java - Selenium 火 StaleElementReferenceException

Question

我尝试用selenium 制作一个网络爬虫。我的程序引发 StaleElementReferenceException。我认为这是因为我递归地抓取页面，并且当页面没有更多链接时，该函数导航到下一页，而不是之前导航到父页面。

因此，我引入了一个树形数据结构，当当前 url 不等于父 url 时导航回父级。但这不是我的问题的解决方案。

有人可以帮我吗？

代码:

public class crawler {
    private static FirefoxDriver driver;
    private static String main_url = "https://robhammond.co/tools/seo-crawler";
    private static List<String> uniqueLinks = new ArrayList<String>();

    public static void main(String[] args) {
        driver = new FirefoxDriver();

        Node<String> root = new Node<>(main_url);

        scrape(root, main_url);
    }

    public static void scrape(Node<String> node, String url) {
        if(node.getParent() != null && (!driver.getCurrentUrl().equals(node.getParent().getData()))) {
            driver.navigate().to(node.getParent().getData());
        }

        driver.navigate().to(url);

        List<WebElement> allLinks = driver.findElements(By.tagName("a"));

        for(WebElement link : allLinks) {
            if(link.getAttribute("href").contains(main_url) && !uniqueLinks.contains(link.getAttribute("href")) && link.isDisplayed()) {
                uniqueLinks.add(link.getAttribute("href"));

                System.out.println(link.getAttribute("href"));

                scrape(new Node<>(link.getAttribute("href")), link.getAttribute("href"));
            }
        }
    }
}

这是控制台的输出:

D:\Programme\openjdk-12.0.1_windows-x64_bin\jdk-12.0.1\bin\java.exe "-javaagent:D:\Programme\JetBrains\IntelliJ IDEA 2019.1.2\lib\idea_rt.jar=60461:D:\Programme\JetBrains\IntelliJ IDEA 2019.1.2\bin" -Dfile.encoding=UTF-8 -classpath C:\Users\admin\Desktop\SeleniumWebScraper\out\production\SeleniumWebScraper;D:\Downloads\selenium-server-standalone-3.141.59.jar de.company.crawler.crawler
1557924446770   mozrunner::runner   INFO    Running command: "C:\\Program Files\\Mozilla Firefox\\firefox.exe" "-marionette" "-foreground" "-no-remote" "-profile" "C:\\Users\\admin\\AppData\\Local\\Temp\\rust_mozprofile.YqmEqE8y1pjv"
1557924447037   addons.webextension.screenshots@mozilla.org WARN    Loading extension 'screenshots@mozilla.org': Reading manifest: Invalid extension permission: mozillaAddons
1557924447037   addons.webextension.screenshots@mozilla.org WARN    Loading extension 'screenshots@mozilla.org': Reading manifest: Invalid extension permission: resource://pdf.js/
1557924447037   addons.webextension.screenshots@mozilla.org WARN    Loading extension 'screenshots@mozilla.org': Reading manifest: Invalid extension permission: about:reader*
1557924448047   Marionette  INFO    Listening on port 60468
1557924448383   Marionette  WARN    TLS certificate errors will be ignored for this session
Mai 15, 2019 2:47:28 NACHM. org.openqa.selenium.remote.ProtocolHandshake createSession
INFO: Detected dialect: W3C
JavaScript warning: https://robhammond.co/js/jquery.min.js, line 4: Using //@ to indicate sourceMappingURL pragmas is deprecated. Use //# instead
https://robhammond.co/tools/seo-crawler#content
https://twitter.com/intent/tweet?text=SEO%20Crawler&url=https://robhammond.co/tools/seo-crawler&via=robhammond
Exception in thread "main" org.openqa.selenium.StaleElementReferenceException: The element reference of <a href="/tools/"> is stale; either the element is no longer attached to the DOM, it is not in the current frame context, or the document has been refreshed
For documentation on this error, please visit: https://www.seleniumhq.org/exceptions/stale_element_reference.html
Build info: version: '3.141.59', revision: 'e82be7d358', time: '2018-11-14T08:25:53'
System info: host: 'DESKTOP-admin', ip: '192.168.233.1', os.name: 'Windows 10', os.arch: 'amd64', os.version: '10.0', java.version: '12.0.1'
Driver info: org.openqa.selenium.firefox.FirefoxDriver
Capabilities {acceptInsecureCerts: true, browserName: firefox, browserVersion: 66.0.5, javascriptEnabled: true, moz:accessibilityChecks: false, moz:geckodriverVersion: 0.24.0, moz:headless: false, moz:processID: 19124, moz:profile: C:\Users\admin\AppData\Loca..., moz:shutdownTimeout: 60000, moz:useNonSpecCompliantPointerOrigin: false, moz:webdriverClick: true, pageLoadStrategy: normal, platform: WINDOWS, platformName: WINDOWS, platformVersion: 10.0, rotatable: false, setWindowRect: true, strictFileInteractability: false, timeouts: {implicit: 0, pageLoad: 300000, script: 30000}, unhandledPromptBehavior: dismiss and notify}
Session ID: b3b87675-57c8-4b48-9a20-8df5e4d37503
    at java.base/jdk.internal.reflect.NativeConstructorAccessorImpl.newInstance0(Native Method)
    at java.base/jdk.internal.reflect.NativeConstructorAccessorImpl.newInstance(NativeConstructorAccessorImpl.java:62)
    at java.base/jdk.internal.reflect.DelegatingConstructorAccessorImpl.newInstance(DelegatingConstructorAccessorImpl.java:45)
    at java.base/java.lang.reflect.Constructor.newInstanceWithCaller(Constructor.java:500)
    at java.base/java.lang.reflect.Constructor.newInstance(Constructor.java:481)
    at org.openqa.selenium.remote.http.W3CHttpResponseCodec.createException(W3CHttpResponseCodec.java:187)
    at org.openqa.selenium.remote.http.W3CHttpResponseCodec.decode(W3CHttpResponseCodec.java:122)
    at org.openqa.selenium.remote.http.W3CHttpResponseCodec.decode(W3CHttpResponseCodec.java:49)
    at org.openqa.selenium.remote.HttpCommandExecutor.execute(HttpCommandExecutor.java:158)
    at org.openqa.selenium.remote.service.DriverCommandExecutor.execute(DriverCommandExecutor.java:83)
    at org.openqa.selenium.remote.RemoteWebDriver.execute(RemoteWebDriver.java:552)
    at org.openqa.selenium.remote.RemoteWebElement.execute(RemoteWebElement.java:285)
    at org.openqa.selenium.remote.RemoteWebElement.getAttribute(RemoteWebElement.java:134)
    at de.company.crawler.crawler.scrape(crawler.java:33)
    at de.company.crawler.crawler.scrape(crawler.java:38)
    at de.company.crawler.crawler.main(crawler.java:20)

Process finished with exit code 1

Answer 1

1. 当您离开首页时，所有WebElements在 allLinks 列表中丢失。

   我建议将其从 WebElement 列表转换为普通 Strings 列表像:

   List<String> allLinksHrefs = allLinks.stream().map(link -> link.getAttribute("href")).collect(Collectors.toList());
   

   并迭代这个新的 allLinksHrefs 列表。

2. 您可以使用基于哈希的集合来保存uniqueLinks，例如 HashSet - 这样重复项将被自动消除
3. 当前方法可能需要几天时间才能完成，请考虑使用 Selenium Grid和 running your scraper in Parallel