Just wanna to know whether it is possible to change the JSP custom tag's attribute dynamically with Javascript? I want to change the attribute value as I change the value of the text input in a html form.
No. Think about it for a minute. The custom tags, along with any other JSP mechanisms on the page, are executed on the server in order to format an HTML page to send to the browser. Once there, the user interacts with the page which will trigger whatever Javascript you might have.
Once the page gets to the browser where your Javascript can execute, there's no JSP, no custom tags, no any of the server-side mechanisms -- just a plain old vanilla HTML page.