Validating nested objects and collections.

1. Nested Objects:

Use @Valid on the nested object field inside your DTO.

public class UserDTO {
    @Valid
    private AddressDTO address;
}

2. Collections:

To validate a list of objects, you can use @Valid as well:

public void saveUsers(@RequestBody @Valid List<UserDTO> users) { ... }

Note: For method-level validation of collections, you often need @Validated on the Class level.