Combining JSP servlets and Javascript

Question

I have been working with ASP.NET for a few years and am now working on a project using JSP, Struts, and Java so I am fairly new to this.

I have a for-loop in a JavaScript function that looks something like this:

<% int count=0; %>
for(i = 0; i < arrayCount; i++){
   jsArray[i] = <%= myBeanArrayList.get(count) %>;
   alert("i = " + i + "count = " + count);
   <% count++; %>
}

The count variable doesn't increment even if I use <% count = count + 1 %>. I don't understand why that piece of code doesn't do as I want inside the loop. Does anyone have any suggestions on how I can increment the count for the JSP Bean?

Mixing JS and code behind like this is not good practice (in any language). — Timeout
– Timeout, Commented Feb 10, 2012 at 0:24

score 2 · Accepted Answer · 2012-02-10 00:36:49Z

2

That's because you are mixing things.

Your loop is in javascript and the variable count doesn't exists there (beacuse it's java)
You incremented count once, just in <% count++ %>

So if you change to use the loop inside java, the count can work just fine. For example:

<% for( int i = 0; i < ???; i++ ) { %>
 alert('<%= i %>');
<% } %>

But it's better separate your javascript from JSP. This can be a pain to mantain.

edited Feb 10, 2012 at 0:36

answered Feb 10, 2012 at 0:29

user800014

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5 Comments

duffymo Over a year ago

What an ugly, awful thing scriptlet code in a JSP is. No one should ever use it again.

user800014 Over a year ago

Yes it is. But it's just a example to Jared understand why his code not work.

user800014 Over a year ago

@duffymo so post an answer with that. I was focused just on his problem and really don't think about recommending something better.

iJared Over a year ago

ugly yes... but this was the solution :p

iJared Over a year ago

this is the one that worked for what i needed for now however i will look into some of the other answers later and try to rework it...

Mike C · Accepted Answer · 2012-02-10 00:36:59Z

1

I kind of agree with b1naryj, but you could try doing the looping in the jsp, and just write the array assignments in javascript, something like:

<% 
for(i = 0; i < arrayCount; i++){
   %>jsArray[<%i%>] = <%= myBeanArrayList.get(i) %>;
<%}%>

It is ugly, tho...

answered Feb 10, 2012 at 0:36

Mike C

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Comments

duffymo · Accepted Answer · 2012-02-10 00:43:26Z

1

No one should be using scriptlet code in JSPs. It's a late 90s idiom that has been found to be ugly, brittle, and hard to maintain. Model-2 MVC has swept the field.

You should concentrate on doing things on the server side. If you must write JSPs, use JSTL.

I think the current best practice is to use HTML, CSS, and JavaScript. Get data from services on the server side using HTTP GET/POST or AJAX calls.

answered Feb 10, 2012 at 0:43

duffymo

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1 Comment

iJared Over a year ago

I agree unfortunately I'm not the guy who wrote the original programming and am currently the low man on the todem pole so it will take some time before I have an influence on how to implement the code... plus I beleive we have restrictions as to what technologies we are able to utilize.

gilly3 · Accepted Answer · 2012-02-10 01:00:58Z

0

You are only looping on the client, not the server. The server code only gets executed once. So, for every iteration of the JavaScript loop, you are using the same value - myBeanArrayList.get(0). View source to look at the generated HTML code and that will probably help to clarify the problem.

Edit: Instead, use server-side code to build a JavaScript array literal. I don't really know JSP, and my Java is a little rusty, but wouldn't this work?

var jsArray = <%= new JSONArray(myBeanArrayList) %>;

edited Feb 10, 2012 at 1:00

answered Feb 10, 2012 at 0:28

gilly3

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4 Comments

iJared Over a year ago

ahhhhhh... the pop-up window I was working on wouldn't allow right-clicks or have a menu bar. Once I activated the menu bar and did a view source.. now I see what happens...

nnnnnn Over a year ago

@Jard - Yes, "View Source" is a useful tool when starting with this stuff. You just need to get used to the idea that all server-side code is executed before the page is sent to the browser.

iJared Over a year ago

yes its tough to get used to .. I am so used to asp.net web forms and using code behinds .. this mixing code, javascript, scriplets and html on a single page is mind boggling...

iJared Over a year ago

this might be the better route for those out there reading this post. I will update at a later time if I am able to implement this...

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