确保Java中URL的有效性和可连接性：高级验证策略

import java.net.InetSocketAddress;
import java.net.MalformedURLException;
import java.net.URL;

public class UrlValidator {

    /**
     * 验证URL的主机是否可解析。
     * @param urlString 用户输入的URL字符串
     * @return 如果主机可解析且URL语法正确，则返回true；否则返回false。
     */
    public static boolean isHostResolvable(String urlString) {
        if (urlString == null || urlString.trim().isEmpty()) {
            return false;
        }

        try {
            // 1. 基本URL语法验证并提取主机名
            URL url = new URL(urlString);
            String host = url.getHost();

            // 如果URL没有指定主机（例如，"file:///path"），则不适用此方法
            if (host == null || host.isEmpty()) {
                System.out.println("URL '" + urlString + "' does not contain a valid host.");
                return false;
            }

            // 2. 尝试解析主机名
            // 通常使用HTTP/HTTPS的默认端口（80或443），这里以80为例
            // 注意：这只是检查DNS解析，不代表端口一定开放或服务可用
            InetSocketAddress socketAddress = new InetSocketAddress(host, 80);

            // 3. 检查解析结果
            if (socketAddress.isUnresolved()) {
                System.out.println("Host '" + host + "' for URL '" + urlString + "' is unresolved (DNS lookup failed).");
                return false;
            } else {
                System.out.println("Host '" + host + "' for URL '" + urlString + "' is resolvable to IP: " + socketAddress.getAddress().getHostAddress());
                return true;
            }
        } catch (MalformedURLException e) {
            System.out.println("URL '" + urlString + "' is malformed: " + e.getMessage());
            return false;
        } catch (SecurityException e) {
            // 某些环境下可能存在安全管理器阻止DNS解析
            System.out.println("SecurityException during host resolution for URL '" + urlString + "': " + e.getMessage());
            return false;
        } catch (Exception e) {
            // 捕获其他潜在异常
            System.out.println("An unexpected error occurred during URL validation for '" + urlString + "': " + e.getMessage());
            return false;
        }
    }

    public static void main(String[] args) {
        // 测试有效URL
        System.out.println("Validation for 'http://www.google.com': " + isHostResolvable("http://www.google.com"));
        System.out.println("Validation for 'https://www.baidu.com': " + isHostResolvable("https://www.baidu.com"));

        // 测试无效主机
        System.out.println("Validation for 'http://www.notARealSite.com': " + isHostResolvable("http://www.notARealSite.com"));
        System.out.println("Validation for 'http://this-host-definitely-does-not-exist-12345.com': " + isHostResolvable("http://this-host-definitely-does-not-exist-12345.com"));

        // 测试语法错误URL
        System.out.println("Validation for 'invalid-url': " + isHostResolvable("invalid-url"));

        // 测试没有主机的URL
        System.out.println("Validation for 'file:///C:/temp/test.txt': " + isHostResolvable("file:///C:/temp/test.txt"));
    }
}