-requesites for use
  • class must be a annotated with @Controller