JdbcConnectionPool.java

package dbconn;

import com.mysql.jdbc.Connection;

import java.sql.DriverManager;
import java.sql.SQLException;
import java.util.ArrayList;
import java.util.List;

public class JdbcConnectionPool {

    List<Connection> availableConnections = new ArrayList<>();

    public JdbcConnectionPool()
    {
        initializeConnectionPool();
    }

    private void initializeConnectionPool()
    {
        while(!checkIfConnectionPoolIsFull())
        {
            availableConnections.add(createNewConnectionForPool());
        }
    }

    private synchronized boolean checkIfConnectionPoolIsFull()
    {
        final int MAX_POOL_SIZE = Configuration.getInstance().DB_MAX_CONNECTIONS;

        if(availableConnections.size() < MAX_POOL_SIZE)
        {
            return false;
        }

        return true;
    }

    //Creating a connection
    private Connection createNewConnectionForPool()
    {
        Configuration config = Configuration.getInstance();
        try {
            Class.forName(config.DB_DRIVER);
            Connection connection = (Connection) DriverManager.getConnection(
                    config.DB_URL, config.DB_USER_NAME, config.DB_PASSWORD);
            return connection;
        } catch (ClassNotFoundException e) {
            e.printStackTrace();
        } catch (SQLException e) {
            e.printStackTrace();
        }
        return null;

    }

    public synchronized Connection getConnectionFromPool()
    {
        Connection connection = null;
        if(availableConnections.size() > 0)
        {
            connection = (Connection) availableConnections.get(0);
            availableConnections.remove(0);
        }
        return connection;
    }

    public synchronized void returnConnectionToPool(Connection connection)
    {
        availableConnections.add(connection);
    }
}