As webdriver does not support direct any function to verify page response code. But using "WebClient" of HtmlUnit API we can achieve this.

Html unit API is GUI less browser for java developer, using WebClent class we can send request to application server and verify response header status.

Below code, I used in my webdriver script to verify response 200 of web application

String url = "http://www.google.com/";
WebClient webClient = new WebClient();
HtmlPage htmlPage = webClient.getPage(url);

//verify response
Assert.assertEquals(200,htmlPage.getWebResponse().getStatusCode());
Assert.assertEquals("OK",htmlPage.getWebResponse().getStatusMessage());

If HTTP authentication is required in web application use below code.

String url = "Application Url";

WebClient webClient = new WebClient();
DefaultCredentialsProvider credential = new DefaultCredentialsProvider();

//Set some example credentials
credential.addCredentials("UserName", "Passeord");
webClient.setCredentialsProvider(credential);

HtmlPage htmlPage = webClient.getPage(url);

//verify response
Assert.assertEquals(200,htmlPage.getWebResponse().getStatusCode());
Assert.assertEquals("OK",htmlPage.getWebResponse().getStatusMessage());   _{Your Comment}