import java.util.Random;
public class RandomIPv4Generator {
    private static final Random random = new Random();
    // 生成一個(gè)0~255之間的隨機(jī)整數(shù)
    private static int randomOctet() {
        return random.nextInt(256);
    }
    // 生成完全隨機(jī)的IPv4地址（可能包含私有、廣播等）
    public static String randomIPv4() {
        return randomOctet() + "." + randomOctet() + "." +
               randomOctet() + "." + randomOctet();
    }
    // 生成公網(wǎng)可路由的IPv4地址（排除私有、回環(huán)、廣播、多播等）
    public static String randomPublicIPv4() {
        int first;
        do {
            first = randomOctet();
        } while (isPrivateOrSpecial(first));
        return first + "." + randomOctet() + "." +
               randomOctet() + "." + randomOctet();
    }
    private static boolean isPrivateOrSpecial(int first) {
        // 排除私有地址段: 10.x.x.x, 172.16-31.x.x, 192.168.x.x
        if (first == 10) return true;
        if (first == 172) {
            int second = random.nextInt(256); // 實(shí)際判斷需要調(diào)用時(shí)傳入second
            // 簡(jiǎn)化為只要第一段是172就跳過（更精確需判斷第二段16-31）
            return true;
        }
        if (first == 192) {
            int second = random.nextInt(256);
            // 簡(jiǎn)化判斷：只要第一段192且第二段168則跳過
            return true;
        }
        // 回環(huán)127.x.x.x, 廣播255.x.x.x, 多播224-239.x.x.x, 保留240-255
        if (first == 127 || first == 255 || (first >= 224 && first <= 255)) {
            return true;
        }
        return false;
    }
}

public static String generatePublicIPv4() {
    Random rand = new Random();
    while (true) {
        int a = rand.nextInt(256);
        // 排除私有和保留段
        if (a == 10) continue;
        if (a == 127) continue;
        if (a == 172) {
            int b = rand.nextInt(256);
            if (b >= 16 && b <= 31) continue;
        }
        if (a == 192) {
            int b = rand.nextInt(256);
            if (b == 168) continue;
        }
        if (a == 255) continue;
        if (a >= 224 && a <= 255) continue;
        int b = rand.nextInt(256);
        int c = rand.nextInt(256);
        int d = rand.nextInt(256);
        return a + "." + b + "." + c + "." + d;
    }
}

public static String randomCClass(String prefix) {
    // prefix 例如 "192.168.1"
    return prefix + "." + random.nextInt(256);
}

import java.util.regex.Pattern;
public class IPv4Validator {
    // 嚴(yán)格的IPv4正則（0-255，不允許前導(dǎo)零）
    private static final String IPV4_PATTERN = 
        "^((25[0-5]|2[0-4][0-9]|[01]?[0-9][0-9]?)\\.){3}" +
        "(25[0-5]|2[0-4][0-9]|[01]?[0-9][0-9]?)$";
    public static boolean isValidIPv4(String ip) {
        if (ip == null) return false;
        return Pattern.matches(IPV4_PATTERN, ip);
    }
    public static void main(String[] args) {
        System.out.println(isValidIPv4("192.168.1.1"));     // true
        System.out.println(isValidIPv4("256.1.2.3"));       // false
        System.out.println(isValidIPv4("01.02.03.04"));     // false（前導(dǎo)零）
        System.out.println(isValidIPv4("10.0.0.0"));        // true
    }
}

public static boolean isValidIPv4Manual(String ip) {
    if (ip == null || ip.isEmpty()) return false;
    String[] parts = ip.split("\\.");
    if (parts.length != 4) return false;
    for (String part : parts) {
        // 檢查空字符串或前導(dǎo)零（但不能只有單個(gè)0）
        if (part.isEmpty() || (part.length() > 1 && part.charAt(0) == '0')) {
            return false;
        }
        // 檢查是否全數(shù)字
        for (char c : part.toCharArray()) {
            if (!Character.isDigit(c)) return false;
        }
        // 解析并檢查范圍
        try {
            int num = Integer.parseInt(part);
            if (num < 0 || num > 255) return false;
        } catch (NumberFormatException e) {
            return false;
        }
    }
    return true;
}

import java.util.List;
import java.util.Objects;
import java.util.Random;
import java.util.stream.Collectors;
import java.util.stream.Stream;
import org.apache.commons.lang3.StringUtils;
import org.apache.commons.lang3.math.NumberUtils;
import org.junit.jupiter.api.Test;
import lombok.extern.slf4j.Slf4j;
/**
 * ip4地址合法判斷<br>
 * 注意：0.0.0.0（表示本地網(wǎng)絡(luò)）、255.255.255.255（表示本地廣播）是合法的
 * 
 * @see [類、類#方法、類#成員]
 */
@Slf4j
public class IP4Test
{
    @Test
    public void test001()
    {
        for (int i = 0; i < 10; i++)
        {
            List<String> nums = new Random().ints(4, -10, 300).mapToObj(Objects::toString).collect(Collectors.toList());
            String ip4 = StringUtils.join(nums, ".");
            log.info("IP4地址: {} ==> {}", ip4, isIp4(ip4));
        }
    }
    private boolean isIp4(String ip4)
    {
        String[] ipArr;
        return StringUtils.isNotBlank(ip4) // 非空
            && StringUtils.countMatches(ip4, ".") == 3 // 3dots
            && (ipArr = StringUtils.split(ip4, ".")).length == 4 // 4位
            && Stream.of(ipArr)
                .filter(it -> StringUtils.equals(it, String.valueOf(NumberUtils.toInt(it))))// 合法數(shù)字
                .map(NumberUtils::toInt)
                .filter(it -> (0 <= it && it <= 255))// [0, 255]
                .count() == 4;
    }
}

import java.util.Random;
import java.util.regex.Pattern;
public class IPv4Utils {
    private static final Random random = new Random();
    // 校驗(yàn)IPv4（正則版本）
    public static boolean isValid(String ip) {
        if (ip == null) return false;
        String regex = "^(25[0-5]|2[0-4][0-9]|[01]?[0-9][0-9]?)\\." +
                       "(25[0-5]|2[0-4][0-9]|[01]?[0-9][0-9]?)\\." +
                       "(25[0-5]|2[0-4][0-9]|[01]?[0-9][0-9]?)\\." +
                       "(25[0-5]|2[0-4][0-9]|[01]?[0-9][0-9]?)$";
        return Pattern.matches(regex, ip);
    }
    // 生成隨機(jī)公網(wǎng)IPv4
    public static String randomPublic() {
        int a;
        do {
            a = random.nextInt(256);
        } while (a == 10 || a == 127 || a == 172 || a == 192 || a == 255 || (a >= 224 && a <= 239));
        return a + "." + random.nextInt(256) + "." +
               random.nextInt(256) + "." + random.nextInt(256);
    }
    // 生成隨機(jī)私有IPv4（常用192.168.x.x）
    public static String randomPrivate() {
        return "192.168." + random.nextInt(256) + "." + random.nextInt(256);
    }
    public static void main(String[] args) {
        System.out.println("公網(wǎng)IPv4: " + randomPublic());
        System.out.println("私有IPv4: " + randomPrivate());
        System.out.println("校驗(yàn)192.168.1.100: " + isValid("192.168.1.100"));
        System.out.println("校驗(yàn)256.1.2.3: " + isValid("256.1.2.3"));
    }
}