JSR 303 Data Validation

Built-in Validation Annotations

Apply the @Valid annotation to controller methods requiring validation. Use annotations from javax.validation.constraints on fields in value objects to enforce constraints with custom messages.

Group-Based Validation

Group validation handles scenarios like ensuring an ID is null for creation but present for updates. Define group marker interfaces and use @Validated with the appropriate group class from org.springframework.validation.annotation.

Object Type Classifications

• PO (Persistent Object): Represents a database record, excluding any database operations.
• DO (Domain Object): A business entity abstracted from the real world.
• TO (Transfer Object): Facilitates data transfer between applications.
• DTO (Data Transfer Object): Transefrs data between service and presentation layers, optimizing distributed calls.
• VO (Value Object): Used for business layer data transfer, abstracted from business needs, created via new and garbage-collected. As a view object, it encapsulates data for page rendering or input.
• BO (Business Object): Encapsulates business logic, often combining multiple POs or VOs.
• POJO (Plain Ordinary Java Object): A simple Java object with properties and accessors, encompassing DO, DTO, BO, and VO.
• DAO (Data Access Object): Provides database CRUD operations, acting as an interface between business logic and data resources.

Layered Naming Conventions

Domain Model Specifications

• DO (Data Object): Maps directly to database tables, transmitted via DAO layer.
• DTO (Data Transfer Object): Output from Service or Manager layers.
• BO (Business Object): Business logic encapsulation from Service layer.
• AO (Application Object): Reusable model between Web and Service layers, close to presentation.
• VO (View Object): Transfers data to template rendering engines.
• Query: Encapsulates search requests; avoid using Map for parameters exceeding two.

Naming Rules

• Data objects: xxxDO, where xxx is the table name.
• Data transfer objects: xxxDTO, with xxx as business domain name.
• View objects: xxxVO, typically matching page names.
• POJO is a collecitve term; avoid naming as xxxPOJO.

Service/DAO Method Naming

• Retrieve single: prefix get.
• Retrieve multiple: prefix list with plural suffix (e.g., listItems).
• Count: prefix count.
• Insert: prefix save or insert.
• Delete: prefix remove or delete.
• Update: prefix update.

Global Code Handling

Cross-Origin Configuration

@Configuration
public class CorsConfig {
    @Bean
    public CorsWebFilter corsFilter() {
        UrlBasedCorsConfigurationSource configSource = new UrlBasedCorsConfigurationSource();
        CorsConfiguration config = new CorsConfiguration();
        config.setAllowedHeaders(Arrays.asList("*"));
        config.setAllowedMethods(Arrays.asList("*"));
        config.setAllowedOrigins(Arrays.asList("*"));
        config.setAllowCredentials(true);
        configSource.registerCorsConfiguration("/**", config);
        return new CorsWebFilter(configSource);
    }
}

Exception Handling

@RestControllerAdvice(basePackages = "com.example.product.web")
public class GlobalExceptionHandler {
    @ExceptionHandler(MethodArgumentNotValidException.class)
    public Response handleValidationError(MethodArgumentNotValidException ex) {
        BindingResult result = ex.getBindingResult();
        Map<String, String> errors = new HashMap<>();
        result.getFieldErrors().forEach(error -> 
            errors.put(error.getField(), error.getDefaultMessage()));
        return Response.fail(ErrorCode.VALIDATION_FAILED, errors);
    }

    @ExceptionHandler(Exception.class)
    public Response handleGenericError(Exception e) {
        return Response.fail(ErrorCode.SYSTEM_ERROR);
    }
}

Business Status Codes

public enum ErrorCode {
    SYSTEM_ERROR(10000, "System error occurred"),
    VALIDATION_FAILED(10001, "Input validation failed");

    private final int code;
    private final String message;

    ErrorCode(int code, String message) {
        this.code = code;
        this.message = message;
    }

    public int getCode() { return code; }
    public String getMessage() { return message; }
}

Unified Response Format

public class Response extends HashMap<String, Object> {
    public Response() {
        put("status", 200);
        put("message", "OK");
    }

    public static Response success() {
        return new Response();
    }

    public static Response success(Object data) {
        Response resp = new Response();
        resp.put("data", data);
        return resp;
    }

    public static Response fail(int code, String msg) {
        Response resp = new Response();
        resp.put("status", code);
        resp.put("message", msg);
        return resp;
    }

    public static Response fail(ErrorCode error) {
        return fail(error.getCode(), error.getMessage());
    }
}