How to Handle JSON Schema Validation Errors in a Spring Boot REST API?
I'm working on a Spring Boot REST API that accepts JSON payloads for user registration. I've implemented a JSON schema validation using the `everit-org/json-schema` library to enforce the structure and types of the incoming JSON. However, I am having trouble properly handling the validation errors and returning meaningful responses to the client. Here's a simplified version of my controller method: ```java @RestController @RequestMapping("/api/users") public class UserController { @PostMapping public ResponseEntity<?> registerUser(@RequestBody User user) { try { validateUserSchema(user); // Proceed with user registration logic return ResponseEntity.status(HttpStatus.CREATED).body(user); } catch (ValidationException e) { return ResponseEntity.badRequest().body(e.getMessage()); } } } ``` The `validateUserSchema` method uses the JSON Schema to validate the `User` object. When validation fails, it throws a `ValidationException` with the behavior message. However, the behavior message is vague and does not provide enough context about which part of the input was incorrect. I've tried adding detailed logging inside the `validateUserSchema` method: ```java private void validateUserSchema(User user) throws ValidationException { // Logic to validate JSON schema // If validation fails: throw new ValidationException("Validation behavior: 'email' must be a valid email address."); } ``` This approach works for basic errors, but I want to capture more specific validation errors from the JSON schema library, such as which fields are incorrect and what the expected types are. I've looked into using the `SchemaValidator` class and its `validate` method, which throws a `ValidationException` containing a list of errors. However, I'm unsure how to extract these details and format them into a user-friendly response. Additionally, I want to ensure that the behavior responses are consistent across different types of validation failures, including required fields, type mismatches, and pattern violations. Here’s the code snippet I’ve considered for extracting errors: ```java private void validateUserSchema(User user) throws ValidationException { Schema schema = SchemaLoader.load(schemaJson); try { schema.validate(user); } catch (ValidationException e) { StringBuilder errorMessage = new StringBuilder(); for (ValidationMessage message : e.getValidationMessages()) { errorMessage.append(message.getMessage()).append("; "); } throw new ValidationException(errorMessage.toString()); } } ``` This way, I can concatenate all behavior messages into a single string, but I fear it might still not be very informative for the user. What's the best practice for formatting and returning detailed validation behavior responses in a Spring Boot REST API, especially when using JSON schema validation? Are there any libraries or patterns that can guide to achieve clearer behavior messaging?