44Selenium WebDriver

44.1 WebDriver architecture

Selenium WebDriver is a client–server protocol. Your test (client binding) sends commands as HTTP requests to a browser driver (chromedriver, geckodriver), which translates them into native browser automation and returns JSON.

Test code  →  [HTTP + JSON]  →  Browser driver  →  [native API]  →  Browser
(Java / Python / C# / JS)     (chromedriver, geckodriver)         (Chrome / Firefox)

Each command = one HTTP round trip. Historically used Selenium's own JSON Wire Protocol; now superseded by the W3C WebDriver standard. Same shape (HTTP+JSON) but standardised endpoints and capability negotiation across browsers.

44.2 What changed in Selenium 4

44.3 Setting up

// Maven dependency
<dependency>
  <groupId>org.seleniumhq.selenium</groupId>
  <artifactId>selenium-java</artifactId>
  <version>4.27.0</version>
</dependency>

// Driver — Selenium Manager (built-in, no manual chromedriver download)
WebDriver driver = new ChromeDriver();
driver.get("https://example.com");
driver.quit();

44.4 Locators

// Standard
driver.findElement(By.id("user"));
driver.findElement(By.name("email"));
driver.findElement(By.className("btn-primary"));
driver.findElement(By.tagName("button"));
driver.findElement(By.linkText("Sign in"));
driver.findElement(By.partialLinkText("Sign"));
driver.findElement(By.cssSelector("input[type=email]"));
driver.findElement(By.xpath("//button[normalize-space()='Submit']"));

// Selenium 4 relative locators
import static org.openqa.selenium.support.locators.RelativeLocator.with;
By passwordField = By.id("password");
WebElement label = driver.findElement(with(By.tagName("label")).above(passwordField));
WebElement nearby = driver.findElement(with(By.tagName("button")).near(passwordField, 100));

44.5 Waits — the most-asked Selenium topic

driver.manage().timeouts().implicitlyWait(Duration.ofSeconds(10));
driver.findElement(By.id("x"));  // polls up to 10 s if not found

WebDriverWait wait = new WebDriverWait(driver, Duration.ofSeconds(10));
WebElement el = wait.until(ExpectedConditions.elementToBeClickable(By.id("x")));

// Fluent wait — custom polling + ignored exceptions
Wait<WebDriver> fluent = new FluentWait<>(driver)
  .withTimeout(Duration.ofSeconds(30))
  .pollingEvery(Duration.ofMillis(500))
  .ignoring(NoSuchElementException.class);
WebElement el = fluent.until(d -> d.findElement(By.id("x")));

44.6 Common interactions

// Click, type
driver.findElement(By.id("user")).sendKeys("alice");
driver.findElement(By.cssSelector("button.primary")).click();

// Dropdown
Select select = new Select(driver.findElement(By.id("country")));
select.selectByVisibleText("India");
select.selectByValue("IN");
select.selectByIndex(2);

// Alerts
Alert alert = driver.switchTo().alert();
String msg = alert.getText();
alert.accept();   // alert.dismiss(); alert.sendKeys("...");

// Frames
driver.switchTo().frame("frame-name");
// ... do stuff ...
driver.switchTo().defaultContent();

// Windows / tabs
String original = driver.getWindowHandle();
driver.switchTo().newWindow(WindowType.TAB);
driver.get("https://other.com");
driver.switchTo().window(original);
for (String h : driver.getWindowHandles()) { /* iterate */ }

// Actions class — chained gestures
new Actions(driver)
  .moveToElement(menu).pause(Duration.ofMillis(200))
  .click(menuItem).keyDown(Keys.SHIFT).click(other).keyUp(Keys.SHIFT).perform();

// JavaScript executor
JavascriptExecutor js = (JavascriptExecutor) driver;
js.executeScript("arguments[0].scrollIntoView(true);", el);
String title = (String) js.executeScript("return document.title;");

44.7 Page Object Model (Selenium-style)

public class LoginPage {
  private final WebDriver driver;
  private final By emailField = By.id("email");
  private final By passwordField = By.id("password");
  private final By submitBtn = By.cssSelector("button[type=submit]");

  public LoginPage(WebDriver driver) { this.driver = driver; }

  public DashboardPage signIn(String email, String pw) {
    driver.findElement(emailField).sendKeys(email);
    driver.findElement(passwordField).sendKeys(pw);
    driver.findElement(submitBtn).click();
    return new DashboardPage(driver);
  }
}

// PageFactory variant
public class LoginPageFactory {
  @FindBy(id = "email") private WebElement email;
  @FindBy(id = "password") private WebElement password;
  @CacheLookup @FindBy(css = "button[type=submit]") private WebElement submit;

  public LoginPageFactory(WebDriver driver) {
    PageFactory.initElements(driver, this);
  }
}

44.8 Selenium Grid 4

Distributed Selenium execution. Hub-node or standalone modes.

# Start a hub
java -jar selenium-server.jar hub

# Register a node
java -jar selenium-server.jar node --hub http://hub:4444

# Or single command for dev
java -jar selenium-server.jar standalone

// Connect to remote
WebDriver driver = new RemoteWebDriver(
    new URL("http://grid:4444"),
    new ChromeOptions());

Selenium Grid 4 added containerised Docker support, observability via OpenTelemetry, and a Studio UI.

44.9 Staleness — the Selenium-only pain

WebElement is a handle to a found node. When the DOM re-renders, the handle becomes stale → StaleElementReferenceException. Mitigations:

• Don't cache WebElements long; re-find before each interaction
• Catch + retry pattern in helpers
• Use explicit waits that re-find each poll
• Avoid @CacheLookup

44.10 Selenium vs Playwright — interview summary