Operation not allowed after ResultSet closed

<%@ page language="java" contentType="text/html; charset=gbk"
    pageEncoding="gbk"%>
<%@ page import="java.sql.*" %><%!
String str="";
private void tree(Connection conn,int id,int level){
Statement stmt = null;
ResultSet rs = null;
String preStr ="";
for(int i=0;i<level;i++){
preStr +="----";
}
try{
stmt  = conn.createStatement();
String sql = "select * from article where pid =" +id;
rs = stmt.executeQuery(sql);
while(rs.next()){
str += "<tr><td>"+rs.getInt("id")+"</td><td>"+
preStr +"<a href='detail.jsp?id=" + rs.getInt("id")+"'>"+rs.getString("title")+"</a>"+
"<a href='delete.jsp?id=" +rs.getInt("id") +"&pid="+rs.getInt("pid")+"'>删除</a>"+
"</td></tr>";
if(rs.getInt("isLeaf")!=0){
tree(conn,rs.getInt("id"),level+1);
}
}
}catch(SQLException e){
e.printStackTrace();
}finally{
try{
if(rs !=null){
rs.close();
rs = null;
}
if(stmt !=null){
stmt.close();
stmt = null;
}
if(conn != null){
conn.close();
conn = null;
}
}catch(SQLException e){
e.printStackTrace();
}
}
}%><%
Class.forName("com.mysql.jdbc.Driver");
String url = "jdbc:mysql://localhost:3306/bbs2?user=root&password=12345";
Connection conn = DriverManager.getConnection(url);  

Statement stmt = conn.createStatement();
ResultSet rs = stmt.executeQuery("select * from article where pid=0");

while(rs.next()){
str +="<tr><td>"+rs.getInt("id")+"</td><td>"+
"<a href='detail.jsp?id=" + rs.getInt("id")+ "'>"+rs.getString("title") + "</a></td><td>" + 
"<a href='delete.jsp?id=" +rs.getInt("id") + "&pid="+ rs.getInt("pid")+"'>删除 </a>"+
"</td></tr>";

if(rs.getInt("isLeaf") != 0){
tree(conn,rs.getInt("id"),1);
}
}
rs.close();
stmt.close();
conn.close();
%>
    
<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=gbk">
<title>Insert title here</title>
</head>
<body>
<table border="1">
<%= str %>
<%str=""; %></table>HTTP Status 500 - --------------------------------------------------------------------------------type Exception reportmessage description The server encountered an internal error () that prevented it from fulfilling this request.exception javax.servlet.ServletException: Operation not allowed after ResultSet closed
org.apache.jasper.runtime.PageContextImpl.doHandlePageException(PageContextImpl.java:825)
org.apache.jasper.runtime.PageContextImpl.handlePageException(PageContextImpl.java:758)
org.apache.jsp.article_jsp._jspService(article_jsp.java:146)
org.apache.jasper.runtime.HttpJspBase.service(HttpJspBase.java:94)
javax.servlet.http.HttpServlet.service(HttpServlet.java:802)
org.apache.jasper.servlet.JspServletWrapper.service(JspServletWrapper.java:324)
org.apache.jasper.servlet.JspServlet.serviceJspFile(JspServlet.java:292)
org.apache.jasper.servlet.JspServlet.service(JspServlet.java:236)
javax.servlet.http.HttpServlet.service(HttpServlet.java:802)
root cause java.sql.SQLException: Operation not allowed after ResultSet closed
com.mysql.jdbc.SQLError.createSQLException(SQLError.java:1073)
com.mysql.jdbc.SQLError.createSQLException(SQLError.java:987)
com.mysql.jdbc.SQLError.createSQLException(SQLError.java:982)
com.mysql.jdbc.SQLError.createSQLException(SQLError.java:927)
com.mysql.jdbc.ResultSetImpl.checkClosed(ResultSetImpl.java:794)
com.mysql.jdbc.ResultSetImpl.next(ResultSetImpl.java:7145)
org.apache.jsp.article_jsp._jspService(article_jsp.java:103)
org.apache.jasper.runtime.HttpJspBase.service(HttpJspBase.java:94)
javax.servlet.http.HttpServlet.service(HttpServlet.java:802)
org.apache.jasper.servlet.JspServletWrapper.service(JspServletWrapper.java:324)
org.apache.jasper.servlet.JspServlet.serviceJspFile(JspServlet.java:292)
org.apache.jasper.servlet.JspServlet.service(JspServlet.java:236)
javax.servlet.http.HttpServlet.service(HttpServlet.java:802)
note The full stack trace of the root cause is available in the Apache Tomcat/5.0.28 logs.
--------------------------------------------------------------------------------Apache Tomcat/5.0.28
</body></html>
没找到错误啊