java一次性查询几十万，几百万数据解决办法

java查询一次性查询几十万，几百万数据解决办法

很早的时候写工具用的一个办法。

当时是用来把百万数据打包成rar文件。

所以用了个笨办法。希望高手指导一下，有什么好方法没有啊

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<DataBean> list = new ArrayList<DataBean>();
        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<runnum;r++){
                    System.out.println("getMonthDataList--"+datanum+" 开始查询第"+(r+1)+"批数据");
                    String sql = "SELECT * FROM  (SELECT rownum rn, a.dpt_code, a.arr_code,a.dpt_date,a.airways,a.flight," +
                    "a.cabin,a.price 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')  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);
        }

    }

-----java一次性查询几十万，几百万数据解决办法

存入临时文件之后，再用读取大量数据文件方法。

设置缓存大小BUFFER_SIZE，Config.tempdatafile是文件地址

来源博客

http://yijianfengvip.blog.163.com/blog/static/175273432201191354043148/

package com.yjf.util;
import java.io.File;
import java.io.RandomAccessFile;
import java.nio.MappedByteBuffer;
import java.nio.channels.FileChannel;

public class Test {
    public static void main(String[] args) throws Exception {
        final int BUFFER_SIZE = 0x300000; // 缓冲区为3M
        File f = new File(Config.tempdatafile);
 //  来源博客http://yijianfengvip.blog.163.com/blog/static/175273432201191354043148/
        int len = 0;
        Long start = System.currentTimeMillis();
        for (int z = 8; z >0; z--) {
            MappedByteBuffer inputBuffer = new RandomAccessFile(f, "r")
                    .getChannel().map(FileChannel.MapMode.READ_ONLY,
                            f.length() * (z-1) / 8, f.length() * 1 / 8);
            byte[] dst = new byte[BUFFER_SIZE];// 每次读出3M的内容
            for (int offset = 0; offset < inputBuffer.capacity(); offset += BUFFER_SIZE) {
                if (inputBuffer.capacity() - offset >= BUFFER_SIZE) {
                    for (int i = 0; i < BUFFER_SIZE; i++)
                        dst[i] = inputBuffer.get(offset + i);
                } else {
                    for (int i = 0; i < inputBuffer.capacity() - offset; i++)
                        dst[i] = inputBuffer.get(offset + i);
                }
                int length = (inputBuffer.capacity() % BUFFER_SIZE == 0) ? BUFFER_SIZE
                        : inputBuffer.capacity() % BUFFER_SIZE;
                len += new String(dst, 0, length).length();
                System.out.println(new String(dst, 0, length).length()+"-"+(z-1)+"-"+(8-z+1));
            }
        }
        System.out.println(len);
        long end = System.currentTimeMillis();
        System.out.println("读取文件文件花费：" + (end - start) + "毫秒");
    }

}

读取大量数据文件方法。

原文：http://blog.csdn.net/yjflinchong/article/details/7287648