CLI options in the Selenium Grid

ChromeOptions options = new ChromeOptions();
options.setCapability("gsg:customcap", true);
WebDriver driver = new RemoteWebDriver(new URL("http://localhost:4444"), options);
driver.get("https://selenium.dev");
driver.quit();

curl -X GET "http://localhost:4444/session/<sessionId>/se/file?filename=my_file.pdf"

import static org.openqa.selenium.remote.http.Contents.string;

import java.io.File;
import java.io.IOException;
import java.net.URL;
import java.util.Map;
import java.util.concurrent.TimeUnit;
import org.openqa.selenium.By;
import org.openqa.selenium.WebElement;
import org.openqa.selenium.firefox.FirefoxOptions;
import org.openqa.selenium.io.Zip;
import org.openqa.selenium.json.Json;
import org.openqa.selenium.remote.RemoteWebDriver;
import org.openqa.selenium.remote.http.HttpClient;
import org.openqa.selenium.remote.http.HttpMethod;
import org.openqa.selenium.remote.http.HttpRequest;
import org.openqa.selenium.remote.http.HttpResponse;

public class DownloadsSample {

  public static void main(String[] args) throws InterruptedException, IOException {
    // Make sure the following directory exists on your machine
    File dirToCopyTo = new File("/usr/downloads/file");
    // Assuming the Grid is running locally.
    URL gridUrl = new URL("http://localhost:4444");
    RemoteWebDriver driver = new RemoteWebDriver(gridUrl, firefoxOptions());
    // This public website resets the available files for dowload on a daily basis, 
    // check the name of the file that will be downloaded and replace it below.
    driver.get("http://the-internet.herokuapp.com/download");
    WebElement element = driver.findElement(By.cssSelector(".example a"));
    element.click();

    // The download happens in a remote Node, which makes difficult to know when the file 
    // has been completely downloaded. For demonstration purposes, this example uses a 
    // 10 second sleep which should be enough time for a file to be downloaded. 
    // We strongly recommend to avoid hardcoded sleeps, and ideally, to modify your 
    // application under test so it offers a way to know when the file has been completely 
    // downloaded. 
    TimeUnit.SECONDS.sleep(10);

    HttpRequest request = new HttpRequest(HttpMethod.GET, String.format("/session/%s/se/file", driver.getSessionId()));
    request.addQueryParameter("filename", "my_file.pdf");
    try (HttpClient client = HttpClient.Factory.createDefault().createClient(gridUrl)) {
      HttpResponse response = client.execute(request);
      Map<String, Object> map = new Json().toType(string(response), Json.MAP_TYPE);
      // The returned map would contain 2 keys,
      // filename - This represents the name of the file (same as what was provided by the test)
      // contents - Base64 encoded String which contains the zipped file.
      String encodedContents = map.get("contents").toString();

      //The file contents would always be a zip file and has to be unzipped.
      Zip.unzip(encodedContents, dirToCopyTo);
    } finally {
      driver.quit();
    }
  }

  private static FirefoxOptions firefoxOptions() {
    FirefoxOptions options = new FirefoxOptions();
    // Options specific for Firefox to avoid prompting a dialog for downloads. They might 
    // change in the future, so please refer to the Firefox documentation for up to date details.
    options.addPreference("browser.download.manager.showWhenStarting", false);
    options.addPreference("browser.helperApps.neverAsk.saveToDisk",
        "images/jpeg, application/pdf, application/octet-stream");
    options.addPreference("pdfjs.disabled", true);
    return options;
  }
}