Enabling Startup Parameter Validation in Spring Boot Using Java Validation

When a Spring Boot project relies on configuration parameters, missing values often cause runtime exceptions only when a component is used. By enabling Java Validation on configuration properties, you can validate these parameters during application startup and fail fast if they are absent or incorrect.

To activate startup validation, annotate your @ConfigurationProperties class with @Validated (along with Lombok's @Data and Spring's @Component ) and add constraint annotations such as @NotEmpty(message="Configuration must contain [app.id]") to the fields that need validation:

@Validated
@Data
@ConfigurationProperties(prefix = "app")
@Component
public class AppConfigProperties {
    @NotEmpty(message = "配置文件配置必须要配置[app.id]属性")
    private String id;
}

This configuration causes Spring to verify that application.yml contains the app.id entry; if it is missing, the application fails to start with a validation exception.

Note that the validation works only with @ConfigurationProperties ; the @Value annotation does not support this feature.

Inject the validated properties wherever needed:

@Autowired
private AppConfigProperties appConfigProperties;

The framework supports a wide range of Bean Validation constraints, for example:

Constraint

Description

@Null

Value must be null

@NotNull

Value must not be null

@AssertFalse

Value must be false

@AssertTrue

Value must be true

@DecimalMax(value)

Numeric value must be less than or equal to the specified maximum

@DecimalMin(value)

Numeric value must be greater than or equal to the specified minimum

@Digits(integer,fraction)

Numeric value must have at most

integer

digits in the integer part and

fraction

digits in the fractional part

@Future

Value must be a future date

@Max(value)

Numeric value must be less than or equal to the specified maximum

@Min(value)

Numeric value must be greater than or equal to the specified minimum

@Past

Value must be a past date

@Pattern(value)

Value must match the given regular expression

@Size(min,max)

String or collection size must be between

min

and

max

@NotEmpty

Value must not be null and must contain at least one element (for strings, length > 0)

@NotBlank

String must contain at least one non‑whitespace character

@Email

Value must be a well‑formed email address

If the built‑in constraints are insufficient, you can create custom validation logic by implementing org.springframework.validation.Validator :

public class ConfigPropertiesValidator implements Validator {
    @Override
    public boolean supports(Class
clazz) {
        return AppConfigProperties.class.isAssignableFrom(clazz);
    }

    @Override
    public void validate(Object target, Errors errors) {
        AppConfigProperties config = (AppConfigProperties) target;
        if (StringUtils.isEmpty(config.getId())) {
            errors.rejectValue("id", "app.id.empty", "[app.id] property must be configured");
        } else if (config.getId().length() < 5) {
            errors.rejectValue("id", "app.id.short", "[app.id] length must be at least 5");
        }
    }
}

Register the validator as a bean with the exact name configurationPropertiesValidator so that Spring Boot picks it up during startup:

@Bean
public ConfigPropertiesValidator configurationPropertiesValidator() {
    return new ConfigPropertiesValidator();
}

After adjusting the app.id value in application.yml , you will see either a successful start or the custom error messages defined above.

Summary : Enabling Spring Boot's startup validation using Java Validation annotations and optional custom validators allows early detection of mis‑configured parameters, reduces debugging effort, and provides a solid foundation for building reusable starter libraries that enforce required configuration such as a Redis key prefix.