Selenium: getPageSource() returns previous pages' source

Question

I'm logging into the page using this function:

    public static void login() {
       driver.get(url);
       driver.findElement(By.name("username")).clear();
       driver.findElement(By.name("username")).sendKeys("username- login");
       driver.findElement(By.name("password")).clear();
       driver.findElement(By.name("password")).sendKeys("password");
       driver.findElement(By.name("submit")).click();
       driver.manage().timeouts().pageLoadTimeout(30, TimeUnit.SECONDS);
   }

The login is successful and now i'd like to verify this by checking for certain elements on the landing page as follows:

    public static void testLogin(WebDriver driver) {
       String pageSource = driver.getPageSource();
       //Assert.assertTrue("Login was not successful!", pageSource.contains("Welcome to the page!"));
       System.out.println(pageSource);
}

Everything works except for the fact that when i display the source code on the console, it is the source code of the login page (previous) and i'm hence the Assert is false.

Can anyone point me in the right direction?

Edit

I have accepted the answer from the_coder because it led me to this solution: I used WebDriverWait to wait until a specific element is present on the page before saving the source code into a String.

 WebDriverWait wait = new WebDriverWait(driver, 10);  
 wait.until(ExpectedConditions.presenceOfElementLocated(By.xpath("//*[contains(.,'Welcome to the page!')]")));

Answer 1

You may be getting the previous page source code because the getPageSource() method is called before the page arrives to the page you want.

One thing I would like to suggest is before getting the pagesource of the webpage check whether you have navigated to the correct page like:

public static void testLogin(WebDriver driver) {
     if(driver.getCurrentUrl().equals("<expectedPageURL>"))
     {
       String pageSource = driver.getPageSource();
       Assert.assertTrue("Login was not successful!", pageSource.contains("Welcome to the page!"));
       System.out.println(pageSource);
     }
     else
     {
         System.out.println("Not navigated to the correct page");
     }
  }