程序短而简单,稍微可以说一下的是如果一行行写要三四分钟,采用了一次写十万行共写十万次的方式是提高效率的关键。
代码:
import java.io.BufferedWriter; import java.io.IOException; import java.io.PrintWriter; import java.nio.charset.Charset; import java.nio.file.Files; import java.nio.file.Path; import java.nio.file.Paths; import java.nio.file.StandardOpenOption; public class BigFileProducer { public static void main(String[] args) { long startMs=System.currentTimeMillis(); Path filepath=Paths.get("c:\temp\20200229.txt"); Charset u8set=Charset.forName("utf-8"); try(BufferedWriter shadowWriter=Files.newBufferedWriter(filepath, u8set,StandardOpenOption.CREATE)){ PrintWriter writer=new PrintWriter(shadowWriter); for(int i=0;i<10000;i++) { // 运行一万次 System.out.println("#"+i); writer.print(getTenThoasandNums()); // 每次十万行 } }catch(IOException ex) { ex.printStackTrace(); } long endMs=System.currentTimeMillis(); System.out.println("File:'"+filepath+"' created,time elapsed:"+ms2DHMS(startMs,endMs)); } private static String getTenThoasandNums() { StringBuilder sb=new StringBuilder(); for(int i=0;i<100000;i++) { sb.append(rnd(0,100)+" "); } return sb.toString(); } /** * get a random integer between min and max * @param min * @param max * @return */ private static int rnd(int min,int max) { return (int)(min+Math.random()*(max-min+1)); } /** * change seconds to DayHourMinuteSecond format * * @param startMs * @param endMs * @return */ private static String ms2DHMS(long startMs, long endMs) { String retval = null; long secondCount = (endMs - startMs) / 1000; String ms = (endMs - startMs) % 1000 + "ms"; long days = secondCount / (60 * 60 * 24); long hours = (secondCount % (60 * 60 * 24)) / (60 * 60); long minutes = (secondCount % (60 * 60)) / 60; long seconds = secondCount % 60; if (days > 0) { retval = days + "d" + hours + "h" + minutes + "m" + seconds + "s"; } else if (hours > 0) { retval = hours + "h" + minutes + "m" + seconds + "s"; } else if (minutes > 0) { retval = minutes + "m" + seconds + "s"; } else if(seconds > 0) { retval = seconds + "s"; }else { return ms; } return retval + ms; } }
输出:
#9997 #9998 #9999 File:'c: emp20200229.txt' created,time elapsed:1m31s369ms
生成文本文件片段:
52 87 44 62 99 33 53 50 32 58 13 62 84 52 4 95 57 34 40 33 76 38 73 19 86 63 35 5 30 25 37 75 58 59 34 48 82 96 21 76 7 6 97 24 12 69 84 92 22 35 46 68 67 87 62 45 77 84
--2020年2月29日--