转:JDBC连接MYSQL数据库 单例模式

public class SqlHelper
{
    private final Lock lock = new ReentrantLock();
    private static final SqlHelper sqlHelper = new SqlHelper();
    /**
     * 私有的默认构造方法
     */
    private SqlHelper()
    {
    }
    /**
     * 静态方法获得单例
     */
    public static SqlHelper getInstance()
    {
        return sqlHelper;
    }
    private static final String DRIVER = "com.mysql.jdbc.Driver";
    private static final String URL = "jdbc:mysql://localhost:3306/test";
    private static final String USER = "root";
    private static final String PWD = "root";
    private Connection conn = null;
    public Connection getConnection()
    {
        try
        {
            Class.forName(DRIVER);
            return DriverManager.getConnection(URL, USER, PWD);
        } catch (ClassNotFoundException e)
        {
            e.printStackTrace();
        } catch (SQLException e)
        {
            e.printStackTrace();
        }
        return null;
    }
    public ResultSet executeQuery(String sql, Object[] params)
    {
        try
        {
            this.conn = this.getConnection();
            PreparedStatement pst = conn.prepareStatement(sql);
            for (int i = 0; i < params.length; i++)
            {
                pst.setObject(i + 1, params[i]);
            }
            return pst.executeQuery();
        } catch (SQLException e)
        {
            e.printStackTrace();
        }
        return null;
    }
    public void closeConnection()
    {
        try
        {
            if (this.conn != null && !conn.isClosed())
            {
                conn.close();
            }
        } catch (SQLException e)
        {
            e.printStackTrace();
        }
    }
    public ResultSet executeQuery(String sql)
    {
        try
        {
            this.conn = this.getConnection();
            PreparedStatement pst = conn.prepareStatement(sql);
            return pst.executeQuery();
        } catch (SQLException e)
        {
            e.printStackTrace();
        }
        return null;
    }
    public int executeUpdate(String sql, Object[] params)
    {
        this.lock.lock();
        PreparedStatement pst = null;
        int num = 0;
        try
        {
            this.conn = this.getConnection();
            pst = conn.prepareStatement(sql);
            for (int i = 0; i < params.length; i++)
            {
                pst.setObject(i + 1, params[i]);
            }
            num = pst.executeUpdate();
        } catch (SQLException e)
        {
            e.printStackTrace();
        } finally
        {
            this.closeConnection();
            this.lock.unlock();
        }
        return num;
    }
}