Map<String, List<User>> usersByCountry = new HashMap<>(); for (User user : listOfUsers) { List<User> users = usersByCountry.get(user.getCountry()); if (users == null) { users = new ArrayList<>(); usersByCountry.put(user.getCountry(), users); } users.add(user); }
Map<String, List<User>> usersByCountry = new HashMap<>(); for (User user : listOfUsers) { usersByCountry.computeIfAbsent(user.getCountry(), v -> new ArrayList<>()).add(user); }
Map<String, List<User>> usersByCountry = new HashMap<String, List<User>>(); for(User user : listOfUsers) { List<User> users = usersByCountry.get(user.getCountry()); if (users == null) { usersByCountry.put(user.getCountry(), users = new ArrayList<User>()); } users.add(user); }
public class UserValidator implements Validator { public boolean supports(Class clazz) { return clazz.isAssignableFrom(User.class); } public void validate(Object command, Errors errors) { User user = (User) command; if(user.getOccupation() == null) errors.rejectValue("occupation", "errors.required", null); if(user.getCountry() == null) errors.rejectValue("country", "errors.required", null); } }