IpValidator.java

package com.acidtango.javaboilerplate;

import org.jetbrains.annotations.Contract;
import org.jetbrains.annotations.NotNull;

import java.util.Arrays;
import java.util.Optional;
import java.util.function.Predicate;

public class IpValidator {
    @NotNull
    @Contract(pure = true)
    private static Optional<Integer> parseInt (@NotNull String number) {
        try {
            Integer parsedNumber = Integer.parseInt(number);
            if (parsedNumber.toString().length() != number.length()) {
                return Optional.empty();
            }
            return Optional.of(parsedNumber);
        } catch(NumberFormatException | NullPointerException e) {
            return Optional.empty();
        }
    }

    @NotNull
    @Contract(pure = true)
    private static Predicate<Integer> isLessOrEqualThan(@NotNull Integer b) {
        return a -> a <= b;
    }

    @NotNull
    @Contract(pure = true)
    private static Predicate<Integer> isGreaterOrEqualThan(@NotNull Integer b) {
        return a -> a >= b;
    }

    @NotNull
    @Contract(pure = true)
    public static Boolean isValid(@NotNull String ip) {
        var validDigitsCount = Arrays.stream(ip.split("\\."))
                .map(IpValidator::parseInt)
                .filter(Optional::isPresent)
                .map(Optional::get)
                .filter(isLessOrEqualThan(255))
                .filter(isGreaterOrEqualThan(0))
                .count();

        return validDigitsCount == 4;
    }
}