java 讀取txt,java讀取大文件

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;// 緩沖大小為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];// 每次讀出12M的內容
??????????? 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("讀取文件文件花費：" + (end - start) + "毫秒");
??? }
}

轉載于:https://www.cnblogs.com/firstdream/p/5535990.html

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