JDBCUtils 简单的封装

public class JDBCUtils {

    //增删改
    public static void update (String sql, Object ...args) {//sql中占位符的个数于可变形参的长度相同
        Connection conn = null;
        PreparedStatement ps = null;
        try {
            //1.获取数据库连接
            conn = JDBCUtils.getConnection();
            //2.预编译sql语句，返回PreparedStatement的实例
            ps = conn.prepareStatement(sql);
            //3.填充占位符
            for (int i = 0; i < args.length; i++) {
                ps.setObject(i + 1,args[i]);
            }
            //4.执行
            ps.execute();
        } catch (Exception e) {
            e.printStackTrace();
        }finally {
            //5.关闭资源
            JDBCUtils.closeResourse(conn,ps);
        }
    }

	/**
     * 查询
     * @param clazz
     * @param sql
     * @param args
     * @param <T>
     * @return
     */
    public static <T> List<T> query(Class<T> clazz, String sql, Object ...args) {
        Connection conn = null;
        PreparedStatement ps = null;
        ResultSet rs = null;
        try {
            //1.获取数据库连接
            conn = JDBCUtils.getConnection();
            ps = conn.prepareStatement(sql);
            for (int i = 0; i < args.length; i++) {
                ps.setObject(i+1,args[i]);
            }
            rs = ps.executeQuery();
            //获取结果的元数据：ResultSetMetaData
            ResultSetMetaData rsmd = rs.getMetaData();
            //通过ResultSetMetaData获取结果集中的列数
            int columncount = rsmd.getColumnCount();
            //创建集合对象
            ArrayList<T> list = new ArrayList<T>();
            while (rs.next()){
                T t = clazz.newInstance();
                for (int i = 0; i < columncount; i++) {
                    Object columnValue = rs.getObject(i+1);
                    //获取每个列名
                    String columnName = rsmd.getColumnLabel(i + 1);
                    //利用反射给对象赋值
                    Field field = clazz.getDeclaredField(columnName);
                    field.setAccessible(true);
                    field.set(t,columnValue);
                }
                list.add(t);
            }
            return list;
        } catch (Exception e) {
            e.printStackTrace();
        }finally {
            JDBCUtils.closeResourse(conn,ps,rs);
        }
        return null;
    }
    /**
     * 获取数据库连接
     */
    public static Connection getConnection() throws Exception {
        //1.读取配置文件中的4个基本信息
        InputStream is = ClassLoader.getSystemClassLoader().getResourceAsStream("jdbc.properties");
        Properties pros = new Properties();
        pros.load(is);
        String user = pros.getProperty("user");
        String password = pros.getProperty("password");
        String url = pros.getProperty("url");
        String driverClass = pros.getProperty("driverClass");

        //2.加载驱动
        Class.forName(driverClass);

        //3.获取连接
        Connection conn = DriverManager.getConnection(url, user, password);
        return conn;
    }
    /**
     * 释放资源
     * @param conn
     * @param ps
     */
    public static void closeResourse(Connection conn, Statement ps){
        try {
            if (ps != null){
                ps.close();
            }
        } catch (SQLException throwables) {
            throwables.printStackTrace();
        }
        try {
            if (conn != null){
                conn.close();
            }
        } catch (SQLException throwables) {
            throwables.printStackTrace();
        }
    }
    public static void closeResourse(Connection conn, Statement ps,ResultSet rs){
        try {
            if (ps != null){
                ps.close();
            }
        } catch (SQLException throwables) {
            throwables.printStackTrace();
        }
        try {
            if (conn != null){
                conn.close();
            }
        } catch (SQLException throwables) {
            throwables.printStackTrace();
        }
        try {
            if (rs != null){
                rs.close();
            }
        } catch (SQLException throwables) {
            throwables.printStackTrace();
        }
    }
}