在CSS模板扩展中调用的Java方法中，将javascript变量用作参数

Question

I'm trying to pass a variable pulled from a javascript file as a parameter for a java method in a template expansion. The variable is the file path of an image I want to display on the web page. When I try to display the plain image, I can call it using

"${ImageUrl}"

which returns the whole file. However, the file is in an external filesystem, so what I want to do is call a method that can go fetch the correct file and handle that as necessary and pass the file path as the parameter in that method. However, when I call

"${getImage(ImageUrl}"

my java file reads ImageUrl as the text "ImageUrl".

Is there a way to call the method and pass in the correct javascript variable as a parameter?

Thanks

Answer 1

Keep in mind the basic physics of web apps: JavaScript in the browser can't directly call a method in Java code on the server. Furthermore, with Tapestry, when you have a template expansion (the ${...} syntax) in a template file, that expansion is first resolved on the server side before the HTML is sent to the browser, THEN your JavaScript runs in the browser.

You didn't provide enough information for the reader to know what the best solution is in your case. You could send info from JavaScript to the server-side web app via an AJAX call; or maybe the JavaScript should request a whole page render, passing the image name as a page activation context; or the JavaScript could just build the actual URL itself and create an tag on the fly. It all depends on your own preferences and requirements.

Answer 2

Javascript files are static, they can be downloaded once and cached by the browser. Rather than embedding dynamic variables in your js file, pass them in as a function argument