How to Handle Validation Exception in Spring Boot Correctly

In Spring Boot, handle validation exceptions by using @Valid on request objects and catching MethodArgumentNotValidException with an @ExceptionHandler method in a @ControllerAdvice class. This lets you return clear, custom error messages when validation fails.

Why This Happens

Validation exceptions occur when input data does not meet the rules defined by annotations like @NotNull or @Size. If you don't handle these exceptions, Spring Boot returns a default error response that may not be user-friendly.

java

import jakarta.validation.constraints.NotBlank;
import org.springframework.web.bind.annotation.PostMapping;
import org.springframework.web.bind.annotation.RequestBody;
import org.springframework.web.bind.annotation.RestController;

@RestController
public class UserController {

    @PostMapping("/users")
    public String createUser(@RequestBody User user) {
        return "User created";
    }
}

class User {
    @NotBlank(message = "Name is mandatory")
    private String name;

    // getters and setters
}

Output

HTTP 400 Bad Request with default error body, no clear validation message

The Fix

Add @Valid to the controller method parameter to trigger validation. Then create a @ControllerAdvice class with an @ExceptionHandler method to catch MethodArgumentNotValidException and return a custom error response.

java

import jakarta.validation.Valid;
import jakarta.validation.constraints.NotBlank;
import org.springframework.http.HttpStatus;
import org.springframework.http.ResponseEntity;
import org.springframework.validation.FieldError;
import org.springframework.web.bind.MethodArgumentNotValidException;
import org.springframework.web.bind.annotation.ControllerAdvice;
import org.springframework.web.bind.annotation.ExceptionHandler;
import org.springframework.web.bind.annotation.PostMapping;
import org.springframework.web.bind.annotation.RequestBody;
import org.springframework.web.bind.annotation.RestController;

import java.util.HashMap;
import java.util.Map;

@RestController
public class UserController {

    @PostMapping("/users")
    public String createUser(@Valid @RequestBody User user) {
        return "User created";
    }
}

class User {
    @NotBlank(message = "Name is mandatory")
    private String name;

    // getters and setters
}

@ControllerAdvice
class ValidationExceptionHandler {

    @ExceptionHandler(MethodArgumentNotValidException.class)
    public ResponseEntity<Map<String, String>> handleValidationExceptions(MethodArgumentNotValidException ex) {
        Map<String, String> errors = new HashMap<>();
        ex.getBindingResult().getAllErrors().forEach(error -> {
            String fieldName = ((FieldError) error).getField();
            String errorMessage = error.getDefaultMessage();
            errors.put(fieldName, errorMessage);
        });
        return new ResponseEntity<>(errors, HttpStatus.BAD_REQUEST);
    }
}

Output

HTTP 400 Bad Request with JSON body {"name":"Name is mandatory"} when name is blank

Prevention

Always use @Valid on input parameters that require validation. Centralize exception handling with @ControllerAdvice to keep controllers clean. Use meaningful validation messages and test validation rules early to avoid runtime errors.

Related Errors

Other common validation-related errors include:

• ConstraintViolationException: Happens with validation on method parameters outside controllers.
• BindException: Occurs when binding form data fails.
• HttpMessageNotReadableException: Happens if JSON is malformed.

Handle these similarly with @ExceptionHandler methods in @ControllerAdvice.

Key Takeaways

Use @Valid on controller method parameters to trigger validation.

Handle MethodArgumentNotValidException in a @ControllerAdvice class for custom error responses.

Provide clear validation messages with annotations like @NotBlank(message = "...").

Centralize exception handling to keep controllers simple and maintainable.

Test validation rules early to catch input errors before runtime.