java 读取txt,java读取大文件

Posted 2020-07-14 有梦就能实现

java 读取txt,java读取大文件

package com.bbcmart.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 = 0x1200000;// 缓冲大小为12M
       
        System.out.println(BUFFER_SIZE);

        File f = new File(Config.tempdatafile);
 
        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12M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");
    }
}