Selenium WebDriver使用经验杂记

原文地址：http://blog.csdn.net/ant_yan/article/details/8185899

(一) To Handle Ajax

Selenium WebDriver在加载页面的时候，无论是driver.get(url)或者driver.getPageSource()，会立即返回当时页面的数据。但当代的网页技术都大量使用了异步Ajax调用，这使得许多DOM元素的创建和加载，都分布在页面load结束后的许多零散的时间点，让WebDriver的findElement经常无功而返。这个时候，一般有两种方式来解决问题：

1. 利用Selenium WebDriver原生的API，进行预判等待元素出现
演示代码如下：
使用FluentWait + Predicate接口

FluentWait<By> fluentWait = new FluentWait<By>(By.tagName("TEXTAREA"));
fluentWait.pollingEvery(100, TimeUnit.MILLISECONDS);
fluentWait.withTimeout(1000, TimeUnit.MILLISECONDS);
fluentWait.until(new Predicate<By>() {
    public boolean apply(By by) {
        try {
             return browser.findElement(by).isDisplayed();
        } catch (NoSuchElementException ex) {
             return false;
        }
    }
});

browser.findElement(By.tagName("TEXTAREA")).sendKeys("text to enter");

FluentWait<By> fluentWait = new FluentWait<By>(By.tagName("TEXTAREA"));  
fluentWait.pollingEvery(100, TimeUnit.MILLISECONDS);  
fluentWait.withTimeout(1000, TimeUnit.MILLISECONDS);  
fluentWait.until(new Predicate<By>() {  
	public boolean apply(By by) {  
		try {  
			return browser.findElement(by).isDisplayed();  
		} catch (NoSuchElementException ex) {  
			return false;  
		}  
	}  
});  

browser.findElement(By.tagName("TEXTAREA")).sendKeys("text to enter"); 

或者也可以直接使用Wait接口的until方法，传入一个ExpectedCondition

public ExpectedCondition<WebElement> visibilityOfElementLocated(final By by) {
    return new ExpectedCondition<WebElement>() {
           public WebElement apply(WebDriver driver) {
            WebElement element = driver.findElement(by);
             return element.isDisplayed() ? element :null;
          }
    };
}

public  void performSomeAction() {
    ..
    ..
    Wait<WebDriver> wait =  new WebDriverWait(driver,20);
    WebElement element = wait.until(visibilityOfElementLocated(By.tagName("a")));
    ..
}

public ExpectedCondition<WebElement> visibilityOfElementLocated(final By by) {  
	return new ExpectedCondition<WebElement>() {  
		  public WebElement apply(WebDriver driver) {  
			WebElement element = driver.findElement(by);  
			return element.isDisplayed() ? element : null;  
		  }  
	};  
}  
	
public void performSomeAction() {  
	..  
	..  
	Wait<WebDriver> wait = new WebDriverWait(driver, 20);  
	WebElement element = wait.until(visibilityOfElementLocated(By.tagName("a")));  
	..          
}  

2. 利用Javascript注入，来读取不同Ajax调用框架的Ajax request status，一直等到Ajax调用全部返回才开始分析操作Dom元素
演示代码如下：

protected void syncAjaxByJQuery(String timeout) {
    boolean isSucceed = false;
    try {
        selenium.waitForCondition(
                 "selenium.browserbot.getCurrentWindow().jQuery.active == 0", timeout);
        isSucceed =  true;
    } catch (SeleniumException se) {
        LOG.error(se);
    } catch (Exception re) {
        throw new RuntimeException(re.getMessage());
    }
    operationCheck(isSucceed);
}


protected void syncAjaxByPrototype(String timeout) {
    boolean isSucceed = false;
    try {
        selenium.waitForCondition(
                "selenium.browserbot.getCurrentWindow().Ajax.activeRequestCount == 0",
                timeout);
        isSucceed =  true;
    } catch (SeleniumException se) {
        LOG.error(se);
    } catch (Exception re) {
        throw new RuntimeException(re.getMessage());
    }
    operationCheck(isSucceed);
}


