java查询一次性查询几十万，几百万数据解决办法

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java查询一次性查询几十万，几百万数据解决办法

1、先批量查出所有数据，例子中是一万条一批。
2、在查出数据之后把每次的数据按一定规则存入本地文件。
3、获取数据时，通过批次读取，获得大批量数据。此方法参见：http://yijianfengvip.blog.163.com/blog/static/175273432201191354043148/

以下是查询数据库。按批次查询

public static void  getMonthDataList() {
        ResultSet rs = null;
        Statement stat = null;
        Connection conn = null;
        List list = new ArrayList();
        try {
            conn = createConnection();
            if(conn!=null){
                SimpleDateFormat sdf = new SimpleDateFormat("yyyy-MM-dd");
                SimpleDateFormat timesdf = new SimpleDateFormat("yyyy-MM-dd HH:mm:ss");
                String nowDate = sdf.format(new Date());
                Config.lasttimetext = timesdf.format(new Date());
                String lastDate = sdf.format(CreateData.addDaysForDate(new Date(), 30));
                stat = conn.createStatement(ResultSet.TYPE_SCROLL_SENSITIVE,ResultSet.CONCUR_UPDATABLE);
                int lastrow = 0;
                int datanum = 0;
                String countsql = "SELECT count(a.id) FROM trip_special_flight a" +
                " where a.dpt_date >= to_date('"+nowDate+"','yyyy-mm-dd') " +
                "and a.dpt_date <= to_date('"+lastDate+"','yyyy-mm-dd') and rownum>"+lastrow+" order by a.get_time  desc";
                rs = stat.executeQuery(countsql);
                while (rs.next()) {
                    datanum = rs.getInt(1);
                }
                int onerun = 10000;
                int runnum = datanum%onerun==0?(datanum/onerun):(datanum/onerun)+1;
                for(int r =0;r= to_date('"+nowDate+"','yyyy-mm-dd') " +
                    "and a.dpt_date <= to_date('"+lastDate+"','yyyy-mm-dd')  order by rownum  asc) WHERE rn > "+lastrow;
                    stat.setMaxRows(onerun);
                    stat.setFetchSize(1000);
                    rs = stat.executeQuery(sql);
                    String text = "";
                    int i = 1;
                    while (rs.next()) {
                        text += rs.getString(2)+"|"+rs.getString(3)+"|"+rs.getDate(4)+"|"+rs.getString(5)+"|"+rs.getString(6)+"|"+rs.getString(7)+"|"+rs.getString(8)+"||";
                        if(i%1000==0){
                            FileUtil.appendToFile(Config.tempdatafile, text);
                            text = "";
                        }
                        i++;
                    }
                    if(text.length()>10){
                        FileUtil.appendToFile(Config.tempdatafile, text);
                    }
                    lastrow+=onerun;
                }
            }
        } catch (Exception e) {
            e.printStackTrace();
        } finally {
            closeAll(rs, stat, conn);
        }
    }

转载于:https://my.oschina.net/xiahuawuyu/blog/82588