Spring Boot application data validation

In a Spring Boot application, data validation can be handled by using the Bean Validation API (JSR-303 and JSR-349) which is included in the Java standard library.Spring provides support for Bean Validation through the spring-context-support module, which allows you to easily apply validation rules to your data by annotating the fields of your Java beans with validation constraints.

Here’s an example of how you might use Bean Validation to validate the data of a form:

public class UserForm {

    @NotNull
    @Size(min = 3, max = 20)
    private String name;

    @NotNull
    @Email
    private String email;

    @NotNull
    @Min(18)
    private Integer age;

    // getters and setters
}

In this example, the name, email, and age fields are annotated with validation constraints. The @NotNull annotation indicates that the field cannot be null, the @Size annotation indicates that the field must be between 3 and 20 characters, the @Email annotation that the field must be a valid email address and the @Min annotation that the age must be greater than or equal to 18.

To validate the data, you can use the Validator interface provided by the Bean Validation API. Here’s an example of how you might use the Validator to validate the data of a form:

@Service
public class UserService {

    private final Validator validator;

    public UserService(Validator validator) {
        this.validator = validator;
    }

    public void createUser(UserForm form) {
        Set<ConstraintViolation<UserForm>> violations = validator.validate(form);
        if (!violations.isEmpty()) {
            // handle violations
        }
    }
}

In this example, the createUser method uses the validator to validate the data of the UserForm and checks if there are any violations. If there are violations, the method can handle them by throwing an exception or returning an error message.

Spring Boot also provides support for data validation through the use of the spring-boot-starter-validation dependency which automatically configures the application with Hibernate Validator, the reference implementation of the Bean Validation API.

Additionally, you can also use JSR-380 (Bean Validation 2.0) which is a more recent version of Bean Validation API that provides additional functionality such as method level validation,

cross-parameter validation and the ability to execute custom validation logic.

Another way to handle data validation in a Spring Boot application is by using the @Valid annotation on method parameters. For example, in a REST controller:

@PostMapping("/users")
public ResponseEntity<User> createUser(@Valid @RequestBody UserForm form) {
  // Your code here
}

This will automatically validate the UserForm object using the constraints defined in its class before the request is handled.

Spring also provides a way to customize the error message of validation through message attribute of validation annotation and also MessageSource for internationalization.

In summary, Spring Boot provides several ways to handle data validation in a Spring Boot application, such as using the Bean Validation API and the @Valid annotation on method parameters. You can also customize the error message of validation through message attribute of validation annotation and also MessageSource for internationalization.