protected void syncAjaxByDojo(String timeout) {
    boolean isSucceed = false;
    try {
        selenium.waitForCondition(
                "selenium.browserbot.getCurrentWindow().dojo.io.XMLHTTPTransport.inFlight.length == 0",
                timeout);
        isSucceed =  true;
    } catch (SeleniumException se) {
        LOG.error(se);
    } catch (Exception re) {
        throw new RuntimeException(re.getMessage());
    }
    operationCheck(isSucceed);
}

protected void syncAjaxByJQuery(String timeout) {  
	boolean isSucceed = false;  
	try {  
		selenium.waitForCondition(  
				"selenium.browserbot.getCurrentWindow().jQuery.active == 0", timeout);  
		isSucceed = true;  
	} catch (SeleniumException se) {  
		LOG.error(se);  
	} catch (Exception re) {  
		throw new RuntimeException(re.getMessage());  
	}  
	operationCheck(isSucceed);  
}


protected void syncAjaxByPrototype(String timeout) {  
	boolean isSucceed = false;  
	try {  
		selenium.waitForCondition(  
				"selenium.browserbot.getCurrentWindow().Ajax.activeRequestCount == 0",  
				timeout);  
		isSucceed = true;  
	} catch (SeleniumException se) {  
		LOG.error(se);  
	} catch (Exception re) {  
		throw new RuntimeException(re.getMessage());  
	}  
	operationCheck(isSucceed);  
}


protected void syncAjaxByDojo(String timeout) {  
	boolean isSucceed = false;  
	try {  
		selenium.waitForCondition(  
				"selenium.browserbot.getCurrentWindow().dojo.io.XMLHTTPTransport.inFlight.length == 0",  
				timeout);  
		isSucceed = true;  
	} catch (SeleniumException se) {  
		LOG.error(se);  
	} catch (Exception re) {  
		throw new RuntimeException(re.getMessage());  
	}  
	operationCheck(isSucceed);  
}

(二) To Handle Alert

最近遇到许多网页用Selenium操作的时候，网页本身会弹出许多Alert模态窗口，这种模态窗口会阻断driver继续执行。虽然WebDriver已经提供了些许方法来处理模态Alert窗口，但是依然会在不同的浏览器上存在未修复的Bug。先来看看WebDriver提供的处理Alert的方式，基本就是通过driver.switchTo()方法获得Alert模态窗口的句柄，然后调用Alert.accept()或者Alert.dismiss()方法接受或者拒绝，同样的操作也适用于Confirm窗口。我为了防止意外情况下WebDriver内置Alert处理的代码会崩溃，所以特意设计了一个超时机制，一旦超时就转而使用原始键盘模拟输入回车来消除窗口，使用的也是java.awt.Robot类来模拟操作系统的键盘输入动作。

演示代码如下：     

public T handleAlert(){
    KeyboardUtils.enter();
    long clockTime = System.currentTimeMillis();
    long timeout = 3 *1000;
    while(true){
        if((System.currentTimeMillis()-clockTime) > timeout){
            KeyboardUtils.enter();
            break;
        }else if(WebDriverUtils.isAlertExist(driver)){
            try{
                Alert alert = driver.switchTo().alert();
                alert.getText();
                alert.accept();
            }catch(Exception ex){
                KeyboardUtils.enter();
            }
        }

        waiting(300);
    }
    return instance;
}


//In WebDriverUtils.class
public  staticboolean isAlertExist(WebDriver driver){
    try{
        driver.switchTo().alert();
         return true;
    }catch(NoAlertPresentException  ex){
         return false;
    }
}

public T handleAlert(){
	KeyboardUtils.enter();
	long clockTime = System.currentTimeMillis();
	long timeout = 3 * 1000;
	while(true){
		if((System.currentTimeMillis()-clockTime) > timeout){
			KeyboardUtils.enter();
			break;
		}else if(WebDriverUtils.isAlertExist(driver)){
			try{
				Alert alert = driver.switchTo().alert();
				alert.getText();
				alert.accept();
			}catch(Exception ex){
				KeyboardUtils.enter();
			}
		}
		
		waiting(300);
	}	
	return instance;
}


//In WebDriverUtils.class
public static boolean isAlertExist(WebDriver driver){
	try{
		driver.switchTo().alert();
		return true;
	}catch(NoAlertPresentException  ex){
		return false;
	}
}

