为何执行Selenium链接校验代码时出现ClassCastException异常？

在执行网页链接校验代码时遇到了java.lang.ClassCastException异常，请问是什么原因导致的？

异常信息 #

Exception in thread "main" java.lang.ClassCastException: class sun.net.www.protocol.mailto.MailToURLConnection cannot be cast to class java.net.HttpURLConnection (sun.net.www.protocol.mailto.MailToURLConnection and java.net.HttpURLConnection are in module java.base of loader 'bootstrap')

测试代码 #

package brokenLinks;

import java.io.IOException;
import java.net.HttpURLConnection;
//import java.net.MalformedURLException;
import java.net.URL;
import java.time.Duration;
import java.util.List;

import org.openqa.selenium.By;
import org.openqa.selenium.WebDriver;
import org.openqa.selenium.WebElement;
import org.openqa.selenium.chrome.ChromeDriver;

import io.github.bonigarcia.wdm.WebDriverManager;

public class ValidateBrokenLinksTest {

    public static void main(String[] args) throws IOException {
        //设置WebDriver驱动
        WebDriverManager.chromedriver().setup();
        
        //启动Chrome浏览器驱动
        WebDriver driver = new ChromeDriver();
        
        //最大化浏览器窗口
        driver.manage().window().maximize();
        
        //加载目标网页
        driver.get("https://testerscafe.in/");
        
        //设置隐式等待，等待页面加载
        driver.manage().timeouts().implicitlyWait(Duration.ofSeconds(30));
        
        //获取页面中所有<a>标签元素，存入列表集合
        List<WebElement> elements = driver.findElements(By.tagName("a"));
        
        //获取链接总数
        int size = elements.size();
        System.out.println("网页中的链接总数："+size);
        
        //遍历每个链接，获取其href属性值
        for(WebElement links : elements) {
            String link = links.getAttribute("href");
            
            //将链接加载至URL类实例
            URL url = new URL(link);
          
            
            //建立连接
            HttpURLConnection connection = (HttpURLConnection)(url.openConnection());
            connection.connect();
            
            //校验链接有效性
            if(connection.getResponseCode()>=400) {
                System.out.println(link+" ==> 是失效链接");
            }
            else {
                System.out.println(link+" ==> 是有效链接");
            }
        }
        //关闭浏览器驱动
        driver.quit();
    }
}

原因分析 #

页面中的<a>标签不止包含HTTP/HTTPS协议的网页链接，还可能存在mailto:（邮件链接）、tel:（电话链接）这类非HTTP协议的链接。当你对mailto:类型的链接调用url.openConnection()时，返回的是MailToURLConnection对象，这个类和HttpURLConnection没有继承关系，强行做类型转换就会触发ClassCastException。

解决方案 #

1. 过滤非HTTP/HTTPS链接：只处理以http://或https://开头的链接，跳过其他协议的链接
2. 增加空值校验：避免href属性为空的情况，防止创建URL对象时出错

修改后的代码示例 #

package brokenLinks;

import java.io.IOException;
import java.net.HttpURLConnection;
import java.net.URL;
import java.time.Duration;
import java.util.List;

import org.openqa.selenium.By;
import org.openqa.selenium.WebDriver;
import org.openqa.selenium.WebElement;
import org.openqa.selenium.chrome.ChromeDriver;

import io.github.bonigarcia.wdm.WebDriverManager;

public class ValidateBrokenLinksTest {

    public static void main(String[] args) throws IOException {
        WebDriverManager.chromedriver().setup();
        WebDriver driver = new ChromeDriver();
        driver.manage().window().maximize();
        driver.get("https://testerscafe.in/");
        driver.manage().timeouts().implicitlyWait(Duration.ofSeconds(30));
        
        List<WebElement> elements = driver.findElements(By.tagName("a"));
        int size = elements.size();
        System.out.println("网页中的链接总数："+size);
        
        for(WebElement links : elements) {
            String link = links.getAttribute("href");
            
            // 跳过空链接和非HTTP/HTTPS协议的链接
            if(link == null || !link.startsWith("http")) {
                System.out.println(link+" ==> 非HTTP/HTTPS链接，跳过校验");
                continue;
            }
            
            URL url = new URL(link);
            HttpURLConnection connection = (HttpURLConnection)(url.openConnection());
            connection.connect();
            
            if(connection.getResponseCode()>=400) {
                System.out.println(link+" ==> 是失效链接");
            } else {
                System.out.println(link+" ==> 是有效链接");
            }
            // 关闭连接释放资源
            connection.disconnect();
        }
        driver.quit();
    }
}

内容的提问来源于stack exchange，提问作者M S