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PavanButke
PavanButke

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Mastering Custom Validation in Spring Boot: A Step-by-Step Guide

Introduction:

  • Brief overview of validation in Spring Boot.

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  • Importance of custom validation for specific business requirements.
  • Introduction to the example scenario involving FinancialProjectDto and the need for custom validation.

Section 1: Setting the Stage

  • Explanation of the example scenario: Financial Project Budgeting with the FinancialProjectDto.
  • Overview of the DTO structure and the significance of accurate data entry.
  • Discuss the limitations of standard validation annotations.

Section 2: Creating Custom Validation Annotation

  • In-depth walkthrough of creating a custom validation annotation (BudgetCodeConstraint).
  • Explanation of the motivation behind a custom annotation for budgetCode.
  • Code snippet:


// BudgetCodeConstraint.java
@Target({ElementType.FIELD, ElementType.METHOD})
@Retention(RetentionPolicy.RUNTIME)
@Constraint(validatedBy = BudgetCodeValidator.class)
public @interface BudgetCodeConstraint {
    String message() default "Budget code must have less than 5 digits";
    Class<?>[] groups() default {};
    Class<? extends Payload>[] payload() default {};
    Class<?>[] customValidationGroups() default {};
}


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Section 3: Crafting a Custom Validator

  • Step-by-step guide on implementing a custom validator (BudgetCodeValidator).
  • Explanation of the ConstraintValidator interface and its role.
  • Code snippet:


// BudgetCodeValidator.java
public class BudgetCodeValidator implements ConstraintValidator<BudgetCodeConstraint, String> {
    @Override
    public void initialize(BudgetCodeConstraint constraintAnnotation) {
    }

    @Override
    public boolean isValid(String budgetCode, ConstraintValidatorContext context) {
        return budgetCode == null || budgetCode.length() < 5;
    }
}


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Section 4: Using Validation Groups

  • Introduction to validation groups and their significance.
  • Creation of a custom validation group (BudgetCustomValidationGroup).
  • Application of the custom validation group to the DTO (FinancialProjectDto).
  • Code snippet:


// BudgetCustomValidationGroup.java
public interface BudgetCustomValidationGroup {
}

// FinancialProjectDto.java
@BudgetCodeConstraint(customValidationGroups = BudgetCustomValidationGroup.class)
public class FinancialProjectDto {
    // Fields and methods...
}


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Section 5: Integrating with Spring Boot

  • Explanation of how Spring Boot integrates with validation.
  • Annotation of the controller method with @Validated.
  • Handling validation errors with BindingResult.
  • Code snippet:


// FinancialProjectController.java
@PostMapping("/financialProjectEndpoint")
public ResponseEntity<?> financialProjectControllerMethod(@Validated(BudgetCustomValidationGroup.class) @RequestBody FinancialProjectDto financialProjectDto, BindingResult bindingResult) {
    if (bindingResult.hasErrors()) {
        // Handle validation errors
        return ResponseEntity.badRequest().body("Validation failed");
    }

    // Your controller logic for a valid DTO
    return ResponseEntity.ok("DTO is valid");
}


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Section 6: Troubleshooting and Best Practices

  • Common issues faced during custom validation and their solutions.
  • Best practices for organizing custom validation code and packages.
  • Tips for handling complex validation scenarios.

Section 7: Real-World Analogies

  • Drawing analogies between custom validation in software and real-world scenarios.
  • Making comparisons with everyday situations to enhance understanding.
  • Example analogies to illustrate the importance and impact of validation in various contexts.

Section 8: Postman Response and Sample Body

  • Include a section with a sample Postman-generated response and a sample request body.
  • Provide a step-by-step guide on how to use Postman to test the custom validation.
  • Example Response:


{
    "status": "Bad Request",
    "message": "Validation failed",
    "errors": [
        {
            "field": "budgetCode",
            "message": "Budget code must have less than 5 digits"
        },
        // Other validation errors...
    ]
}


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  • Example Request Body:


{
"budgetCode": "123456", // This should trigger validation error
// Other fields...
}
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Revise:

  • Recap of the importance of custom validation in Spring Boot.
  • Encouragement for developers to tailor validation to their specific needs.
  • Acknowledgment of the enhanced readability and maintainability achieved through custom validation.

Additional Resources:

  1. - https://www.google.com/amp/s/blog.tericcabrel.com/write-custom-validator-for-body-request-in-spring-boot/amp/
  2. - https://docs.jboss.org/hibernate/validator/5.1/reference/en-US/html/validator-customconstraints.html

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