Recursion problem solved, question opened

[Nikola Milutinovic <Ni...@ev.co.yu>]

Hi all.

Some days ago I reported an error on JDBC and JSP in recursion. Just to remind everyone...

I had a JSP page make a JDBC connection to PostgreSQL database. The database contained a table which held a hierarchy (n-tree) and another that held "leaf nodes" (our company, it's organizational units and e-mail users). The JSP page is capable of displaying all e-mail users for a given org_unit, no problem there. Then I added option to display only partial HTML, just the portion of the table, with the idea to include it in another request. No problem there, either.

The problem occured when I tried to recursively include the same page in order to display the entire sub-tree for a given node. I was getting unexplicable error, mostly JDBC.

SOLUTION
-------------

I have tested a standalone Java, which worked and a local method inside JSP, which also worked!!! That led me to the source of the problem. The only difference between my attempt to do a recursive inclusion in a method (which worked) and recursive inclusion with <jsp:include> was in the placement of JDBC variables.

In case of the method, they were local to the method. In case of the <jsp:include> they were global for the page, inside <%!  %> section. Once I moved the declarations to the scriptlet <%  %> portion, it all started working.

So, this deosn't work in a recursion:

<%!
Connection conn;
Statement stat;
ResultSet rs;
%>
...
<%
conn = DriverManager.getConnection( "jdbc://postgresql/www", "user", "pass" );
stat = conn.createStatement();
rs = stat.executeQuery( querySubOU + id );
%>
<jsp:include page="<%= \"page.jsp?partial=true&id=\" + subID %>"/>

But this does work:

<%!
...
%>
<%
Connection conn;
Statement stat;
ResultSet rs;
conn = DriverManager.getConnection( "jdbc://postgresql/www", "user", "pass" );
stat = conn.createStatement();
rs = stat.executeQuery( querySubOU + id );
%>
<jsp:include page="<%= \"page.jsp?partial=true&id=\" + subID %>"/>

Could anyone explain why?

Variables within <%!  %> section are global to the instance of the servlet class or (if declared as "static") global to the whole class. Since I didnot declare them as "static", they should have been used per-instance. Funny thing is, the error was not occuring upon exit from the recursion (as I expected), but upon *second* entering of recursion.

QUESTION
-------------
If a servlet (JSP) tries to include itself, will Tomcat create two instances of the servlet's class? From my point of view, it should, since the caller has not finished.

Can anyone shed some light on the matter?

Nix.