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Retrieving Servlet info from non-form parts

I am trying to create an application that reads JSON strings.
Right now: I can input a JSON string through Java, write it to an HTML document and have a JavaScript application read it; which then parses it and writes it to the same HTML application. I need to know how, using Java, to read the HTML that it gets written to so I can use that data. It is important to note this HTML file is all generated by code so there is no actual text file to read.
I realize this is a roundabout way of doing it, but up until this point it has worked. My question is simple: How can I read an HTML page in a part that is not in a <form> through either regular Java or Servlet.

You can do that only by parsing the HTML in Java. And, there are some open source libraries that does this job for you.
Here is one that you can use.
http://jsoup.org/

How to include a file in Javascript and Jsp?

Ok,i know in Php you can use include for a Php file...for example...
include("array.php");
Is there a way to do this in Javascript and Jsp?
From what i read i cant use for example include("array.javascript"); or include("array.jsp");
I want to load the array from a different file and i know how to do it with Php,but not with Javascript or Jsp. Any help?

I think you are a bit confused, JSP is an XML-based language executed at the server side that gets transformed into Java the first time is processed by the servlet container (server) whilst JavaScript is an interpreted language executed by the user's browser, not the server. PHP is also executed at the server-side and that include function has nothing to do with JavaScript.
Now, to port that behaviour to JSP you would use a JSP tag, more specifically, the <jsp:include /> tag:
<jsp:include page="array.jsp" />
But if what you are trying to is to link your JSP with a JavaScript file then you should use a better option which consist of using the standard HTML <script> tag:
<script type="text/javascript" src="array.js" />

Referencing ASPX controls from an External JS file

I have a question. I have a aspx control (for e.g textbox). I reference it using document.getElementById('<%=textbox.ClientID%>').value. When I have the code in the same aspx file it works. But as soon reference it from an external file (example MyJSFunctions.js), I cannnot. I get an error saying "the object does not exist or it is null"
I have included the name of the js file like
I did this because I like having all my js functions in a seperate file nad doing this also reduces the load overhead.
Why is this happening? Can I accomplish the same using jquery?

You will need to parametise your Javascript to accept the desired argument, then pass the inline ASP.NET script within the server-side page or control as the value of such. This will allow the engine to render the inline code appropriately.
It happens because the server renders your pages (not in the sense of a browser rendering HTML, but rather the ASP.NET engine making transformations to turn your .NETified web mark-up into standard web mark-up) prior to pushing them down to the client - this will only happen for "registered" types, and that doesn't (and shouldn't) include Javascript files (although you can technically register items to handle, unless you have a bespoke module to handle compilation of inline scripting among Javascript, then it would err anyway.)
jQuery essentially being something of a Javascript framework, you're in the same boat with that, so to speak.
As an example, consider the following...
Your script file:
function doSomethingJavascripty(withThisClientID) {
//do something with...
document.getElementById(withThisClientID).value;
}
Your ASPX page:
<script type="text/javascript" src="/path/to/script.js"><script>
<script type="text/javascript">
//call your function when appropriate...
doSomethingJavascripty('<%=textbox.ClientID%>');
</script>

One thing you could do is have the following Javascript code in your ASPX page:
var myTextbox = '<%=textbox.ClientID%>';
Then, in your external JS file (make sure this is after the above line), have:
document.getElementById(myTextbox).value
Another alternative is just hardcode in the ClientID into your code, but note you'll break it if you change the ID or parent container of that textbox control in the future.

how to add el code or jstl code through javascript

how to add el code and jstl code to the textbox generated dyanmically like ${fn:escapeXml(param.foo)} as value of textbox.

