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Having issues using ajax to reload captcha

Ajay Menon

Joined: Jun 06, 2011
Posts: 1

I am using SimpleCaptcha in my application. The captcha image changes for every new request.

Now i am trying to validate captcha using AJAX and when the validation is successful i will go ahead and submit the form or else i will need to reload the CAPTCHA.

The validation works fine but since the request doesnt change the CAPTCHA also remains the same.

When manual page reloads happens its rendering a CAPTCHA byt AJAX refresh doesnt render a new one.

Is there a way to create a new request in JAVA or AJAX everytime i validate or is there any other solution??

Karthik Shiraly

Joined: Apr 04, 2009
Posts: 874

If you have an img element to display the captcha, then the key to refreshing its image is to change its src attribute to something different.
If src is not changed, a browser would display the cached version of that URL, and you'll see the same image every time which is not what you want.
But if src is changed, a browser would then asynchronously and automatically make a new request to that changed URL, and display whatever image bytes it receives based on the response MIME type.

One simple way to change src attribute without changing the servlet behind that URL is to add current time as a query parameter on each request.
Your client side javascript should be something like:

The http://your_app_url/ is the URL for SimpleCaptchaServlet (or your custom captcha generating servlet) which responds with image bytes with "image/png" MIME type. The t query parameter can be ignored on server side - its purpose is just to vary the URL.
I agree. Here's the link:
subject: Having issues using ajax to reload captcha
jQuery in Action, 3rd edition