Connection Pool not working

[Yosuf Ibrahim]

Hello again


So, you see I decided to go with the flow and check out that thing called a Connection pool and give it a spin. Thing is, it is not working even though I followed This Tutorial to the letter

Or I hope I have been :|

package database;

import java.io.IOException;
import java.io.InputStream;
import java.sql.Connection;
import java.sql.SQLException;
import java.util.Properties;

import org.apache.commons.dbcp2.BasicDataSource;

public class ConnectionUtil {

   private static BasicDataSource ds = null;

   public synchronized static Connection getConnection() {
       Connection conn = null;

       try {

           if (ds == null) {
               Properties props = new Properties();
               InputStream is = ConnectionUtil.class.getClassLoader().getResourceAsStream("db.properties");
               props.load(is);

               ds = new BasicDataSource();
               ds.setDriverClassName(props.getProperty("MYSQL_DB_DRIVER_CLASS"));
               ds.setUrl(props.getProperty("MYSQL_DB_URL"));
               ds.setUsername(props.getProperty("MYSQL_DB_USERNAME"));
               ds.setPassword(props.getProperty("MYSQL_DB_PASSWORD"));

               ds.setInitialSize(10); // The initial number of connections that
                                       // are created when the pool is started.
               ds.setMaxTotal(20); // The maximum number of active connections
                                       // that can be allocated from this pool
           }
           conn = ds.getConnection();

       } catch (SQLException | IOException e) {
           e.printStackTrace();
       }

       return conn;
   }
}

And here's my stacktrace

java.lang.reflect.InvocationTargetException
	at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
	at sun.reflect.NativeMethodAccessorImpl.invoke(Unknown Source)
	at sun.reflect.DelegatingMethodAccessorImpl.invoke(Unknown Source)
	at java.lang.reflect.Method.invoke(Unknown Source)
	at com.sun.javafx.application.LauncherImpl.launchApplicationWithArgs(LauncherImpl.java:389)
	at com.sun.javafx.application.LauncherImpl.launchApplication(LauncherImpl.java:328)
	at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
	at sun.reflect.NativeMethodAccessorImpl.invoke(Unknown Source)
	at sun.reflect.DelegatingMethodAccessorImpl.invoke(Unknown Source)
	at java.lang.reflect.Method.invoke(Unknown Source)
	at sun.launcher.LauncherHelper$FXHelper.main(Unknown Source)
Caused by: java.lang.NoClassDefFoundError: org/apache/commons/pool2/SwallowedExceptionListener
	at database.ConnectionUtil.getConnection(ConnectionUtil.java:25)
	at application.AccountDaoImpl.getAccounts(AccountDaoImpl.java:25)
	at application.Main.main(Main.java:28)
	... 11 more
Caused by: java.lang.ClassNotFoundException: org.apache.commons.pool2.SwallowedExceptionListener
	at java.net.URLClassLoader.findClass(Unknown Source)
	at java.lang.ClassLoader.loadClass(Unknown Source)
	at sun.misc.Launcher$AppClassLoader.loadClass(Unknown Source)
	at java.lang.ClassLoader.loadClass(Unknown Source)
	... 14 more
Exception running application application.Main

[Paul Clapham]

Does your Maven POM exactly match what's in the tutorial? And when you ran Maven, did it run successfully?

[Yosuf Ibrahim]

Paul Clapham wrote:Does your Maven POM exactly match what's in the tutorial? And when you ran Maven, did it run successfully?

Sorry for teh stupid question, but what is maven??

[Paul Clapham]

It's a widely-used tool which goes out to various internet sites and downloads the software necessary to support things.

The first picture in the tutorial you linked to contains the XML file which Maven would use. I suppose that since the tutorial didn't specifically say to do anything with that, you're justified in ignoring it completely and claiming that you followed the tutorial "to the letter".

I would suggest finding a different tutorial. Learning Maven just so that you can complete this step is, I think, far too much of a diversion.

[Stephan van Hulst]

I agree that it looks like a poor tutorial, but on the other hand I also believe Maven should be standard knowledge for any Java programmer who is at the level of using connection pools.

IF Yosuf Ibrahim doesn't have to rush to finish this task, now is as good a time as any to learn Maven.

[Tim Holloway]

I need to make sure we all know what we're actually talking about here.

When you say "use a Connection Pool", we normally expect that means that you're going to be working with a multi-user system such as a webserver where your actual application will be a Connection Pool client.

But the code sample is what I'd expect to see if you were trying to implement a Connection Pool [bserver.[/b] Which would generally be built as a JAR ibrary to be either plugged into a framework that supports Connection Pools or as part of a stand-alone Pool Client application (which isn't often done).

To be a Connection Pool client as a web application, you don't need any Apache code. You just need the javax.sql.DataSource interface which is part of the J2EE and JEE implementations and a way to locate that DataSource implementation, which is usually via a JNDI lookup. The Connection Pool itself is a plug-in component to the webapp server, and generally one will already have been bundled as part of the webapp server.

If you actually are attempting to define a wholly new Connection Pool librarty we'd need to know more about what it was expected to do that none of the ready-made Connection Pool implementations don't do.

[Paul Clapham]

Stephan van Hulst wrote:I agree that it looks like a poor tutorial, but on the other hand I also believe Maven should be standard knowledge for any Java programmer who is at the level of using connection pools.

IF Yosuf Ibrahim doesn't have to rush to finish this task, now is as good a time as any to learn Maven.

I suppose that's right too. When I installed a connection pool (in March 2019) I chose c3p0, which didn't have any external dependencies and which documented what jar files needed to go in your classpath. So I didn't need Maven, which was fortunate because I've never used it. But when I upgraded my version of Apache POI (in March 2020) there were a lot of external dependencies which I had to track down the hard way, and knowing Maven would have been useful then.

(In other words: you can see my bias regarding Maven.)