MySQL、oracle分页原生查询

//根据表名 关键字 进行分页查询
 @override
    public jsonarray doget(string tablename, string keyword,int pagenum,int pagesize) {
        resultset result = null;
        preparedstatement pre = null;
        try {
            //根据数据库类型查询表的所有列名
             string datatype = con.getmetadata().getdatabaseproductname();
             string columnsql = "";
             switch (datatype) {
            case "mysql":
                columnsql = "select column_name from information_schema.columns where table_name ='"+tablename+"'";
                break;

            case "oracle":
                columnsql = "select column_name from all_tab_columns where table_name ='"+tablename+"'";
            default:
                break;
            }
             pre = con.preparestatement(columnsql);
             result = pre.executequery();
             //拼接sql
             stringbuilder sql = new stringbuilder("select * from "+tablename+" t where ");
             resultsetmetadata md = result.getmetadata();// 得到结果集(rs)的结构信息，比如字段数、字段名等
             int columncount = md.getcolumncount(); // 返回此 resultset 对象中的列数
             while (result.next()) {
                 for(int i=1;i<=columncount;i++){
                     sql.append(sql.append("t."+result.getobject(i))+" like '%"+keyword+"%' or ");
                 }
            }
            sql = sql.delete(sql.length()-3, sql.length());//去掉sql末尾的or
            if("mysql".equals(datatype)){//mysql分页语句拼接
                sql = sql.append("limit "+pagenum+","+pagesize+"");
            }
            if("oracle".equals(datatype)){//oracle分页语句拼接
                string sqlstr = "select * from (select a.*, rownum rn from ("+sql+") a where rownum <="+pagenum*pagesize+" ) where rn >="+(pagenum-1)*pagesize+"";
                sql = sql.replace(0,sql.length(), sqlstr);
            }
            pre = con.preparestatement(sql.tostring());
            result = pre.executequery();
        } catch (exception e) {
            e.printstacktrace();
        }
        return resultsettolist(pre, result);
    }


/**
     * 将resultset结果集转成jsonarray
     * 
     * @param pre
     * @param rs
     * @return
     * @author 
     */
    public jsonarray resultsettolist(preparedstatement pre, resultset result) {

        if (result == null)
            return null;

        jsonarray array = new jsonarray();
        try {
            resultsetmetadata md = result.getmetadata();// 得到结果集(rs)的结构信息，比如字段数、字段名等

            int columncount = md.getcolumncount(); // 返回此 resultset 对象中的列数

            jsonobject json = null;
            while (result.next()) {
                json = new jsonobject();
                for (int i = 1; i <= columncount; i++) {
                    if(!"".equals(result.getobject(i))){
                        if(result.getobject(i) instanceof date){
                            json.put(md.getcolumnname(i), sdf.format(result.getobject(i)));
                        }else{
                            json.put(md.getcolumnname(i), result.getobject(i));
                        }
                    }else{
                        json.put(md.getcolumnname(i), "");
                    }

                }
                array.put(json);
            }
        } catch (sqlexception | jsonexception e) {
            e.printstacktrace();
        } finally {
            close(result);
            close(pre);
            close(con);
        }

        //"返回json数据：" + array);
        return array;
    }