When working with the Spring Boot framework, annotations play a crucial role in providing metadata and configuration information for your applications. In this blog, we'll dive into some of the most important Spring Boot annotations and their applications. ๐
Core Spring Framework Annotations
Required ๐ ๏ธ
The @Required
annotation is applied to bean setter methods. It indicates that the annotated bean must be populated with the required property at configuration time. If not, it throws an exception (BeanInitializationException
). For example:
public class Machine {
private Integer cost;
@Required
public void setCost(Integer cost) {
this cost = cost;
}
}
Autowired ๐ค
Spring provides annotation-based auto-wiring with @Autowired
. It's used to autowire Spring beans on setter methods, instance variables, and constructors. When you use @Autowired
, the Spring container auto-wires the bean by matching data types. For example:
@Component
public class Customer {
private Person person;
@Autowired
public Customer(Person person) {
this person = person;
}
}
Configuration โ๏ธ
The @Configuration
annotation is used at the class level. Classes annotated with @Configuration
are used by Spring Containers as a source of bean definitions. For example:
@Configuration
public class Vehicle {
@Bean
public Vehicle engine() {
return new Vehicle();
}
}
ComponentScan ๐ก
@ComponentScan
is used when you want to scan a package for beans. It is often used in conjunction with the @Configuration
annotation and you can specify base packages to scan for Spring components. For example:
@ComponentScan(basePackages = "com.javatpoint")
@Configuration
public class ScanComponent {
// ...
}
Bean โ
The @Bean
annotation is used at the method level. It is an alternative to the XML <bean>
tag and tells the method to produce a bean managed by the Spring Container. For example:
@Bean
public BeanExample beanExample() {
return new BeanExample();
}
Spring Framework Stereotype Annotations
Component ๐งฉ
@Component
is a class-level annotation used to mark a Java class as a bean. Classes annotated with @Component
are discovered during the classpath scanning and configured as Spring Beans. For example:
@Component
public class Student {
// ...
}
Controller ๐ฎ
@Controller
is a specialization of @Component
and is often used to serve web pages. It marks a class as a web request handler and is typically used with the @RequestMapping
annotation. For example:
@Controller
@RequestMapping("books")
public class BooksController {
// ...
}
Service ๐ ๏ธ
The @Service
annotation is used at the class level to indicate that the class contains business logic. For example:
@Service
public class TestService {
public void service1() {
// business code
}
}
Repository ๐๏ธ
@Repository
is a class-level annotation commonly used for Data Access Objects (DAOs) that access databases directly. For example:
@Repository
public class TestRepository {
public void delete() {
// persistence code
}
}
Spring Boot Annotations
EnableAutoConfiguration and SpringBootApplication๐
@EnableAutoConfiguration
auto-configures beans present in the classpath.@SpringBootApplication
combines@EnableAutoConfiguration
,@ComponentScan
, and@Configuration
.
Spring MVC and REST Annotations
RequestMapping ๐
@RequestMapping
is used to map web requests and has various optional elements like consumes
, header
, method
, name
, params
, path
, produces
, and value
. It can be used with both classes and methods.
HTTP Request Method Annotations ๐
@GetMapping
,@PostMapping
,@PutMapping
,@DeleteMapping
, and@PatchMapping
are used to map HTTP request methods to specific handler methods.
Request and Response Annotations ๐
@RequestBody
binds an HTTP request to a method parameter.@ResponseBody
binds the method return value to the response body.@PathVariable
extracts values from the URI.@RequestParam
extracts query parameters from the URL.@RequestHeader
gets details about HTTP request headers.
RestController ๐ฎ
@RestController
combines @Controller
and @ResponseBody
annotations, eliminating the need to annotate each method with @ResponseBody
.
RequestAttribute ๐ท๏ธ
@RequestAttribute
binds a method parameter to a request attribute.
With this guide, you have a solid understanding of key Spring Boot annotations and their applications. Annotations simplify the configuration and development of Spring Boot applications, making your journey into Spring Boot development smoother and more efficient. Happy coding! ๐