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Spring Boot Cheat Sheet

Spring Boot 備忘單

註解

Annotation	Description	Example
@SpringBootApplication	Marks a class as a Spring Boot application. Enables auto-configuration and component scanning.	@SpringBootApplication
@RestController	Indicates that a class provides RESTful endpoints. It combines @Controller and @ResponseBody annotations.	@RestController
@RequestMapping	Maps HTTP requests to handler methods of RESTful controllers.	@RequestMapping("/api")
@Autowired	Injects dependencies into a Spring bean. It can be used for constructor, setter, or field injection.	@Autowired private MyService myService;
@Component	Indicates that a class is a Spring-managed component. It is automatically detected during component scanning.	@Component
@Repository	Marks a class as a Spring Data repository. It handles data access and persistence logic.	@Repository
@Service	Marks a class as a service component in the business layer. It is used to separate business logic from presentation logic.	@Service
@Configuration	Indicates that a class provides bean definitions. It is used along with @bean to define beans in Java-based configuration.	@Configuration
@Value	Injects values from properties files or environment variables into Spring beans.	@Value("${my.property}") private String property;

控制流程

初始化：Spring Boot 首先載入應用程式屬性和自動配置 bean。
元件掃描：Spring 掃描控制器、服務和儲存庫等元件。
Bean 建立：Spring 建立 Bean 並使用依賴注入解析依賴關係。
請求處理：傳入的 HTTP 請求根據請求對應對應到控制器方法。
執行：控制器方法處理請求、與服務互動並回傳回應。
回應渲染：Spring 將方法回傳值轉換為適當的 HTTP 回應（例如 JSON）。

Spring Boot 備忘單的錯誤處理

錯誤處理是建立健全應用程式的關鍵方面。 Spring Boot 提供了多種優雅處理錯誤和異常的機制，確保流暢的使用者體驗。

錯誤類型

客戶端錯誤：無效客戶端請求導致的錯誤，例如 400 Bad Request 或 404 Not Found。
伺服器錯誤：伺服器端發生的錯誤，例如500內部伺服器錯誤。
驗證錯誤：由於輸入無效或資料驗證失敗而導致的錯誤。

錯誤處理機制

1. 控制者建議

@ControllerAdvice：用於在 Spring MVC 中定義全域異常處理程序的註解。
@ExceptionHandler：用於處理控制器建議中的特定例外的註解。
範例：

@ControllerAdvice
public class GlobalExceptionHandler {

    @ExceptionHandler(MyException.class)
    public ResponseEntity<ErrorResponse> handleMyException(MyException ex) {
        ErrorResponse response = new ErrorResponse("My error message");
        return new ResponseEntity<>(response, HttpStatus.BAD_REQUEST);
    }

    @ExceptionHandler(Exception.class)
    public ResponseEntity<ErrorResponse> handleException(Exception ex) {
        ErrorResponse response = new ErrorResponse("Internal server error");
        return new ResponseEntity<>(response, HttpStatus.INTERNAL_SERVER_ERROR);
    }
}

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回應實體異常處理程序

ResponseEntityExceptionHandler：處理常見 Spring MVC 異常的基底類別。
重寫：重寫handleMethodArgumentNotValid、handleHttpMessageNotReadable等方法
範例：

@ControllerAdvice
public class CustomExceptionHandler extends ResponseEntityExceptionHandler {

@Override
protected ResponseEntity<Object> handleMethodArgumentNotValid(
        MethodArgumentNotValidException ex, HttpHeaders headers, HttpStatus status, WebRequest request) {
    ErrorResponse response = new ErrorResponse("Validation failed");
    return new ResponseEntity<>(response, HttpStatus.BAD_REQUEST);
}

// Other overrides for handling specific exceptions

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3. 錯誤屬性

ErrorAttributes：用於自訂錯誤回應內容和格式的介面。
DefaultErrorAttributes：Spring Boot 提供的預設實作。

@Component
public class CustomErrorAttributes extends DefaultErrorAttributes {
@Override
public Map<String, Object> getErrorAttributes(WebRequest webRequest, boolean includeStackTrace) {
    Map<String, Object> errorAttributes = super.getErrorAttributes(webRequest, includeStackTrace);
    errorAttributes.put("customAttribute", "Custom value");
    return errorAttributes;
}

}

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