Singleton java

singleton.java

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package com.shoppingcar.model.dao.postgres;

import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.PreparedStatement;
import java.sql.ResultSet;
import java.sql.SQLException;

/**
 *
 * @author Thom
 */
public class PSQLConnection {

    private static PSQLConnection instance;
    private final String url = "";
    private final String username = "";
    private final String password = "";
    private Connection cn;

    private PSQLConnection() throws SQLException {
        try {
            Class.forName("org.postgresql.Driver");
            this.cn = DriverManager.getConnection(url, username, password);
        } catch (ClassNotFoundException ex) {
            System.out.println("Error connection "+ex);
        }
    }

    public synchronized static PSQLConnection getConnection() throws SQLException {
        if (instance == null || instance.getCon().isClosed()) {
            instance = new PSQLConnection();
        }
        return instance;
    }

    public static void closeConnection(ResultSet res, PreparedStatement prep) {
        try {
            if (instance != null){
                instance.getCon().close();
                instance=null;
            }
            if (res != null) res.close();
            if (prep != null) prep.close();
            
        } catch (SQLException ex) {
            System.out.println("Error close connection "+ex);
        }
    }
    private Connection getCon(){
        return cn;
    }
}