[selenium-webdriver] What is the use of DesiredCapabilities in Selenium WebDriver?

What is the use of DesiredCapabilities in Selenium WebDriver?

When we want to use this and how?

Answer with example would be appreciated.

Desired capabilities comes in handy while doing remote or parallel execution using selenium grid. We will be parametrizing the browser details and passing in to selenium server using desired capabilities class.

Another usage is, test automation using Appium as shown below

// Created object of DesiredCapabilities class. 
DesiredCapabilities capabilities = new DesiredCapabilities(); 
// Set android deviceName desired capability. Set your device name. 
capabilities.setCapability("deviceName", "your Device Name"); 
// Set BROWSER_NAME desired capability. 
capabilities.setCapability(CapabilityType.BROWSER_NAME, "Chrome"); 
// Set android VERSION desired capability. Set your mobile device's OS version. 
capabilities.setCapability(CapabilityType.VERSION, "5.1"); 
// Set android platformName desired capability. It's Android in our case here. 
capabilities.setCapability("platformName", "Android"); 

I know I am very late to answer this question.
But would like to add for further references to the give answers.
DesiredCapabilities are used like setting your config with key-value pair.
Below is an example related to Appium used for Automating Mobile platforms like Android and IOS.
So we generally set DesiredCapabilities for conveying our WebDriver for specific things we will be needing to run our test to narrow down the performance and to increase the accuracy.

So we set our DesiredCapabilities as:

// Created object of DesiredCapabilities class.
DesiredCapabilities capabilities = new DesiredCapabilities();

// Set android deviceName desired capability. Set your device name.
capabilities.setCapability("deviceName", "your Device Name");

// Set BROWSER_NAME desired capability.
capabilities.setCapability(CapabilityType.BROWSER_NAME, "Chrome");

// Set android VERSION desired capability. Set your mobile device's OS version.
capabilities.setCapability(CapabilityType.VERSION, "5.1");

// Set android platformName desired capability. It's Android in our case here.
capabilities.setCapability("platformName", "Android");

// Set android appPackage desired capability.

//You need to check for your appPackage Name for your app, you can use this app for that APK INFO

// Set your application's appPackage if you are using any other app. 
capabilities.setCapability("appPackage", "com.android.appPackageName");

// Set android appActivity desired capability. You can use the same app for finding appActivity of your app
capabilities.setCapability("appActivity", "com.android.calculator2.Calculator");

This DesiredCapabilities are very specific to Appium on Android Platform. For more you can refer to the official site of Selenium desiredCapabilities class

When you run selenium WebDriver, the WebDriver opens a remote server in your computer's local host. Now, this server, called the Selenium Server, is used to interpret your code into actions to run or "drive" the instance of a real browser known as either chromebrowser, ie broser, ff browser, etc.

So, the Selenium Server can interact with different browser properties and hence it has many "capabilities".

Now what capabilities do you desire? Consider a scenario where you are validating if files have been downloaded properly in your app but, however, you do not have a desktop automation tool. In the case where you click the download link and a desktop pop up shows up to ask where to save and/or if you want to download. Your next route to bypass that would be to suppress that pop up. How? Desired Capabilities.

There are other such examples. In summary, Selenium Server can do a lot, use Desired Capabilities to tailor it to your need.

1. It is a class in org.openqa.selenium.remote.DesiredCapabilities package.
2. It gives facility to set the properties of browser. Such as to set BrowserName, Platform, Version of Browser.
3. Mostly DesiredCapabilities class used when do we used Selenium Grid.
4. We have to execute mutiple TestCases on multiple Systems with different browser with Different version and Different Operating System.

Example:

WebDriver driver;
String baseUrl , nodeUrl;
baseUrl = "https://www.facebook.com";
nodeUrl = "http://192.168.10.21:5568/wd/hub";

DesiredCapabilities capability = DesiredCapabilities.firefox();
capability.setBrowserName("firefox");
capability.setPlatform(Platform.WIN8_1);

driver = new RemoteWebDriver(new URL(nodeUrl),capability);
driver.manage().window().maximize();
driver.manage().timeouts().implicitlyWait(2, TimeUnit.MINUTES);

DesiredCapabilities are options that you can use to customize and configure a browser session.

You can read more about them here!