Develop Reference

Run selenium with cache on centos/linux

I'm able to run selenium on non GUI centos/linux machine in headless mode.
I have been trying to run it with cache enable by passing below chromeoptions arguments.
chromeOptions.addArguments("user-data-dir=~/.config/google-chrome");
It has started fine and identified elements till login page(which is first page) and couldn't identify any locators after that.
Is it the right approach to run cache enabled selenium run?

It's not that super clear when you mention about executing your tests with cache enabled. However, adding the argument user-data-dir is the canonical way to use a specific Chrome Profile.
You can find a couple of detailed discussions in:
How to open a Chrome Profile through Python
How to use Chrome Profile in Selenium Webdriver Python 3

Adding those options helps me to prevent crashes and errors on a linux remote machine
ChromeOptions options = new ChromeOptions();
options.addArguments(
"--disable-gpu",
"--headless",
"--window-size=1920,1200",
"--ignore-certificate-errors",
"--disable-extensions",
"--no-sandbox",
"--disable-dev-shm-usage",
"--hide-scrollbars",
"--allow-running-insecure-content",
"--disable-infobars",
"--ignore-certificate-errors");
Webdriver driver = new ChromeDriver(options);

Change proxy after starting chromedriver in java selenium

Is it possible to use proxy after starting chromedriver on the same browser?
EX:
I start chrome driver
Load website
Put in info
Use proxy
Click submit
I think i found some ways to do it in python and JS but im not sure how to convert it to java

As per Selenium's current implementation once you configure the WebDriver instance with the required Options and Capabilities and initialize the WebDriver session to open a Web Browser, you cannot change the capabilities runtime. Even if you are able to retrieve the runtime capabilities still you won't be able to change them back.
So, in-order to use a proxy you have to initiate a new WebDriver session.
here is #JimEvans clear and concise comment (as of Oct 24 '13 at 13:02) related to proxy settings capability:
When you set a proxy for any given driver, it is set only at the time WebDriver session is created; it cannot be changed at runtime. Even if you get the capabilities of the created session, you won't be able to change it. So the answer is, no, you must start a new session if you want to use different proxy settings.
You can find a relevant discussion in Set capability on already running selenium webdriver

You can use ChromeOptions class.
You can create an instance of ChromeOptions, which has convenient methods for setting ChromeDriver-specific capabilities. You can then pass the ChromeOptions
object into the ChromeDriver constructor:
ChromeOptions options = new ChromeOptions();
options.addExtensions(new File("/path/to/extension.crx"));
ChromeDriver driver = new ChromeDriver(options);
ChromeOptions options = new ChromeOptions();
// Add the WebDriver proxy capability.
Proxy proxy = new Proxy();
proxy.setHttpProxy("myhttpproxy:3337");
options.setCapability("proxy", proxy);
// Add a ChromeDriver-specific capability.
options.addExtensions(new File("/path/to/extension.crx"));
ChromeDriver driver = new ChromeDriver(options);

Creating Firefox profile and switching off the marionette

I am coming from Ruby background, I know how to do this in Ruby Selenium Binding, but I don't know how to do it Java Selenium Binding,
I have this code to create Firefox profile
FirefoxProfile firefoxProfile = new FirefoxProfile(pathToProfile);
WebDriver driver=new FirefoxDriver(firefoxProfile);
It works in selenium 2.53 but it's throws error in very recent selenium binding 3.11.0, Can anyone tell me what's the alternative?
And also I wanted to switch off the marionette to connect to Legacy Firefox driver, I can do this with the following code
DesiredCapabilities capabilities = DesiredCapabilities.firefox();
capabilities.setCapability("marionette", false);
WebDriver driver=new FirefoxDriver(capabilities);
But if I use the above line, then it gives the FirefoxDriver is deprecated. Can anyone guide me how to create profile as well as how to switch off the marionette?

Yes FirefoxDriver(desiredCapabilities) is deprecated.
Alternate way would be to go with options:
FirefoxOptions foptions = new FirefoxOptions(capabilities);
WebDriver driver=new FirefoxDriver(foptions);
Update : [In order]
FirefoxOptions foptions = new FirefoxOptions();
FirefoxProfile firefoxProfile = new FirefoxProfile(pathToProfile);
foptions.setProfile(firefoxProfile);
foptions.setCapability("marionette", false);
foptions.setBinary("C:\\Program Files\\Mozilla Firefox 52\\firefox.exe");
WebDriver driver = new FirefoxDriver(foptions);

