Spring Boot Annotations: @SpringBootApplication, @RestController & JPA Basics

1. Annotation List

@SpringBootApplication : combines @ComponentScan, @Configuration and @EnableAutoConfiguration.

@Configuration : equivalent to XML configuration, provides type‑safe Java config.

@EnableAutoConfiguration : enables Spring Boot’s auto‑configuration based on classpath.

@ComponentScan : scans for components such as @Component, @Service, @Repository.

@Component : generic stereotype for a Spring‑managed component.

@RestController : combination of @Controller and @ResponseBody for REST‑style controllers.

@Autowired : injects bean dependencies automatically.

@PathVariable : binds URI template variables to method parameters.

@JsonBackReference : solves circular reference problems during JSON serialization.

@RepositoryRestResource : works with spring‑boot‑starter‑data‑rest.

2. Detailed Annotation Usage

@SpringBootApplication : declares that Spring Boot should auto‑configure the application; equivalent to using @Configuration, @EnableAutoConfiguration and @ComponentScan together.

package com.example.myproject;
import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;

@SpringBootApplication // same as @Configuration @EnableAutoConfiguration @ComponentScan
public class Application {
    public static void main(String[] args) {
        SpringApplication.run(Application.class, args);
    }
}

@ResponseBody : writes the method return value directly to the HTTP response body, useful for returning JSON from asynchronous calls.

@RequestMapping("/test")
@ResponseBody
public String test() {
    return "ok";
}

@Controller and @RequestMapping : define a controller class and map URLs to handler methods.

@Controller
@RequestMapping("/demoInfo")
public class DemoController {
    @Autowired
    private DemoInfoService demoInfoService;

    @RequestMapping("/hello")
    public String hello(Map map) {
        System.out.println("DemoController.hello()");
        map.put("hello", "from TemplateController.helloHtml");
        return "/hello";
    }
}

@RestController and @RequestMapping example:

@RestController
@RequestMapping("/demoInfo2")
public class DemoController2 {
    @RequestMapping("/test")
    public String test() {
        return "ok";
    }
}

@EnableAutoConfiguration : attempts to configure the application automatically based on the jars present on the classpath (e.g., provides an in‑memory HSQLDB if no datasource is defined).

@ComponentScan : automatically discovers beans annotated with @Component, @Service, @Repository, etc., within the package of the annotated class and its sub‑packages.

@Configuration , @Import , @ImportResource : Java‑based configuration alternatives to XML.

@Bean : declares a bean produced by a method.

@Value : injects property values from application.properties.

@Inject : same as @Autowired without required attribute.

@Qualifier : disambiguates injection when multiple beans of the same type exist.

@Resource : similar to @Autowired, defaults to byName injection.

3. JPA Annotations

@Entity (often paired with @Table) marks a class as a JPA entity.

@MappedSuperclass : defines a base class whose properties are inherited by entity subclasses.

@NoRepositoryBean : indicates that a repository interface should not be instantiated.

@Column : maps a field to a database column; can be omitted if names match.

@Id and @GeneratedValue : designate the primary key and its generation strategy.

@SequenceGenerator : defines a database sequence for key generation.

@Transient : excludes a field from persistence.

@JsonIgnore : prevents a property from being serialized to JSON.

@JoinColumn , @OneToOne , @OneToMany , @ManyToOne : define relationships between entities.

4. Spring MVC Annotations

@RequestMapping : maps URLs to controller classes or methods; supports attributes such as params, headers, method, consumes, produces.

@RequestParam : binds request parameters to method arguments.

@PathVariable : binds URI template variables to method arguments.

5. Global Exception Handling

@ControllerAdvice : a component that applies to all controllers for cross‑cutting concerns like exception handling.

@ExceptionHandler : defines a method to handle specific exception types.