(三) To Handle more than Alert
还有一种情况，当我用Firefox打开某些游戏网页的时候，网页本身可能是Flash展示，它会自动触发Firefox弹出收藏窗口，添加本页进浏览器的Bookmark，这种窗口一旦出现，driver直接停止响应，代码本身都不会再继续往下走了。所以更别提你下面还有处理Alert窗口的代码，那都是浮云，本线程直接就阻塞了，这一度让我非常的火大。后来实在没办法，想了一种折中的方式，设计了另外一个线程进行心跳检测。主线程如果一直都持续运行，定期汇报心跳。一旦超过一段时间没有收到心跳信号，那么独立的心跳检测线程就会试图去模拟回车输入，或者其他动作，来进一步确保浏览器不会被各种奇怪的现象阻塞不能继续。


(四) Other Tips
1. 加载IEDriver的时候，通常会因为兼容模式的设置问题，而无法启动，尝试在创建IEDriver对象的时候，加入合适的参数设置：

DesiredCapabilities ieCapabilities = DesiredCapabilities.internetExplorer();
ieCapabilities.setCapability(InternetExplorerDriver.INTRODUCE_FLAKINESS_BY_IGNORING_SECURITY_DOMAINS,true);
return new InternetExplorerDriver(ieCapabilities);

DesiredCapabilities ieCapabilities = DesiredCapabilities.internetExplorer(); 
ieCapabilities.setCapability(InternetExplorerDriver.INTRODUCE_FLAKINESS_BY_IGNORING_SECURITY_DOMAINS, true);
return new InternetExplorerDriver(ieCapabilities);

2. 关闭浏览器的时候，例如新浪主页，本身会弹出一个独立的广告窗口，如果调用driver.close的时候句柄焦点在主窗口上，那么广告窗口是无法关闭的。所以在关闭driver之前，试图检查一下还有无别的独立窗口句柄存在：

public staticvoid closeWebDriver(WebDriver driver){
    if(driver == null)
         return;

    try{
        String current = driver.getWindowHandle();
        Set<String> otherWins = driver.getWindowHandles();
        for(String winId : otherWins)
             if(winId.equals(current))
                continue;
             else
                driver.switchTo().window(winId).close();
    }catch(Exception ex){
        //ignore
    }finally{
        try{
            driver.quit();
        }catch(Exception ex){}
    }
}

public static void closeWebDriver(WebDriver driver){
	if(driver == null)
		return;
	
	try{
		String current = driver.getWindowHandle();
		Set<String> otherWins = driver.getWindowHandles();
		for(String winId : otherWins)
			if(winId.equals(current))
				continue;
			else
				driver.switchTo().window(winId).close();
	}catch(Exception ex){
		//ignore
	}finally{
		try{
			driver.quit();
		}catch(Exception ex){}
	}
}

3. 如何使用WebDriver进行网页截图，提示一点在Flash页面中截图可能会得到一片黑色的屏幕，另外WebDriver截图会把当时整个网页哪怕是需要滚动才显示出来的部分，都会包含在截图里面。

public static String takeScreenshot(WebDriver driver, String savePath,long delay){
     try {
        CommonUtils.waiting(delay * 1000);
        File screenShotFile = ((TakesScreenshot)driver).getScreenshotAs(OutputType.FILE);
        String path =  "screenshot/"+savePath;
        if(!savePath.endsWith("/.png"))
            path = path +  ".png";

        FileUtils.copyFile(screenShotFile, new File(path));
        LOG.info("Take screenshot at "+savePath);
         return path;
    } catch (IOException ex) {
        LOG.warn("failed to take screenshot for current page, caused by "+ex.getMessage());
        return null;
    }
}