java JDBC 连接数据库查询数据与直接使用sql的疑问

JDBC 封装衔接是好的条件：
            SystemAuthorizingRealm c = new SystemAuthorizingRealm();
            conn =  c.getConnection();
//          conn = ((DataSource) SpringContextUtil.getBean("dataSource")).getConnection();
            PreparedStatement ps = conn.prepareStatement(sql);
            ps.setString(i1, token.getUsername().trim());
            ps.setString(i2, Encrypt.getMD5(String.valueOf(token.getPassword())).trim());
            System.out.println(Encrypt.getMD5(String.valueOf(token.getPassword())));   

         JDBC 封装衔接是好的条件：
            SystemAuthorizingRealm