It is a combination of three annotations @ComponentScan, @EnableAutoConfiguration, and @Configuration.
@Required
It applies to the bean setter method.
It indicates that the beans with annotation must populate at configuration time with the required property, else it throws an exception BeanInitilizationException.
@Configuration
It is a class-level annotation.
It generates bean definitions and service requests.
@EnableAutoConfiguration
It auto-configures the bean that is present in the classpath and configures it to run the methods.
@Component
It is a class-level annotation.
It marks Java class as a bean.
A Java class with @Component annotation is looked for in the classpath.
If a class is found, the Spring Framework will configure it in the application context as a Spring Bean.
@ComponentScan
It scans a package for beans.
One can use this annotation along with the @Configuration annotation.
@Autowired
It auto wires spring bean on setter methods, instance variable, and constructor.
In other words, it allows automatic dependency injection. The spring container injects the dependent beans by matching data-type.
@Controller
The @Controller is a class-level annotation.
It marks the Java class as a web request handler.
By default, it returns a string that tells the route to redirect.
Some other annotations
@Bean
The @Bean is a method-level annotation.
It act as an alternative of XML <bean> tag.
This annotation tells the method to produce a bean that a Spring Container can manage.
@Service
It is a class-level annotation.
It tells the Spring that class contains business logic.
@Repository
It is a class-level annotation.
The repository is a DAO(Data Access Object) that access the database directly and perform all the operations related to the database.
@RequestMapping
It helps to map the web requests.
It consists of optional elements. For Instance consumes, header, method, name, params, path, produce, and value.
@GetMapping
It maps the HTTP GET requests on the specific handler method.
@PostMapping
It maps the HTTP POSTrequests on the specific handler method.
@PutMapping
It maps the HTTP PUT requests on the specific handler method.
@DeleteMapping
It maps the HTTP DELETE requests on the specific handler method.
@PatchMapping
It maps the HTTP PATCH requests on the specific handler method.
@RequestBody
It binds HTTP request with an object in a method parameter.
@ResponseBody
It binds the method return value to the response body.
@PathVariable
It extracts the values from the URI.
@RequestParam
It extracts the query parameters from the URL.
@RequestHeader
It helps us get the details about the HTTP request headers.
@RestController
It is a combination of @Controller and @ResponseBody annotations.Â
How does it work ?
@EnableAutoConfiguration annotation allows Spring Boot to automatically configure your application based on the dependencies you have added to the project.
The class that contains @SpringBootApplication annotation is the entry point of the spring boot application.
To run the Spring Boot application, this class should have the main method.
@SpringBootApplication annotation includes Auto- Configuration, Component Scan, and Spring Boot Configuration.
SpringApplication.run() inside the main method will bootstrap String application as a stand-alone application.
It creates an instance of ApplicationContext and loads all the beans.
