java 读取txt,java读取大文件

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");

    }

}

来源博客http://yijianfengvip.blog.163.com/blog/static/175273432201191354043148/

java读取 500M 以上文件,java读取大文件