selenium fire StaleElementReferenceException

Question

i try to make a web crawler with selenium. My program fire a StaleElementReferenceException. I thought that were because i crawl a page recursive and when a page have no more links the function navigate to next page and not previously to the parent page.

Therefore i have introduced a tree data structure to navigate back to the parent when the current url not equal the parent url. But this was not the solution for my problem.

Can anybody help me?

Code:

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);

        scrap(root, main_url);
    }

    public static void scrap(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"));

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

And this is the output from the console:

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   [e-mail] WARN    Loading extension '[e-mail]': Reading manifest: Invalid extension permission: mozillaAddons
1557924447037   [e-mail] WARN    Loading extension '[e-mail]': Reading manifest: Invalid extension permission: resource://pdf.js/
1557924447037   [e-mail] WARN    Loading extension '[e-mail]': 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.scrap(crawler.java:33)
    at de.company.crawler.crawler.scrap(crawler.java:38)
    at de.company.crawler.crawler.main(crawler.java:20)

Process finished with exit code 1

Answer 1

1. When you navigate away from the first page all WebElements in the allLinks list get lost.

   I would recommend converting it from the list of WebElement to the list of normal Strings like:

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

   and iterate through this new allLinksHrefs list instead.

2. You can use a hash-based collection for holding the uniqueLinks like HashSet - this way duplicates will be automatically eliminated
3. The current approach can take days to complete, consider using Selenium Grid and running your scraper in Parallel