How to use JSP tags in JavaScript?

Question

How to use JSP tags in JavaScript file?

Is there any way?

Answer 1

JSP is a view technology which runs at the server side which you can use to write template text like HTML/CSS/JS in. You can use JSP taglibs and EL to control the page flow and output dynamically using Java code. This also concerns the JavaScript content/output. Once JSP has run, it basically produces a HTML page and sends it to the client side. You can use JSP to dynamically output back-end data as if it are JavaScript variables. For example:

<script>
    var foo = '${someBean.someProperty}';
</script>

Once the HTML page (with CSS/JS inside) has arrived at the client side (rightclick page and view source, you won't see any line of Java/JSP code), then the HTML will start to be interpreted, the CSS will start to be applied and the JS will start to be executed. There's no means of Java/JSP code at the client side. If you view the generated source in the client, the above example would now look like:

<script>
    var foo = 'somePropertyValue';
</script>

This way JavaScript has just instant access to server-side variables.

Now the other way round; the only way to let JavaScript access/invoke Java/JSP code is to actually send a HTTP request to the server side. This can be done several ways: doing a window.location to do a synchronous GET request, or doing a form.submit() to do a synchronous GET or POST request, or doing a XMLHttpRequest#send() to do an asynchronous request (also known from Ajax).

Alternatively you can also just let JavaScript set a (hidden) input field of a form so that it "automatically" get taken with the form submit whenever the user submits the form. Either way, the Java/JSP code at the server side will then be able to access JavaScript-controlled values the usual request parameter way.

To learn more about the wall between Java/JSP and JavaScript you may find this article useful.

Answer 2

I have wondered about this when I have values in my session or context I wanted exposed in the client side. I create a jsp file with javascript mime type which just include global variable values. Which I then include at the top of my page and reuse the values where necessary.

for eg:

**globalVar.jsp** 

var ctxPath = "<%=request.getContextPath()%>";

**script.js**

ajaxURL = ctxPath + "/path/to/call?param=value";

You can even namespace this as outlined here