使用WebDriverWait类处理等待（sleep）的问题

用selenium进行web UI的自动化开发时，经常遇到loading需要等待的时候，或者需要验证一个action之后某个dialog是否呈现或者消失。对于这类情况是不建议用sleep(xx)来死等，因为你无法准确判断要等多久，少了就会报error，多了就会浪费整个脚本跑的时间。聪明的做法就是灵活等待，WebDriverWait（org.openqa.selenium.support.ui）这个类是很好的选择。

/**
* Wait until the element visible with customized timeout
* @param driver
* @param locator
* @param errorMessage
* @return
*/
public WebElement waitForElementVisible(WebDriver driver,final By locator, long timeOutInSeconds, String errorMessage) {
Function<WebDriver, WebElement> waitFn = new Function<WebDriver, WebElement>() {
@Override
public WebElement apply(WebDriver driver) {
try {
WebElement el = driver.findElement(locator);
if (el.isDisplayed()) {
return el;
}
} catch (Exception e) {
}
return null;
}
};

WebDriverWait wait = new WebDriverWait(driver, timeOutInSeconds);
if (errorMessage != "") {
wait.withMessage(errorMessage);
} else {
wait.withMessage("Cannot find Element: " + locator.toString());
}
return wait.until(waitFn);
}

/**
* Wait until the element present with customized timeout
* @param driver
* @param locator
* @param errorMessage
* @return
*/
public Boolean waitForElementPresent(WebDriver driver,final By locator, long timeOutInSeconds, String errorMessage) {
Function<WebDriver, Boolean> waitFn = new Function<WebDriver, Boolean>() {
@Override
public Boolean apply(WebDriver driver) {
try {
driver.findElement(locator);
return true;
} catch (Exception e) {
return false;
}
}
};

WebDriverWait wait = new WebDriverWait(driver, timeOutInSeconds);
if (errorMessage != "") {
wait.withMessage(errorMessage);
} else {
wait.withMessage("Cannot find Element: " + locator.toString());
}
return wait.until(waitFn);
}