How to validate request body in Spring Boot REST API?

Question

I'm building a REST API and need to validate the request body. I have a UserDTO class:

```java
public class UserDTO {
    private String email;
    private String name;
    private Integer age;
}
```

How do I validate that email is not null and is a valid email format, name is not blank, and age is between 18 and 100?

Also, how do I return proper error messages when validation fails?

boot_dev · Accepted Answer

Here's how to implement validation in Spring Boot:

**Step 1: Add dependency**
```xml

org.springframework.boot
    spring-boot-starter-validation

```

**Step 2: Annotate your DTO**
```java
public class UserDTO {
    @NotBlank(message = "Email is required")
    @Email(message = "Email should be valid")
    private String email;

@NotBlank(message = "Name is required")
    @Size(min = 2, max = 100, message = "Name must be between 2 and 100 characters")
    private String name;

@NotNull(message = "Age is required")
    @Min(value = 18, message = "Age must be at least 18")
    @Max(value = 100, message = "Age must not exceed 100")
    private Integer age;
}
```

**Step 3: Use @Valid in controller**
```java
@PostMapping("/users")
public ResponseEntity createUser(@Valid @RequestBody UserDTO userDTO) {
    // Process valid user
    return ResponseEntity.ok("User created");
}
```

**Step 4: Handle validation errors**
```java
@RestControllerAdvice
public class ValidationExceptionHandler {

@ExceptionHandler(MethodArgumentNotValidException.class)
    public ResponseEntity handleValidationErrors(
            MethodArgumentNotValidException ex) {

Map errors = new HashMap();
        ex.getBindingResult().getFieldErrors().forEach(error ->
            errors.put(error.getField(), error.getDefaultMessage())
        );

Map response = new HashMap();
        response.put("status", "error");
        response.put("errors", errors);

return ResponseEntity.badRequest().body(response);
    }
}
```

1 Answer