Spring Boot Validation Tutorial with Real Examples
Introduction
Data validation is an essential part of every application. Without proper validation, users can submit invalid, incomplete, or malicious data that may cause application errors and database inconsistencies.
Spring Boot provides built-in validation support using Jakarta Bean Validation. By applying validation annotations, developers can ensure that incoming data meets specific requirements before processing it.
In this tutorial, you'll learn how to validate request data in Spring Boot using practical examples.
What is Validation?
Validation is the process of checking whether input data satisfies predefined rules.
Examples:
✅ Name should not be empty
✅ Email should be valid
✅ Password should have a minimum length
✅ Age should be positive
Without validation:
{ "name":"", "email":"abc", "age":-10 }
This data should not be accepted by the application.
Why Validation is Important
Validation helps:
- Improve data quality
- Prevent invalid database records
- Improve API reliability
- Improve user experience
- Enhance security
Add Validation Dependency
Add the following dependency to your pom.xml:
<dependency> <groupId>org.springframework.boot</groupId> <artifactId>spring-boot-starter-validation</artifactId> </dependency>
This dependency enables Jakarta Bean Validation support.
Create EmployeeDTO
Validation should usually be applied to DTO classes.
public class EmployeeDTO { @NotBlank(message = "Name is required") private String name; @Email(message = "Invalid email format") private String email; @NotBlank(message = "Department is required") private String department; }
Understanding Validation Annotations
@NotBlank
Used for String values.
@NotBlank(message = "Name is required") private String name;
Rejects:
null "" " "
@NotNull
Used when a field cannot be null.
@NotNull private Long employeeId;
Validates email addresses.
@Email(message = "Invalid email") private String email;
Valid:
john@example.com
Invalid:
john john@
@Size
Controls minimum and maximum length.
@Size( min = 3, max = 50, message = "Name must be between 3 and 50 characters") private String name;
@Min
Minimum numeric value.
@Min( value = 18, message = "Age must be at least 18") private int age;
@Max
Maximum numeric value.
@Max( value = 60, message = "Age cannot exceed 60") private int age;
Enable Validation in Controller
Use @Valid before the request body.
@PostMapping public Employee createEmployee( @Valid @RequestBody EmployeeDTO employeeDTO) { return service.save(employeeDTO); }
When invalid data is submitted, Spring automatically triggers validation.
Valid Request Example
{ "name":"Muhammad Zeeshan", "email":"zeeshan@example.com", "department":"IT" }
Invalid Request Example
{ "name":"", "email":"invalid", "department":"" }
Validation Error Response
{ "timestamp":"2026-07-24", "status":400, "errors":[ "Name is required", "Invalid email format", "Department is required" ] }
Global Validation Exception Handling
Create:
GlobalExceptionHandler.java
@RestControllerAdvice public class GlobalExceptionHandler { @ExceptionHandler( MethodArgumentNotValidException.class) public ResponseEntity<Map<String,String>> handleValidationExceptions( MethodArgumentNotValidException ex) { Map<String,String> errors = new HashMap<>(); ex.getBindingResult() .getFieldErrors() .forEach(error -> errors.put( error.getField(), error.getDefaultMessage())); return ResponseEntity .badRequest() .body(errors); } }
Sample Validation Response
{ "name":"Name is required", "email":"Invalid email format" }
This makes API responses much cleaner and easier to understand.
Custom Validation Example
Sometimes built-in annotations are not enough.
Example:
Company emails only.
Allowed: john@company.com Rejected: john@gmail.com
This can be implemented using a custom validator.
Validation Flow Diagram
Client Request ↓ Controller ↓ @Valid ↓ Validation Rules ↓ Valid Data? ↙ ↘ Yes No ↓ ↓ Service Error Response ↓ Database
Best Practices
Validate DTOs
Avoid validating Entity classes directly.
Use Meaningful Messages
Good:
@NotBlank( message="Name is required")
Bad:
@NotBlank
Centralize Exception Handling
Use:
@RestControllerAdvice
Keep Validation Close to Input
Validate requests before business logic executes.
Common Mistakes
Forgetting @Valid
Without:
@Valid
Validation will not execute.
Using Validation on Entity Only
Prefer DTO validation.
Ignoring Error Responses
Always return meaningful validation messages.
Interview Questions
What is Bean Validation?
Bean Validation is a specification used to validate Java objects using annotations.
What is @Valid?
@Valid triggers validation before processing a request.
Difference Between @NotNull and @NotBlank?
@NotNull:
Rejects null
@NotBlank:
Rejects null Rejects "" Rejects whitespace
What is MethodArgumentNotValidException?
It is thrown when request validation fails.
FAQ
Does Spring Boot support validation out of the box?
Yes, after adding the validation dependency.
Can validation be applied to REST APIs?
Yes, it is commonly used in REST APIs.
Can I create custom validation annotations?
Yes.
Should validation be done in DTOs or Entities?
DTOs are generally recommended.