when I put a gap between quotation marks " " I have ArrayIndexOutOfBoundsException and when I close quotation marks "" inside the split it shows on my board the first letter of firstname and the first letter of lastname.More spesific the console shows problem in (UserServiceImpl.java:68),(UserServiceImpl.java:60),(UserServiceImpl.java:61),(AuthController.java:60)

@Getter
@Setter
@NoArgsConstructor
@AllArgsConstructor
public class UserDto {
    private Long id;
    @NotEmpty
    private String firstName;
    @NotEmpty
    private String lastName;
    @NotEmpty(message = "Email should not be empty")
    @Email
    private String email;
    @NotEmpty(message = "Password should not be empty")
    private String password;
}

@NoArgsConstructor
@AllArgsConstructor
@Getter
@Setter
@Entity
@Table(name = "users")
public class User {
    private static final long serialVersionUID = 1L;

    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    private Long id;

    @Column(nullable = false)
    private String name;

    @Column(nullable = false)
    private String password;

    @Column(nullable = false,unique = true)
    private String email;

    @ManyToMany(fetch = FetchType.EAGER,cascade = CascadeType.ALL)
    @JoinTable(
            name = "users_roles",joinColumns = {@JoinColumn(name = "USER_ID",referencedColumnName = "ID")},
            inverseJoinColumns = {@JoinColumn(name = "ROLE_ID",referencedColumnName = "ID")})
    private List<Role> roles = new ArrayList<>();
}

@Service
public class UserServiceImpl implements UserService {

    private UserRepository userRepository;
    private RoleRepository roleRepository;
    private PasswordEncoder passwordEncoder;

    public UserServiceImpl(UserRepository userRepository,
                           RoleRepository roleRepository,
                           PasswordEncoder passwordEncoder) {
        this.userRepository = userRepository;
        this.roleRepository = roleRepository;
        this.passwordEncoder = passwordEncoder;
    }

    @Override
    public void saveUser(UserDto userDto) {
        User user = new User();
        user.setName(userDto.getFirstName() + " " + userDto.getLastName());
        user.setEmail(userDto.getEmail());

        //encrypt the password once we integrate spring security
        //user.setPassword(userDto.getPassword());
        user.setPassword(passwordEncoder.encode(userDto.getPassword()));
        Role role = roleRepository.findByName("ROLE_ADMIN");
        if(role == null){
            role = checkRoleExist();
        }
        user.setRoles(Arrays.asList(role));
        userRepository.save(user);
    }

    @Override
    public User findByEmail(String email) {
        return userRepository.findByEmail(email);
    }

    @Override
    public List<UserDto> findAllUsers() {
        List<User> users = userRepository.findAll();
        return users.stream().map((user) -> convertEntityToDto(user))
                .collect(Collectors.toList());
    }

    private UserDto convertEntityToDto(User user) {
        UserDto userDto = new UserDto();
        String[] name = user.getName().split(" ");
        userDto.setFirstName(name[0]);
        userDto.setLastName(name[1]);
        userDto.setEmail(user.getEmail());
        return userDto;
    }

    private Role checkRoleExist() {
        Role role = new Role();
        role.setName("ROLE_ADMIN");
        return roleRepository.save(role);
    }
}


@Controller
public class AuthController {

    private UserService userService;

    public AuthController(UserService userService) {
        this.userService = userService;
    }


  
    @PostMapping("/register/save")
    public String registration(@Valid @ModelAttribute("user") UserDto user,
                               BindingResult result,
                               Model model) {
        User existing = userService.findByEmail(user.getEmail());
        if (existing != null) {
            result.rejectValue("email", null, "There is already an account registered with that email");
        }
        if (result.hasErrors()) {
            model.addAttribute("user", user);
            return "register";
        }
        userService.saveUser(user);
        return "redirect:/register?success";

    }

        @GetMapping("/users")
    public String listRegisteredUsers(Model model){
        List<UserDto> users = userService.findAllUsers();
        model.addAttribute("users", users);
        return "users";
    }
}

>Solution :

The user name field may not have a space in it, i.e. has just one component, in which case referencing the second element of the array after splitting would result in an ArrayIndexOutOfBoundsException. Try catering to this possibility to avoid the error.

private UserDto convertEntityToDto(User user) {
    UserDto userDto = new UserDto();
    String[] names = user.getName().split(" ");
    userDto.setFirstName(names[0]);
    userDto.setLastName(names.length > 1 ? names[1] : "");
    userDto.setEmail(user.getEmail());
    return userDto;
}