从数据库里取值方法，写出步骤

private void TestDb() {
        String sql = "select * from table where id=101";
        //JBDC直连
        try {
            /**
             Class.forName("org.gjt.mm.mysql.Driver").newInstance();//装载驱动
                         Connection conn=
             java.sql.DriverManager.getConnection("jdbc:mysql://127.0.0.1","root","");
             Statement stmt=conn.createStatement();//创建Statement，用于执行SQL
             ResultSet rs=stmt.executeQuery(sql);//调用executeQuery()取得结果集
                         while(rs.next())
                         {
                String name=rs.getString("name");
                //....
                         }
             **/
            ///从数据源获得连接///假设server.xml//web.xml配置完毕
            Context initCtx = new javax.naming.InitialContext(); //初始化上下文
            Context envCtx = (Context) initCtx.lookup("java:comp/env"); //查找上下文
            DataSource ds = (DataSource) envCtx.lookup("jdbc/bn"); //查找数据源
            Connection conn = ds.getConnection();
            Statement stmt = conn.createStatement();
            ResultSet rs = stmt.executeQuery(sql);
            while (rs.next()) {
                String name = rs.getString("name");
                //....
            }
            conn.close();
            stmt.close();
            rs.close();
        } catch (Exception ex) {
        }

    }