Java 17: Difficulty with Custom `@RequestBody` Validation in Spring MVC using Hibernate Validator
I need help solving I'm following best practices but I've been struggling with this for a few days now and could really use some help... Quick question that's been bugging me - I'm working with an scenario with custom validation when using `@RequestBody` in my Spring MVC application. I have a DTO class that I want to validate with Hibernate Validator annotations, but it seems like the validation is not being triggered when the request body is malformed or missing required fields. I have the following DTO: ```java import javax.validation.constraints.NotBlank; import javax.validation.constraints.Size; public class UserDTO { @NotBlank(message = "Username must not be blank") private String username; @NotBlank(message = "Email must not be blank") private String email; @Size(min = 8, message = "Password must be at least 8 characters") private String password; // Getters and Setters } ``` And here’s my controller method: ```java import org.springframework.http.HttpStatus; import org.springframework.http.ResponseEntity; import org.springframework.web.bind.annotation.*; import javax.validation.Valid; @RestController @RequestMapping("/api/users") public class UserController { @PostMapping public ResponseEntity<String> createUser(@Valid @RequestBody UserDTO userDTO) { // Logic to save user return ResponseEntity.status(HttpStatus.CREATED).body("User created successfully"); } } ``` I expected that if the `username` or `email` fields are blank, or if the `password` is shorter than 8 characters, Spring would return a 400 Bad Request with the appropriate validation messages. However, when I send a request with an empty JSON body (`{}`) or invalid data, I receive a 500 Internal Server behavior with the following stack trace: ``` org.springframework.http.converter.HttpMessageNotReadableException: JSON parse behavior: want to deserialize value of type `java.lang.String` from Object value (token `JsonToken.START_OBJECT`) at [Source: (org.springframework.http.converter.json.MappingJackson2HttpMessageConverter); line: 1, column: 1] (through reference chain: UserDTO["username"]) ``` I’ve checked that I have the necessary dependencies for Hibernate Validator in my `pom.xml`: ```xml <dependency> <groupId>org.springframework.boot</groupId> <artifactId>spring-boot-starter-validation</artifactId> </dependency> ``` I’ve also enabled validation globally in my Spring configuration, yet it seems that the annotations on the DTO are being ignored. Is there something I'm missing in the configuration, or is there a specific way to handle validation with `@RequestBody` that I need to follow? Any help would be greatly appreciated! My development environment is Windows. Am I missing something obvious? I'm working in a CentOS environment. Hoping someone can shed some light on this. What would be the recommended way to handle this? The project is a desktop app built with Java.