DatabaseConnection

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package com.mallsystem.server.database;

import java.sql.*;
import java.util.ArrayList;
import com.mallsystem.server.mallsystemserver.Config;
import com.mallsystem.net.packets.data.Row;

/**
 *
 * @author Łukasz
 */
public class DatabaseConnection {
    private static DatabaseConnection dbc;
    private Connection conn;

    private DatabaseConnection() throws SQLException
    {
        conn = DriverManager.getConnection(
                    "jdbc:oracle:thin:@" + Config.DB_HOST + ":" + Config.DB_PORT + ":" + Config.DB_SID, Config.DB_USER, Config.DB_PASS);
    }

    public static DatabaseConnection getInstance() throws SQLException
    {
        if (dbc != null)
            return dbc;
        else
            return dbc = new DatabaseConnection();
    }

    public ArrayList resultSetToArrayList(ResultSet rs) throws SQLException
    {
        ResultSetMetaData md = rs.getMetaData();
        int columns = md.getColumnCount();
        ArrayList <Row> list = new ArrayList<>();

        while (rs.next())
        {
            Row row = new Row(columns);

            for(int i=1; i<=columns; ++i)
                row.put(md.getColumnName(i),rs.getObject(i));

            list.add(row);
        }

        return list;
    }

    public ArrayList query(String q) throws SQLException
    {
        ArrayList <Row> list;

        try (Statement st = conn.createStatement()) {
            ResultSet rs = st.executeQuery(q);
            list = resultSetToArrayList(rs);
        }

        return list;
    }

    public void execute(String q) throws SQLException
    {
        try (Statement st = conn.createStatement()) {
            st.executeUpdate(q);
        }
    }

    public void commit() throws SQLException
    {
        conn.commit();
    }

    public void rollback() throws SQLException
    {
        conn.rollback();
    }

    public void close() throws SQLException
    {
        conn.close();
    }
}