Set array values in javascript from JSTL code

Question

I have a code that looks like this:

In AnalyzeUserClient.jsp:

<c:set var="arrayList"><%= (ArrayList<String>)request.getSession().getAttribute("arrayList") %></c:set>
var sessionId = [];
<c:forEach items=${arrayList} var="id">
sessionId.push("${id}"); // add them one at a time, assuming string values
</c:forEach>

However,this line:

    sessionId.push("${id}");

does not seem to be passing the values into the array "sessionId" (I viewed the source code on browser).So the question is,what can I do to pass the values into the array?

EDIT:I just realised that there are some problems as JSTL is server-side and JavaScript is client-side.So is there a workaround on it?

Regarding your edit about server-side working together with client-side, if the intention is to produce JS that populates the sessionId array and then use it only on the client-side then that doesn't matter. (It only becomes a problem if your server-side code tries to use the array too.) You should be able to use server-side code to output JS that populates an array - though I'd consider structuring it in a way that puts the values directly in the array literal [] rather than using .push(). — nnnnnn
– nnnnnn, Commented Nov 2, 2012 at 6:36
I tried doing: "sessionId["${id}"];" as well,but it is still not working.Is there another way to resolve this? — Marcus Dryice Koh
– Marcus Dryice Koh, Commented Nov 2, 2012 at 6:41

JB Nizet · Accepted Answer · 2012-11-02 07:30:07Z

8

Don't mix EL and scriptlets. In fact, forget about scriptlets completely:

var sessionId = [];
<c:forEach items="${sessionScope.arrayList}" var="id">
    sessionId.push("${id}"); 
</c:forEach>

Note though that this will generate invalid JavaScript if one of the IDs happens to contain a double quote. So you'd better JavaScript-escape the IDs before, in your controller. And I would suggest a completely different approach: serialize the list of IDs to a JSON string in your controller, and store this JSON string in request attribute. The JSP page will just need

var sessionId = ${jsonEncodedSessionIds};

which will translate to the following generated code:

var sessionId = ["id1", "id2"];

answered Nov 2, 2012 at 7:30

JB Nizet

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7 Comments

Marcus Dryice Koh Over a year ago

On the browser the line:"sessionId.push("${id}");" becomes "sessionId.push("");",is it related to the problems of server and client-side coding?

JB Nizet Over a year ago

No. It just means that the session ID stored in your list is null or is an empty string.

Marcus Dryice Koh Over a year ago

If that is the case,why does the browser unable to read the JSTL array values into the javascript array?

JB Nizet Over a year ago

I don't understand your question. sessionId.push("") is valid JavaScript. It adds an empty string to the sessionId array.

JB Nizet Over a year ago

It does add the values of the JSTL list. But this list contains a null element or an empty string. If it shouldn't contain that, then you have a bug in the Java code which populates this list.

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