How do you customize error messages for validation in Spring?

Table of Contents

• Introduction
• Customizing Error Messages with Validation Annotations
  • 1. Using the **message** Attribute in Annotations
    • Example: Custom Error Messages in Validation Annotations
  • 2. Using Property Files for Message Customization
    • Example: Customizing Validation Messages Using messages.properties
  • 3. Using **@Validated** for Grouped Validation with Custom Messages
    • Example: Grouped Validation with Custom Messages
• Handling Validation Errors Globally
  • 1. Global Exception Handler for Validation Errors
    • Example: Global Error Handling with Custom Messages
  • 2. Using Custom Error Objects
    • Example: Custom Error Response Object
• Conclusion

Introduction

When validating user inputs in Spring Boot applications, the default validation messages provided by annotations like @NotNull, @Size, and @Email might not always be clear or suitable for your users. Customizing error messages for validation helps make the responses more meaningful and user-friendly. In Spring Boot, this can be easily achieved by using the message attribute in validation annotations, along with exception handling for global error management.

In this guide, we will explore how to customize error messages in Spring Boot validation using annotations, properties files, and custom exception handling.

Customizing Error Messages with Validation Annotations

1. Using the **message** Attribute in Annotations

Spring’s validation annotations support the message attribute, which allows you to define custom error messages for specific validation failures. This message is displayed when the associated constraint is violated.

Example: Custom Error Messages in Validation Annotations

In this example, each field has a custom error message associated with it:

• For name, a custom message is displayed if the value is null or does not meet the size constraints.
• The email field uses a custom message for both null values and invalid email format.
• Similarly, the age field includes a custom message for null input.

These messages will be returned when the validation fails, instead of the default generic messages.

2. Using Property Files for Message Customization

Spring allows you to externalize validation messages by using properties files. This approach makes it easier to manage and localize error messages, especially for multi-language applications.

Example: Customizing Validation Messages Using messages.properties

You can define validation messages in a properties file (e.g., messages.properties), which Spring will load automatically.

Create a file named messages.properties under src/main/resources:

Then, use the **@NotNull** and **@Size** annotations in your model class without specifying the message attribute directly. Spring will automatically look up the messages in the properties file.

Spring Boot will automatically resolve these messages from the messages.properties file when validation fails.

3. Using **@Validated** for Grouped Validation with Custom Messages

If you need to validate certain fields under specific conditions (e.g., for different validation groups such as create and update operations), you can use grouped validation along with custom messages for each group.

Example: Grouped Validation with Custom Messages

In this case:

• CreateGroup and UpdateGroup are interfaces used to group validation constraints.
• The @NotNull and @Size annotations now include custom messages specific to the context of user creation.

You would use @Validated in the controller to apply the correct validation group.

Handling Validation Errors Globally

To ensure that custom validation messages are returned in a user-friendly format, you can use a global exception handler to handle validation errors and customize the response.

1. Global Exception Handler for Validation Errors

Use the @RestControllerAdvice annotation to create a global exception handler that intercepts validation errors.

Example: Global Error Handling with Custom Messages

In this example:

• If a validation error occurs, the handleValidationExceptions method captures the error.
• The error message is extracted using error.getDefaultMessage() and a custom message is returned in the response body.

2. Using Custom Error Objects

You can also use custom error response objects instead of just returning a list of error messages.

Example: Custom Error Response Object

Here, the ErrorResponse class contains a field and a message, and the handler returns a structured list of error responses in the 400 Bad Request response.

Conclusion

Customizing error messages in Spring Boot for validation is an essential practice to improve the user experience. You can achieve this by:

1. Using the **message** attribute in validation annotations like @NotNull, @Size, and @Email for custom error messages.
2. Externalizing error messages using property files for better maintainability and localization.
3. Implementing grouped validation with custom messages to handle different contexts, such as create and update.
4. Handling validation errors globally by using exception handlers to provide structured and user-friendly error responses.

By leveraging these techniques, you can ensure that your Spring Boot application provides clear, understandable validation feedback to users, improving both usability and error management.