Validation

Bean Validation (JSR 380) provides a standard way to validate data using annotations.

Basic Validation Annotations

public class CreateUserRequest {

    @NotBlank(message = "Name is required")
    @Size(min = 2, max = 100, message = "Name must be 2-100 characters")
    private String name;

    @NotBlank(message = "Email is required")
    @Email(message = "Email must be valid")
    private String email;

    @NotNull(message = "Age is required")
    @Min(value = 18, message = "Must be at least 18")
    @Max(value = 120, message = "Must be at most 120")
    private Integer age;

    @NotBlank(message = "Password is required")
    @Size(min = 8, message = "Password must be at least 8 characters")
    @Pattern(regexp = "^(?=.*[a-z])(?=.*[A-Z])(?=.*\\d).*$",
             message = "Password must contain uppercase, lowercase, and digit")
    private String password;
}

Common Annotations

Annotation	Validates
@NotNull	Not null
@NotBlank	Not null and not empty string
@NotEmpty	Not null and not empty collection/string
@Size(min, max)	String/collection length
@Min(value)	Minimum numeric value
@Max(value)	Maximum numeric value
@Email	Valid email format
@Pattern(regex)	Matches regex pattern
@Positive	Must be positive
@PositiveOrZero	Must be >= 0
@Past	Must be in the past
@Future	Must be in the future

Enabling Validation

@RestController
@RequestMapping("/api/users")
public class UserController {

    // @Valid triggers validation
    @PostMapping
    public ResponseEntity<UserDto> createUser(@Valid @RequestBody CreateUserRequest request) {
        return ResponseEntity.status(HttpStatus.CREATED)
            .body(userService.createUser(request));
    }
}

Validation Layers

1. Client-side: Immediate feedback
2. API Gateway: Basic validation
3. Service: Business rules
4. Database: Constraints

Types

• Type checking
• Format validation (email, phone)
• Range checking
• Length limits
• Business rules

Best Practices

• Validate on server (never trust client)
• Return specific error messages
• Use whitelist approach
• Log validation failures

Key Points

• Understanding Validation is essential for production systems
• Always consider scalability and maintainability
• Test thoroughly before deploying to production
• Monitor performance and set up alerting

Common Patterns

1. Validation: Always validate input at the boundary
2. Error Handling: Use structured error responses
3. Logging: Log key events for debugging
4. Testing: Unit, integration, and load tests
5. Documentation: Keep docs updated with code changes