java - 我如何扩展 Selenium By.class 以创造更大的灵活性？

Question

我如何扩展 Selenium By.class 以创造更大的灵 active ？我看着 By.class我不太清楚如何处理这个问题。看来我需要创建一个接口(interface)类和一个静态 By 类，例如 ByJavascriptGetWebElement，才能创建这种包装器？

我希望能够这样调用它:

By.javascript("return document.querySelector(\"div#item div\");", el );

我也听说过一种更简单的方法，但我更愿意用更传统的方法:

public By byJavascriptGetElement( WebElement we ) {
    return By.  ???
}

有什么想法吗？

Answer 1

这其实很容易做到。

这个想法是访问 WebDriver 实例并在其上运行 JavaScript(如果它支持的话)。然后是大量的验证，因为我们需要确保只返回我们 promise 的内容。

ByJavaScript 类本身如下所示:

public class ByJavaScript extends By implements Serializable {
    private final String script;

    public ByJavaScript(String script) {
        checkNotNull(script, "Cannot find elements with a null JavaScript expression.");
        this.script = script;
    }

    @Override
    public List<WebElement> findElements(SearchContext context) {
        JavascriptExecutor js = getJavascriptExecutorFromSearchContext(context);

        // call the JS, inspect and validate response
        Object response = js.executeScript(script);
        List<WebElement> elements = getElementListFromJsResponse(response);

        // filter out the elements that aren't descendants of the context node
        if (context instanceof WebElement) {
            filterOutElementsWithoutCommonAncestor(elements, (WebElement)context);
        }

        return elements;
    }

    private static JavascriptExecutor getJavascriptExecutorFromSearchContext(SearchContext context) {
        if (context instanceof JavascriptExecutor) {
            // context is most likely the whole WebDriver
            return (JavascriptExecutor)context;
        }
        if (context instanceof WrapsDriver) {
            // context is most likely some WebElement
            WebDriver driver = ((WrapsDriver)context).getWrappedDriver();
            checkState(driver instanceof JavascriptExecutor, "This WebDriver doesn't support JavaScript.");
            return (JavascriptExecutor)driver;
        }
        throw new IllegalStateException("We can't invoke JavaScript from this context.");
    }

    @SuppressWarnings("unchecked")  // cast thoroughly checked
    private static List<WebElement> getElementListFromJsResponse(Object response) {
        if (response == null) {
            // no element found
            return Lists.newArrayList();
        }
        if (response instanceof WebElement) {
            // a single element found
            return Lists.newArrayList((WebElement)response);
        }
        if (response instanceof List) {
            // found multiple things, check whether every one of them is a WebElement
            checkArgument(
                    Iterables.all((List<?>)response, Predicates.instanceOf(WebElement.class)),
                    "The JavaScript query returned something that isn't a WebElement.");
            return (List<WebElement>)response;  // cast is checked as far as we can tell
        }
        throw new IllegalArgumentException("The JavaScript query returned something that isn't a WebElement.");
    }

    private static void filterOutElementsWithoutCommonAncestor(List<WebElement> elements, WebElement ancestor) {
        for (Iterator<WebElement> iter = elements.iterator(); iter.hasNext(); ) {
            WebElement elem = iter.next();

            // iterate over ancestors
            while (!elem.equals(ancestor) && !elem.getTagName().equals("html")) {
                elem = elem.findElement(By.xpath("./.."));
            }

            if (!elem.equals(ancestor)) {
                iter.remove();
            }
        }
    }

    @Override
    public String toString() {
          return "By.javaScript: \"" + script + "\"";
    }

}

^{此代码使用 the Google Guava library .它是 Selenium 的依赖项，因此您应该将它放在类路径中。但如果有什么不明白的地方，请查看 Guava。}

需要考虑的事项:

1. 记录整个事情。
2. 使用更好、更有帮助的异常。考虑 WebDriverException 的一些自定义子类。还可以添加更多有用的消息和信息。
3. 限制类对包的可见性。或者将其嵌入静态工厂(如原始 By 类中所示)，这样就无法直接访问它等。
4. 编写测试。我已经尝试了最明显的用法(无法找到元素、从驱动程序中搜索、从某些上下文中搜索)并且一切似乎都正常，但我没有对其进行广泛测试。

用法:

WebElement elem = driver.findElement(new ByJavaScript("return document.querySelector('.haha');"));

现在，原来的 By 类是一个静态工厂，它给出了自己的各种实现。不幸的是，我们无法向它添加新的静态方法(不更改其源代码)，因此我们将无法键入 By.javascript("return something;")。我们必须创建自己的静态工厂来获得类似的东西:

public class MyBy {
    /**
     * Returns a {@code By} which locates elements by the JavaScript expression passed to it.
     * 
     * @param script The JavaScript expression to run and whose result to return
     */
    public static By javascript(String script) {
        return new ByJavaScript(script);
    }
}

用法:

WebElement elem = driver.findElement(MyBy.javascript("return document.querySelector('.haha');"));