工具类JdbcUtils

/* *  * 这是一个工具类，一般工具类不能被继承，所以定义成final *  * 不需要构造实例，用私有的构造方法 *  单例模式或者用static静态代码块， *  本例用static，没有实例 * */package cn.itcast.jdbc;import java.sql.Connection;import java.sql.DriverManager;import java.sql.ResultSet;import java.sql.SQLException;import java.sql.Statement;public final class JdbcUtils {    private static String url = "jdbc:mysql://localhost:3306/jdbc";    private static String user = "root";    private static String password = "123456";    private JdbcUtils() {    }    // 注册驱动    static {        try {            Class.forName("com.mysql.jdbc.Driver");        } catch (Exception e) {            throw new ExceptionInInitializerError(e);        }    }    //建立连接    public static Connection getConnection() throws SQLException {        return DriverManager.getConnection(url, user, password);    }    //释放资源    public static void free(ResultSet rs, Statement st, Connection conn) {        try {            if (rs != null)                rs.close();        } catch (SQLException e) {            e.printStackTrace();        } finally {            try {                if (st != null)                    st.close();            } catch (SQLException e) {                e.printStackTrace();            } finally {                try {                    if (conn != null)                        conn.close();                } catch (SQLException e) {                    e.printStackTrace();                }            }        }    }}