Connection pool

[Mathias Nilsson]

Hi ranchers!
I have made a class that implements the ServletContextListener. In this
servlet I make a Connection that I can use in my application. ( I put it in the Context.setAttribute() ).
My problem is that when I use this the Connection will be opened the whole time the application is alive. I want to make a Connection pool soo that I can close the connections after I have used them.
I'm not sure if I have to close them or what's the best approch when coding this. It is just that I've heard of Connection pooling but I don't know how to do it , why it is soo good etc.
I think by using it the way I have coded now that the Connection must finish before it can run a query again. If I have 500 users that want's to connect to the database then I have a big problem.
My question is.
* How do I code a Connection Pool ?
* What is a Connection Pool. ?
I've read that you should use JNDI instead of DriverManager. Is this correct and why?
// Mathias

[Gregg Bolinger]

Most all servlet container/App Servers offer Connection Pooling through jndi. The web site for your app server should have the documentation available. For example, if you are using Tomcat, you can find information here. Once you have that setup you should be good to go. If you have more problems, let us know and we can help.

[Mathias Nilsson]

Thanks!
The problem now is that I use jdk1.3 and the javax.sql isn't included.
I have installed jdk1.4 , changed my JAVA_HOME but it is still not available. I'm using Tomcat4. I keep getting error on javax.sql import
// Mathias

[Gregg Bolinger]

What doesn javax.sql have to do with using Tomcats connection pooling mechanism?

[Mathias Nilsson]

The samples mysQL , tomcat gave was with that.

DataSource ds = (DataSource) context.lookup("jdbc/MySQLDB");

The DataSource object is in the javax.sql package

[Gregg Bolinger]

Could you display your code AND the error message you are recieving when you compile/run it. Also, if doing this from the command line, include the commands you type to compile/run the program.
Thanks.

[Mathias Nilsson]

Here is the code

package se.edgesoft.listeners;
import javax.servlet.ServletContextListener;
import javax.servlet.ServletContextEvent;
import javax.servlet.ServletContext;
import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.SQLException;
import javax.naming.InitialContext;
import javax.sql.DataSource;
public class ConnectionHandler
implements ServletContextListener{

public void contextInitialized( ServletContextEvent e ){ 
ServletContext context = e.getServletContext();
try{
DataSource ds = (DataSource) context.lookup("jdbc/MySQLDB");
Connection connection = ds.getConnection();

}catch( SQLException se ){
System.out.println( se.getMessage() ) ;
}catch( Exception ex ){
System.out.println( ex.getMessage() ) ;
}finally{
// do something
}


}

public void contextDestroyed( ServletContextEvent e ){
ServletContext context = e.getServletContext();

}
}

Here are the errors

D:\Tomcat4.0\webapps\skyltfabriken\WEB-INF\classes>javac se/edgesoft/listeners/C
onnectionHandler.java
se/edgesoft/listeners/ConnectionHandler.java:10: cannot resolve symbol
symbol  : class DataSource
location: package sql
import javax.sql.DataSource;
                 ^
se/edgesoft/listeners/ConnectionHandler.java:20: cannot resolve symbol
symbol  : class DataSource
location: class se.edgesoft.listeners.ConnectionHandler
                        DataSource ds = (DataSource) context.lookup("jdbc/MySQLD
B");
                        ^
se/edgesoft/listeners/ConnectionHandler.java:20: cannot resolve symbol
symbol  : class DataSource
location: class se.edgesoft.listeners.ConnectionHandler
                        DataSource ds = (DataSource) context.lookup("jdbc/MySQLD
B");
                                         ^
se/edgesoft/listeners/ConnectionHandler.java:20: cannot resolve symbol
symbol  : method lookup  (java.lang.String)
location: interface javax.servlet.ServletContext
                        DataSource ds = (DataSource) context.lookup("jdbc/MySQLD
B");
                                                            ^
4 errors
D:\Tomcat4.0\webapps\skyltfabriken\WEB-INF\classes>

[ November 10, 2003: Message edited by: Mathias Nilsson ]