Re: [JSP] 2 nested result set

From:
Lew <lew@lewscanon.com>
Newsgroups:
comp.lang.java.programmer
Date:
Fri, 18 Jan 2008 21:41:11 -0500
Message-ID:
<lOydnQXhuY3a_gzanZ2dnUVZ_r-vnZ2d@comcast.com>
Mariano wrote:

I have a JSP file that make an XML Document:


Sidebar: don't put scriptlet in JSPs. See below.

<%@ page contentType="text/xml" pageEncoding="windows-1252"%>
<%@ page language="java" import="java.sql.*"%>
<%
Connection dbconn = null;
Class.forName("com.mysql.jdbc.Driver");
dbconn = DriverManager.getConnection("", "" "");
Statement stmt = dbconn.createStatement();
String query_1;
String query_2;

query_1 = "SELECT * .....";

query_2 = "SELECT * .......";

ResultSet rs1 = stmt.executeQuery(query_1);
ResultSet rs2 = stmt.executeQuery(query_2);


Check out the Javadocs. The answers are so often in the Javadocs, and one
expects that would be the first place one would look.

See below.

%>

<xmlRoot>

<%
    while(rs1.next()) {
    out.println("<son>");


You could emit this tag directly as JSP rather than using scriptlet.

            while (rs2.next()) {
                out.println("<grandchild ...>");
                out.println("</grandchild>");
             }
    out.println("</son>");
    }
%>

</xmlRoot>

root cause


javax.servlet.ServletException: java.sql.SQLException: Operation not
allowed after ResultSet closed

  ...

java.sql.SQLException: Operation not allowed after ResultSet closed
    com.mysql.jdbc.SQLError.createSQLException(SQLError.java:910)
    com.mysql.jdbc.ResultSet.checkClosed(ResultSet.java:666)
    com.mysql.jdbc.ResultSet.next(ResultSet.java:7274)
    ...
Where is the error? As you can see i never close ResultSet, so I don't
understand: Operation not allowed after ResultSet closed


But you do close the first ResultSet:

A ResultSet object is automatically closed when the Statement object that generated it
is closed, re-executed, or used to retrieve the next result from a sequence of multiple results.


This from the Javadocs for ResultSet, the first place you should look for this
problem:
<http://java.sun.com/javase/6/docs/api/java/sql/ResultSet.html>

Sidebar: You can avoid mixing scriptlet in your JSP by using the JSP Standard
Tag Library (JSTL) and the Expression Language.

The JSTL has a rich set of SQL tags that would save you using a DAO layer,
which seems a suitable shortcut for your application.

--
Lew

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