To use an existing Firefox Profile for your Test Execution first you have to create a Firefox Profile manually following the instructions at Creating a new Firefox profile on Windows. Now you have to pass the Firefox Profile to a FirefoxOptions class object. Additionally as you would be using the Legacy Firefox Browser
you have to set marionatte to false through a DesiredCapabilities class object which you need to merge() into the FirefoxOptions class object as follows :
System.setProperty("webdriver.gecko.driver", "C:\\Utility\\BrowserDrivers\\geckodriver.exe");
ProfilesIni profile = new ProfilesIni();
FirefoxProfile testprofile = profile.getProfile("debanjan");
FirefoxOptions options = new FirefoxOptions();
options.setProfile(testprofile);
DesiredCapabilities dc = new DesiredCapabilities();
dc.setCapability("marionatte", false);
options.merge(dc);
WebDriver driver = new FirefoxDriver(options);
driver.get("https://www.google.com");
Update
I am not sure about your usecase and why you want to use Legacy Firefox Driver. But as per the GitHub discussion Unable to Start Firefox Using the Legacy Driver on a 3.5.3 Grid #jimevans clearly mentions :
The legacy Firefox driver won't work with Firefox 53 or so. You might get the browser to launch, but the language bindings will be entirely unable to communicate with the driver (because Firefox will refuse to load the browser extension that is the legacy Firefox driver).
#barancev also mentions :
A binding should not pass OSS capabilities in W3C-compliant parts of payload, in "capabilities" block. They are allowed in "desiredCapabilities" block only. Perhaps, Mozilla broke Selenium compatibility in Firefox 48 in release channel, but restored it in version 52 in esr channel. It was unexpected, but it's true.
It's all upto you to take a informed descission.

Is there a way to clear session data to ensure a clean session is initiated each time?

For IE you would use capabilities like this:
DesiredCapabilities cap = new DesiredCapabilities();
cap.setCapability(InternetExplorerDriver.IE_ENSURE_CLEAN_SESSION, true);
and possibly in combination with
driver.manage().deleteAllCookies();
How could this be achieved using Chrome and ChromeDriver?

While we work with Internet Explorer Driver we use the field IE_ENSURE_CLEAN_SESSION
IE_ENSURE_CLEAN_SESSION
As per the JavaDocs IE_ENSURE_CLEAN_SESSION is the Capability that defines whether to clean or not browser cache before launching Internet Explorer by IEDriverServer and is configured as follows :
DesiredCapabilities cap = new DesiredCapabilities();
cap.setCapability(InternetExplorerDriver.IE_ENSURE_CLEAN_SESSION, true);
Now let us have a look at GeckoDriver which follows the WebDriver Spec.
GeckoDriver / moz:profile / rust_mozprofile
If you have a closer look at the geckodriver logs closely you will observe that each time geckodriver is called a new moz:profile is scopped out and the details of rust_mozprofile occurs in the following line:
Marionette CONFIG Matched capabilities: {"browserName":"firefox","browserVersion":"56.0","platformName":"windows_nt","platformVersion":"6.2","pageLoadStrategy":"normal","acceptInsecureCerts":false,"timeouts":{"implicit":0,"pageLoad":300000,"script":30000},"rotatable":false,"specificationLevel":0,"moz:processID":5848,"moz:profile":"C:\\Users\\AtechM_03\\AppData\\Local\\Temp\\rust_mozprofile.OfFuR9ogm33d","moz:accessibilityChecks":false,"moz:headless":false}
This log clearly indicates that Marionette scoops out a new "moz:profile":"C:\\Users\\AtechM_03\\AppData\\Local\\Temp\\rust_mozprofile.OfFuR9ogm33d" and this configuration is handled by the WebDriver instance i.e. the GeckoDriver.
You can find a more detailed discussion on moz:profile in Is it Firefox or Geckodriver, which creates “rust_mozprofile” directory discussion.
ChromeDriver
ChromeDriver which is following the same WebDriver Spec does abides (will be abiding) by the same suite.
Incase you are using any stored FirefoxProfile or ChromeProfile, WebDriver will pick up the existing profile where the Stored Browser Configurations are picked up for reuse.
driver.manage().deleteAllCookies();
Irespective of New/Existing FirefoxProfile or ChromeProfile if you add the line :
driver.manage().deleteAllCookies();
Only the cookies gets deleted only to be get restored back to support the Active Browser Session

Selenium Webdriver (Java) connect/interoperate with a Firefox extension/plugin

i am looking for a way to connect out of the Selenium Webdriver to a Firefox extension/plugin.
I want to start a function from the firefox extension out of the api of the selenium Webdriver. Could this be possible?
I know that i can call javascript code which is inside a page, but not inside a firefox extension.
If it is not possible with selenium webdriver, is there another way to connect, maybe with java?
Thanks a lot for your help!

One of way, how you could do this, is:
Create firefox profile and name it somehow you know what it is. e.g. SELENIUM
Install addon to this profile. In general, make that profile suitable for the tests.
When initializing the Webdriver:
ProfilesIni allProfiles = new ProfilesIni();
FirefoxProfile desiredProfile = allProfiles.getProfile("SELENIUM");
WebDriver driver = new FirefoxDriver(desiredProfile);