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 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

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。