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Passing JSP data to Java class and vice versa on button click

I am fairly new in JSP and I am trying to figure out how to pass data entered in the form on a JSP page to the java class and send this data back to the JSP page on click.
My index.jsp looks a bit like this:
<%# page import="mypackage.*" %>
<% myClass c = new myClass();
c.setString("String"); %>
<p>This is a test: <%= c.getString(); %></p>
The above code will output "String". I can access my class with no problems if I set the value on page load. I tried using servlets after some research. I modified my form to add the servlet "testServlet" on form action:
<form method="POST" action="testServlet">
Then on the doPost() method in testServlet I added in this:
String myString = request.getParameter("myString"); //myString is also the name of my textbox
System.out.println("Entered string: " + myString);
However, I am clearly missing a crucial part of the flow of how this should work and I am most probably wrong with this one as well as all the form does after I press submit is redirect to testServlet so I get the error that the resource is not available since it isn't a JSP/html page.
So my questions are, how exactly can I pass data from JSP to java and vice versa? Also, is there a possible way to do this without servlets? And what are good tutorials/examples for studying JSP and its behavior such as passing data? Please help.
After some more research, I am now able to transfer data set on index to detail using jsp:useBean however, as I've read in all the forums I've visited, servlets should be used to handle this but this really confused me more as a beginner so I really want to figure out what I'm missing here.
I've made sure that the servlet is registered on web.xml and I didn't change anything in there.
Update: I've tried re-creating the project from scratch and somehow managed to make the servlet work. As it turns out, I was missing something on the doGet() method. But now my question stands, is there a way to process the form without using servlets or page import in the JSP file? I was shown a sample code that didn't use servlets or page imports. I did take notice at tag.

use the java beans with getters and setters for there class member variables.

Refeshring JSP page in Javascript

I am trying to refresh the JSP page after certain operations, I am using DWR to be able to use my classes in Javascripts in the JSP files so I have this code:
function removeDN(numplanindex){
DBOps.removeDN(numplanindex);
relaod(true);
}
the above code will break the removeDN() and it would not refresh the page, I have also tried window.location.reload(true) and document.location.reload(true).
I am not sure about the difference as I barely know any Javascript but according to everything on google this should work. I am wondering if anybody know what is wrong with what I am doing wrong.
Thanks

It should be reload(true) instead of relaod(true)
Also see http://www.w3schools.com/jsref/met_loc_reload.asp

Java Custom tag containing generated JSTL : not interpreted

I have a custom tag that has no body at all. I'm trying to programmatically replace the empty body with, for simplicity's sake,
[<c:out value="SUCCESS!"/>]
The goal is to see "[SUCCESS!]" displayed by the JSP which uses the tag, but all I see is "[]" and if I look at the generated source code, I can see that the c:out statement is written on the page between the brackets, but not interpreted.
Is there a common way to achieve this ? The final goal will be to use other custom tags instead of the "c:out" tag. The tags/content will come from a database.
I tried different techniques with SimpleTagSupport and BodyTagSupport but none of those were successfull. In fact I'm not sure if it is technically possible to do it, since, the tag has already been interpreted at that time.. But then how should this be done ?

Server tags (like your custom tag or JSTL tags) get transformed to Java code when the JSP is translated into a servlet. For example, the following JSP code:
<c:out value="FooBar" />
gets translated to something like this inside the servlet:
....
OutTag outTag = (OutTag) tagHandlerPool.get(OutTag.class);
outTag.setPageContext(pageContext);
outTag.setParent(null);
outTag.setValue(new String("FooBar"));
int evalOut = outTag.doStartTag();
....
In your custom tags you can call other Java classes/methods and can write HTML code (not JSP code) to the response.
The [<c:out value="SUCCESS!"/>] is not interpreted because at this level it's just a string that gets written directly to the response.

JSP renders weird HTML

I'm getting a very strange behaviour in one of my JSP pages. It looks like it doesn't render the complete HTML. It looks like this:
<html>
...
<table>
...
</table>
<div id=
So the last line is exactly what you get when the page is rendered. Furthermore, when you do a view source you get exactly the same. This page doesn't have any fancy logic ... there are no javascript erros, no missing closing tags, etc ...
Is there any sort of page limit for a jsp page?
A bit more background: This page works just fine in a WIN2K server running Tomcat 5.5. I'm upgrading this app to run under a server with WIN2008 + Tomcat 6.0. That's where I get the error ...
Any help is appreciated.

Is there any sort of page limit for a jsp page?
AFAIK, no.
I think that the most likely cause is that your JSP is throwing an exception. Check the Tomcat logs, and look at the JSP at the point after the last HTML that was output.
EDIT
#Adam Crume says: "The exception may be thrown at a point further down from where the output stops, due to buffering."
True. As a temporary hack to get around this, you could surround the JSP's content with a try / finally, and flush the output stream in the finally block.

Is there any sort of page limit for a jsp page?
Yes, there is. It's about 64KB. JSP's are basically compiled into a large try statement. In Java, there's a 64KB limit for try statement. But if you exceed this, it would have prouced a different exception.
This problem at least indicates that you're using scriptlets in the JSP. This is a bad practice. Whenever an exception occurs halfway a JSP page, you'll get a blank or halfbaked page without information about the problem. Don't execute business stuff in JSP, but in a preprocessing Servlet.

How to JSP display multiple page with one layout (Example index.jsp?page=about display about.jsp)

I new in JSP, i have a problem with JSP
in php i use
$page=$_GET["page"]
for display multiple page for one layout it mean i have index , it display layout and when i click on menu go to about us the index url = index.jsp?page=about
in PHP when i declare $page above and next step i do
Switch($page){
case 1:about
include 'aboutus.php'
case 2:news
include 'news.php'
}
How can i do it ?
How jsp can do the same way php to display multiple page in 1 layout

Use jsp:include.
<jsp:include page="/WEB-INF/${param.page}.jsp" />
And pass ?page=news or ?page=about, etc as parameter. The ${param.page} prints the outcome of request.getParameter("page"). You can prevent direct access to JSP files (by entering URL in browser address bar) by placing JSP files in /WEB-INF folder.
See also:
Basic JSP/Servlet tutorials
Hidden features of JSP/Servlet
How to avoid Java code in JSP

nowadays you use "templates" of Java Server Faces (JSF) for this approach. When you use JSP, you actually don't use the same concept as in PHP. You'd better use the MVC concept. But to answer your question, you could probably achieve this with the include tag http://java.sun.com/products/jsp/tags/11/syntaxref1112.html and control it with JSTL:
http://www.java2s.com/Code/Java/JSTL/JSTLiftag.htm