Overview of SpringBoot, JPA, Global Exception Handling, and Spring Cloud Annotations

1. SpringBoot / Spring Annotations

@SpringBootApplication combines @Configuration, @EnableAutoConfiguration, and @ComponentScan and is typically placed on the main class.

@Repository marks a DAO component; @Service marks a business‑logic component; @RestController combines @Controller and @ResponseBody for REST endpoints; @Controller is used for MVC controllers that return views; @Component is a generic stereotype for beans that do not fit other categories.

@ResponseBody forces the method return value to be written directly to the HTTP response body, useful for asynchronous JSON responses.

@RequestBody binds the request body (usually JSON) to a method parameter, indicating the parameter is required.

@ComponentScan scans for classes annotated with @Component, @Controller, @Service, etc., and registers them as beans.

@Configuration designates a class as a source of bean definitions, similar to an XML configuration file.

@Bean declares a method that produces a bean to be managed by the Spring container.

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

@Autowired performs by‑type injection; adding required=false makes the injection optional.

@Qualifier specifies which bean to inject when multiple candidates of the same type exist.

@Resource(name="name", type="type") performs injection by name (default) and can also specify a type.

@RequestMapping maps HTTP requests to handler methods and can be applied at class or method level. Its six attributes include params, headers, value, method, consumes, and produces.

@GetMapping, @PostMapping, etc., are shortcut annotations for specific HTTP methods.

@RequestParam binds a request parameter to a method argument; @PathVariable binds a URI template variable.

public String getByMacAddress(@PathVariable("macAddress") String macAddress) {
    // do something;
}

2. JPA Annotations

@Entity marks a class as a JPA entity; @Table(name="...") specifies the table name (optional if it matches the entity name).

@MappedSuperclass designates a superclass whose mapping information is inherited by subclasses.

@NoRepositoryBean prevents Spring Data from instantiating a repository interface.

@Column maps a field to a column; it can be omitted when names match.

@Id denotes the primary key; @GeneratedValue(strategy=GenerationType.SEQUENCE, generator="repair_seq") defines a sequence‑based key generation strategy.

@SequenceGenerator configures the sequence name and allocation size.

@Transient tells the ORM to ignore a field.

@Basic(fetch=FetchType.LAZY) controls lazy loading of a field.

@JsonIgnore excludes a property from JSON serialization/deserialization.

@JoinColumn(name="loginId") defines a foreign‑key column for one‑to‑one or one‑to‑many relationships.

@OneToOne, @OneToMany, @ManyToOne describe entity relationships.

3. Global Exception Handling

@ControllerAdvice (which includes @Component) enables centralized exception handling across all controllers.

@ExceptionHandler(Exception.class) marks a method to handle a specific exception type.

4. Spring Cloud Annotations

@EnableEurekaServer turns a Spring Boot application into a Eureka service registry.

@EnableDiscoveryClient makes a service discoverable by the registry.

@LoadBalanced enables client‑side load balancing for RestTemplate.

@EnableCircuitBreaker activates circuit‑breaker functionality.

@HystrixCommand(fallbackMethod="backMethod") defines a fallback method for a protected call.

@EnableConfigServer creates a configuration server.

@EnableZuulProxy enables Zuul routing.

@SpringCloudApplication aggregates @SpringBootApplication, @EnableDiscoveryClient, and @EnableCircuitBreaker for convenience.