ArrayList gets duplicate values in JSP

[Sree Mami]

Hi all

I have lots and lots of doubts in JSP/Servelts. I am happy to see this site members responding so quickly..



I am retrieving some values from database into a Drop down list box say "Employee" based on the value selected I am passing a query again to the database to get value into another Drop down list box. The problem is when the page refreshes after loading values into the second list box, first list box options gets doubled (Arraylist items gets duplicated and it gets populated as and when I refresh the screen) I have stored the value of the selected option into a session and passed that to the jsp page and cleared the ArrayList of first list box and now I got a new problem whenever page refreshes the first list box is empty (as I cleared the ArrayList at the end) how should I retain the values in the drop down list boxes without getting duplicate values for every screen refresh?

Even I am getting ArrayIndexOutofBound exception at some index position.

Please clarify as I am very new to JSP/Servlets..

Thanks a lot in advance.

[Ben Souther]

We would need to see your code in order to help you.

Before posting it, be sure to read:
UseCodeTags.

[Sree Mami]

 
My main JSP page: [B]MainForm.jsp[/B]
<%@ page import="java.util.*, mypackage.*" session="true"%>
<jsp:include page="loadComp.jsp"/>
<%!
   ArrayList depa=new ArrayList();
%>
<%
<select name="company" id="comp" accesskey="c" tabindex="1" style="width:184" onchange="loaddept()">
<option></option><%....//some code from loadComp.jsp... %>
</select>
<select name="department" id="deptmt" accesskey="D" tabindex="2" style="width:184">
              <option></option>
<%
depa=(ArrayList)session.getAttribute("DeptNames");
if(depa==null)
depa=new ArrayList();
if(depa!=null)
for(int i=0;i<depa.size();i++)   
{
 deptname=(String)depa.get(i);
%>
        <option 
<%if(request.getParameter("department")==null)
{%>
<%=""%>
<%}
else if(request.getParameter("department").equals(deptname))
{
out.println("selected");
}
%> value="<%=deptname%>"><%=deptname%></option>
    
<%  
}//for

%><%
session.removeAttribute("DeptNames");
%>
                </select>
 
%>
 
Controller JSP: [B]loaddept.jsp[/B]
 
<%@ page import="java.util.*, mypackage.*" session="true"%>
<%!
ArrayList depts=new ArrayList();
String select_cname=null;
WBean wb=new WBean();
%>
<%
System.out.println("In loaddepts.jsp file");
select_cname=(String)request.getParameter("company");
System.out.println("Company name for departments..."+select_cname);
depts=wb.getDepartments(select_cname);
System.out.println("Departments for company"+select_cname+"are"+depts);        
session.setAttribute("DeptNames",depts);

%>
<jsp:forward page="MainForm.jsp"/>
 

This is my code.. Where I am getting duplicate values in the array list which I am using to store values in the dropdown list box "department".

Can u please clarify!
[ July 20, 2006: Message edited by: Sree Mami ]

[Bear Bibeault]

Most likely a threading issue.

You used:

<%!
   ArrayList depa=new ArrayList();
%>    

which creates one instance of the array list which is shared amongst all instances of the JSP. Is that what you wanted?

[Sree Mami]

Thanks all!

I could resolve this issue. Actually whenever I am getting values from the database into the ArrayList, first I am clearing it so that the previous values will not exist anymore.

Once again thanks for your help!!!

[Bear Bibeault]

If you are still using the <%! %> notation to make your variable declarations, then you still have a serious problem with your JSP which will cause perplexing and miserable failures as soon as simultaneous access to the JSP takes place.

[Sree Mami]

Hi Bear Bibeault

I didn't get your point:

If you are still using the <%! %> notation to make your variable declarations, then you still have a serious problem with your JSP which will cause perplexing and miserable failures as soon as simultaneous access to the JSP takes place.

If I shouldn't declare variables in <%! %> what else should I do, to avoid the problem which you were discussing?

Can you explain me the problem declaring variables in "Declaration Tag" in detail!

[Bear Bibeault]

Using declaration scriplets creates instance variables which are shared with across all threads serving the JSP.

[Sree Mami]

Then, do u mean I should avoid declaring variables in <%! %> and use <% %> rather!

[Bear Bibeault]

Please use real words in your posts rather than "u".

In my opinion, if you're using JSP 2.0 you shouldn't be using scriptlets at all. But if you are going to employ scriptlets, avoid the use of declaration scriptlets for anything that's not intended to be shared across all threads.
[ July 22, 2006: Message edited by: Bear Bibeault ]

[Sree Mami]

Thanks a lot for your comments!

[Ben Souther]

Originally posted by Sree Mami:
Then, do u mean I should avoid declaring variables in <%! %> and use <% %> rather!

Yes.
Otherwise all requests to your servlet will share the same variable and you will have threading issues.