HELP!! servlet stops working sometimes!!!

Question

Can somebody please tell me what is wrong with the following code. Im starting to think it might be my sql statements. The servlet works correctly, but every couple days, when I run the servlet, it displays a blank page, and i have to upload the class file to the server again, then the servlet works. This is happening to a couple of my servlets, and I posted the problem on here several times, and each time I thought the problem was fixed, but it is not.
import java.io.*;
import java.sql.*;
import javax.servlet.*;
import javax.servlet.http.*;
public class byTown extends HttpServlet
Connection con = null;
Connection con2 = null;
public void init (ServletConfig cfg)
throws ServletException {
super.init (cfg);
try {
Class.forName("org.gjt.mm.mysql.Driver");
// Get Connection
con = DriverManager.getConnection ("jdbc:mysql://localhost/comperry_main","myusername","mypassword");
con2 = DriverManager.getConnection ("jdbc:mysql://localhost/comperry_main","myusername","mypassword");
}catch(ClassNotFoundException E) {E.printStackTrace();}
catch(SQLException e) {e.printStackTrace();}
public void doGet (HttpServletRequest request,
HttpServletResponse response)
throws ServletException, IOException {
response.setContentType("text/html");
// Have browser ignore cache - force reload
// response.setHeader ("Expires",
// "Mon, 01 Jan 1990 00:00:00 GMT");
Statement stmt = null;
ResultSet result = null;
Statement stmt2 = null;
ResultSet result2 = null;
outline c=new outline();
try {
// Submit query
stmt = con.createStatement();
stmt2 = con2.createStatement();
result = stmt.executeQuery ("SELECT town,phnumber from towns where 1");
// Create output
PrintWriter out = response.getWriter();
out.print(c.header());
while(result.next()) {
result2 = stmt2.executeQuery ("SELECT COUNT(*) as mycount from business_info where (duplicateLink=-1 or duplicateyn=1) and (phone LIKE '%"+result.getString("phnumber")+"%' or Address1 Like '%"+result.getString("town")+"%' or Address2 Like '%"+result.getString("town")+"%') order by 'name'");
result2.next();
out.println("<a href=\"/servlet/myTown?ph="+result.getString("phnumber")+"\">"+result.getString("town")+" ("+result2.getInt("mycount")+" listings)</a><br>");
result2.close();
result.close();
out.print(c.footer());
out.flush();
out.close();
}catch(SQLException e){}
finally {   
try{
if(result!=null)result.close();
if(stmt!=null)stmt.close();
if(result2!=null)result2.close();
if(stmt2!=null)stmt2.close();
}catch(SQLException e){e.printStackTrace();}
public void destroy() {
super.destroy();
try{
con.close();
con2.close();
}catch(SQLException e){e.printStackTrace();}

Answer 1

hai,
JDBC Socket Connection is very costly, because of which everybody use a concept of Pooling the Connection.
The Instantiation of connection object itself takes more time and you never do that kind of coding like.
Go to Google Type "Connection Pool" and download a simpler ConnectionPool Source code and use it.
Or otherwise use the connection pool facility, if your server supports(The actual Impl/specifications are provided by sun , which is nothing but javax.sql.* packages), and I hope almost all javawebservers has a support to connectionPool, which are implmented according to Suns Specification( which would be the best,if u do).
If you use the above code, You will definitely suffer in future.
You should never close the connection, if you have written of your own connection pool (at any cost you should close result and statments).
but if you are using built-in Servers ConnectionPool , then close() method on DataSource Object is more like returning connection to the pool back, rather closing the connection.
You must make sure , that you are returning connections to the pool once after it is used(Normally , should be handled at finally blocks).
(Make sure, your databse supports auto commit facility, if so , do commit and rollback properly without fail, if you had set the autocomit to "false")
If you don't have any idea about Pooling, Please read on some good books
I recommend you, even almost all Collections classes should be pooled , since they are very costly and the instantiation time is more.
With Regards
Lokesh T.C