Generating a screen capture on exception thrown with Selenium 2

Recently, someone asked how to have Selenium 2 (WebDriver) create a screen capture if an exception is thrown. Here is how you do it...

Let's say you have the code:

WebDriver driver;

    @Before
    public void setUp() {
        driver = new FirefoxDriver();
    }

and you want to change it so the test cases will generate a screen capture file when an exception is thrown. Here is the first change:

WebDriver driver;

    @Before
    public void setUp() {
        WebDriverEventListener eventListener = new MyEventListener();
        driver = new EventFiringWebDriver(new FirefoxDriver()).register(eventListener);
    }

The second change is to create the MyEventListener class. The MyEventListener class will be:

public class MyEventListener implements WebDriverEventListener {
    // All the methods of the WebDriverEventListener need to
    // be implemented here. You can leave most of them blank.
    // For example...
    public void afterChangeValueOf(WebElement arg0, WebDriver arg1) {
        // does nothing
    }

    // ...

    public void onException(Throwable arg0, WebDriver arg1) {
        String filename = generateRandomFilename(arg0);
        createScreenCaptureJPEG(filename);
    }
}

The MyEventListener class will have 15 methods, including the two examples I have given here. The main method that you must implement if you want screen captures whenever an exception is thrown would be the onException method.

The biggest trick for this method is generating a unique filename for each exception. First thought is that the filename could be in the format "YYYY-MM-DD-HH-MM-SS.jpg". Unless you get two exception in one minute this will work okay. Unfortunately, it will be hard to figure out what the exception was unless you kept some sort of log in the code execution. You'll also have to waste time figuring out which exception goes with which date/time.

Personally, I'd use the format "YYYY-MM-DD-HH-MM-SS-message-from-the-throwable-argument.jpg". Selenium tends to throw multiple line exception messages. So you could take the first line of the message, change characters which are illegal for your file system and change them to underscores. You could also have something to set the location of the screen capture files and prepend that to the filename.

Here is the code I came up with in 2 minutes:

private String generateRandomFilename(Throwable arg0) {
        Calendar c = Calendar.getInstance();
        String filename = arg0.getMessage();
        int i = filename.indexOf('\n');
        filename = filename.substring(0, i).replaceAll("\\s", "_").replaceAll(":", "") + ".jpg";
        filename = "" + c.get(Calendar.YEAR) + 
            "-" + c.get(Calendar.MONTH) + 
            "-" + c.get(Calendar.DAY_OF_MONTH) +
            "-" + c.get(Calendar.HOUR_OF_DAY) +
            "-" + c.get(Calendar.MINUTE) +
            "-" + c.get(Calendar.SECOND) +
            "-" + filename;
        return filename;
    }

The final part is the code to actually generate the file. This is standard Robot stuff. Here is the code I whipped together a few projects back:

private void createScreenCaptureJPEG(String filename) {
  try {
   BufferedImage img = getScreenAsBufferedImage();
   File output = new File(filename);
   ImageIO.write(img, "jpg", output);
  } catch (IOException e) {
   e.printStackTrace();
  }
 }
 
 private BufferedImage getScreenAsBufferedImage() {
  BufferedImage img = null;
  try {
   Robot r;
   r = new Robot();
   Toolkit t = Toolkit.getDefaultToolkit();
   Rectangle rect = new Rectangle(t.getScreenSize());
   img = r.createScreenCapture(rect);
  } catch (AWTException e) {
   e.printStackTrace();
  }
  return img;
 }

And that is it. Whenever an exception is thrown a file will be generate.