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how to use the same object instance in main jsp page and jsp:included files as well?

Answer 1

A:

I think this is possible you could pass a parameter like this:

<jsp:include page="include1.jsp" />  
  <jsp:param name="counter" value="<%=counter%>" />  
</jsp:include>

Plus you have to define the counter as a jsp declaration like this i think:

<%! int counter =0; %>

kukudas 2010-10-15 16:53:48

This looks like a very simple solution - I think I was missing JSP's 'static' concept. I will give this a go and report back. Thank you for your response.

Joel 2010-10-18 12:13:33

It won't make it static, but it will make it an instance variable instead of a local variable. Instance variables are however shared among **all requests** throughout the entire webapplication. You don't want to have that, it would only lead to unexpected results when multiple users access the same JSP simultaneously.

BalusC 2010-10-18 13:02:57

BalusC is right. It's a jsp declaration which will result in an instance variable. I also think the solution suggested by him is more appropriate and easier to implement.

kukudas 2010-10-18 13:15:03

I also read some stuff that suggested this might not be a 'modern' approach. I have looked into another solution.

Joel 2010-10-21 14:27:16

Answer 2

A:

Just store it in the request scope. JSTL's c:set is helpful in this.

<%@ taglib uri="http://java.sun.com/jsp/jstl/core" prefix="c" %>
...
<c:set var="counter" value="0" scope="request" />
<jsp:include page="include1.jsp" />
<jsp:include page="include2.jsp" />
<jsp:include page="include3.jsp" />

Then in each of the include files do as follows to increment it:

<c:set var="counter" value="${counter + 1}" scope="request" />

or even statically

<c:set var="counter" value="3" scope="request" />

BalusC 2010-10-16 03:08:01

Thank you for the response. I hadn't thought of looking to the JSTL for a solution. I will try this out!

Joel 2010-10-18 12:57:27

Answer 3

A:

I solved this problem by passing my value in the request object.

It looks like this:

My main.jsp says:

<% int counter = 0; 
   request.setAttribute("counter", counter);
%>

<jsp:include page="include1.jsp">
   <jsp:param name="counter" value="<%=request.getAttribute("counter")%> />
</jsp:include>

<jsp:include page="include2.jsp">
   <jsp:param name="counter" value="<%=request.getAttribute("counter")%> />
</jsp:include>

<jsp:include page="include3.jsp">
   <jsp:param name="counter" value="<%=request.getAttribute("counter")%> />
</jsp:include>

and my 'include' jsps look like this:

<%
   Integer counter = 
      Integer.valueOf(request.getParameter("counter"));
%>

   <!-- do my stuff, sometimes manipulating the 'counter' Integer object -->

<%
   request.setAttribute("counter", counter);
%>

You can see how this works. The main page passes the value of the counter object as a param to the first includeX.jsp, which pulls the param out of the request and uses it. Then at the end of the includeX.jsp it sets the current value of the counter in the request attributes. When the main.jsp picks it up again it pulls the value from the request attributes to hand in to the next includeX.jsp as a param again.

At one point I did have it implemented /all/ using request.get/setAttribute calls rather than the stuff, but it seemed to indicate the flow better to pass it as a parameter rather than pull it from the request object. I don't really know the pros/cons of either approach but this is working for me now.

Thanks for the help everyone, even though I implemented in a totally different way than suggested.

Joel 2010-10-21 14:26:14

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how to use the same object instance in main jsp page and jsp:included files as well?

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