Will the performance of my web app decrease if i try this code?

Question

I create "DataSourceConnection" class follow Singleton Pattern, but I want to connect to multi-database, so I write "getDataSource(String driver,String url, String username,String password)" function that will return BasicDataSource variable. I save this variable to ServletContext's attribute, and when I need connect to which database I take it from ServletContext. Should I try to use this solution?

import java.io.Serializable;
import java.sql.Connection;
import java.sql.PreparedStatement;
import java.sql.ResultSet;
import java.sql.SQLException;

import javax.sql.DataSource;

import org.apache.commons.dbcp2.BasicDataSource;

public class DataSourceConnection implements Cloneable, Serializable {

    private static final long serialVersionUID = 1L;

    private BasicDataSource dataSource;

    private static class DataSourceConnectionHolder {
        private static DataSourceConnection INSTANCE = new CustomerDataSourceConnection();
    }

    protected Object clone() throws CloneNotSupportedException {
        return new CloneNotSupportedException();
    }

    private DataSourceConnection() {
    }

    public static DataSourceConnection getInstance() {
        return DataSourceConnectionHolder.INSTANCE;
    }

    public DataSource getDataSource(String driver, String url, String username, String password) {
        dataSource = new BasicDataSource();
        dataSource.setDriverClassName(driver);
        dataSource.setUsername(username);
        dataSource.setPassword(password);
        return dataSource;
    }

    public Connection getConnection() throws SQLException {
        return dataSource.getConnection();
    }
}

I suggest you profile it and see. If you have done this recently there could be any number of things which are much more significant than what you are looking at here. — Peter Lawrey, Aug 18 '15 at 17:23
If you are not measuring, you are guessing. Even experts in code optimisation, often get it wrong when they try to guess which is why the only way is to have some measure to give you a hint. — Peter Lawrey, Aug 18 '15 at 17:26

Andreas · Accepted Answer · 2015-08-18T18:23:59.897

The purpose of the singleton pattern in this context would be to only create a single connection to the database (which is a slow operation), and reuse that connection in your code.

Since you want to connect to multiple databases, you'll need a "singleton" for each database. You shouldn't implement multiple classes for this, just a single class with multiple static "shared" connections.

It is the getConnection() that's slow, unless the DataSource maintains a connection pool.

Updated with example

public final class DataSourceConnection {
    // This defines an instance of the class
    private BasicDataSource dataSource;
    private DataSourceConnection(String driver, String url, String username, String password) {
        this.dataSource = new BasicDataSource();
        this.dataSource.setDriverClassName(driver);
        this.dataSource.setUrl(url);
        this.dataSource.setUsername(username);
        this.dataSource.setPassword(password);
    }
    public Connection getConnection() throws SQLException {
        return this.dataSource.getConnection();
    }
    // This defines the "shared"/"multiple singleton" instances
    public static final DataSourceConnection DATABASE1 = new DataSourceConnection("...", "...", "...", "...");
    public static final DataSourceConnection DATABASE2 = new DataSourceConnection("...", "...", "...", "...");
    public static final DataSourceConnection DATABASE3 = new DataSourceConnection("...", "...", "...", "...");
}

And you would use it like this:

try (Connection conn = DataSourceConnection.DATABASE2.getConnection()) {
    // Access database #2 here
}

Of course, in reality, you'd want the initialization of your 3 Data Sources to be based on some configuration file, not to be hardcoded like shown.

I don't get that when you say:" a single class with multiple static "shared" connections. Can you explain it with code? — Hoang Giang, Aug 18 '15 at 18:12

Will the performance of my web app decrease if i try this code?

1 Answers1