That's not possible. Webbrowser doesn't understand JSTL and EL code. It only understands HTML/CSS/JS code. This JSTL/EL code has to run in the webserver. Your best bet is to let JavaScript send an Ajax request to the server which in turn runs some JSP with JSTL/EL code and then returns the generated HTML response and finally let JavaScript display that HTML.
If your sole functional requirement is to HTML/XML-encode a JavaScript variable as fn:escapeXml() does for JSP, then head to the answers of this question: HTML-encoding lost when attribute read from input field.
Please note that there is no XSS risk as long as the data is stored fully client side. Once you send the data to server and the server stores it and redisplays it to another enduser, then there's means of a XSS risk. For that fn:escapeXml() in JSP can just be used since it's the server which redisplays it.

if you generate dynamically textbox using javascript, you have page at client side so now you have no chance to substitute EL resolved..

You can't do that. EL and JSTL get executed on the server. JavaScript gets executed on the client after that. JavaScript can't do anything to affect EL or JSTL.

Calling Java inside JavaScript Function

Please tell me if we can call java inside javascript function ?
<HTML><HEAD></HEAD><BODY>
<SCRIPT>
function getScreenDimension() {
<% System.out.println("Hiiiiiiiii"); %>
}
</SCRIPT>
<FORM>
<INPUT type="button" value="call Java method direct" onClick = "getScreenDimension()">
</FORM>
</BODY></HTML>

While the answer of "No" is technically correct based on the phrasing of the question. You may want to read up on AJAX. It is a way for javascript to make a request to your backend code (in this case Java).
Javascript is client side, meaning it is run by the user's browser. Java is running on your server. In order for the client side javascript to interact with the backend Java, you need to make a request to the server.

My question to you would be, "What are you trying to do, and what do you expect to see?".
You have to realize that there are two different execution contexts. The first is the JSP itself whose code is executed by the JVM on the server-side, and the second is the Javascript that is executed by the browser. So when the code goes to the browser, you'll see: So the System.out.println will cause Hiiiiiiiii to be printed to the server logs, but you won't see anything on the browser. In fact, the Javascript code on the browser will look like this:
function getScreenDimension() {
}
Which is not valid Javascript code. The code in the JSP is run before the Javascript gets run on the browser. So to "run" Java code, you need to make a request to your server either by posting the form or with an AJAX call. This will cause Java code in the appropriate servlet or controller, to run.
UPDATE
After glancing at your code, it appears that you want to call a Java method directly. This is not possible with your current code. You might want to read up on AJAX. This will point you in the right direction.

JSP runs on the server. It generates a document which the server sends to the browser. That is the end of the involvement of JSP in the process. The browser then parses the document and runs any JS.
You can include JSP in a script element, it just has to output valid JavaScript.
You cannot have JSP that runs in response to JavaScript, other then when JavaScript causes the browser to issue a new HTTP request (either setting location.href, submitting a form, adding an image, or using Ajax, etc)

I think you have lack of understanding of what is going on here. Anything in middle of <% %> is executed when the page is first requested. Anything in javascript is executed when the browser calls it. What you have will never happen and there is no way to make it happen. However, you can use AJAX to do something like this but that's a different question.

Yes, you can. Use JSP expressions <%= %>. Example:
<aui:script use="aui-datepicker">
AUI().use('aui-datepicker', function(A) {
new A.DatePickerSelect({
calendar : {
dates : [ '<%="1/1/1970" %>' ],
}
}).render('#myDatePicker');
});
</aui:script>

Yes, you can call Java from Javascript, both if you mean the Java-VM on the server and on the client; i assume you mean the client (the VM in the browser); take a look here:
http://www.apl.jhu.edu/~hall/java/Java-from-JavaScript.html

You can. In JSF you can use PrimeFaces' component p:remoteCommand, which would contain action method. Call that remoteCommand by its name from JS and the java method will get executed.
JSF Page
<p:remoteCommand name='rmt' action="#{bean.doWork()}"/>
In JavaScript
function callJava {rmt();}

Use JSP code
<%
// Respond to the application with 1) result, 2) update, and 3) updateid values
String result = "blablabla";
out.print(result);
%>