How to set default download directory in selenium Chrome Capabilities?

For Chromedriver try out with:

String downloadFilepath = "/path/to/download";
HashMap<String, Object> chromePrefs = new HashMap<String, Object>();
chromePrefs.put("profile.default_content_settings.popups", 0);
chromePrefs.put("download.default_directory", downloadFilepath);
ChromeOptions options = new ChromeOptions();
options.setExperimentalOption("prefs", chromePrefs);
DesiredCapabilities cap = DesiredCapabilities.chrome();
cap.setCapability(CapabilityType.ACCEPT_SSL_CERTS, true);
cap.setCapability(ChromeOptions.CAPABILITY, options);
WebDriver driver = new ChromeDriver(cap);

Note:- Use File.separator to handle slashes, it will put syntax as per os it is executing the code. In windows you need to use \\ for path while if you are using linux or mac then use //

Hope this helps. :)

For Python users who see this page -- here's how I set the download directory in Python Selenium (this is just the Python version of Shubham's accepted answer):

def newChromeBrowser(headless=True, downloadPath=None):
    """ Helper function that creates a new Selenium browser """
    options = webdriver.ChromeOptions()
    if headless:
        options.add_argument('headless')
    if downloadPath is not None:
        prefs = {}
        os.makedirs(downloadPath)
        prefs["profile.default_content_settings.popups"]=0
        prefs["download.default_directory"]=downloadPath
        options.add_experimental_option("prefs", prefs)
    browser = webdriver.Chrome(options=options, executable_path=CHROMEDRIVER_PATH)
    return browser