package com.learnjava.io.nio;

import java.io.FileInputStream;

import java.io.FileOutputStream;

import java.io.IOException;

import java.io.RandomAccessFile;

import java.nio.MappedByteBuffer;

import java.nio.channels.FileChannel;

MappedByteBuffer mappedByteBuffer = channel.map(FileChannel.MapMode.READ_WRITE, 0, 5);

mappedByteBuffer.put(0, (byte)'H');

mappedByteBuffer.put(3, (byte)'9');

mappedByteBuffer.put(0, (byte)'H');

mappedByteBuffer.put(3, (byte)'9');

// IndexOutOfBoundsException

mappedByteBuffer.put(5, (byte)'Y');

mappedByteBuffer.put(5, (byte)'Y');

randomAccessFile.close();

System.out.println("change success");

}

/**

public static void mmap4zeroCopy(String from, String to) throws IOException {

FileChannel source = null;

FileChannel destination = null;

try {

source = new RandomAccessFile(from, "r").getChannel();

destination = new RandomAccessFile(to, "rw").getChannel();

MappedByteBuffer inMappedBuf =

source.map(FileChannel.MapMode.READ_ONLY, 0, source.size());

destination.write(inMappedBuf);

} finally {

if (source != null) {

source.close();

}

if (destination != null) {

destination.close();

}

}

}

public static void sendfile4zeroCopy(String from, String to) throws IOException{

FileChannel source = null;

FileChannel destination = null;

try {

source = new FileInputStream(from).getChannel();

destination = new FileOutputStream(to).getChannel();

source.transferTo(0, source.size(), destination);

} finally {

if (source != null) {

source.close();

}

if (destination != null) {

destination.close();

}

}

}

}

在深入零拷贝机制之前,先来了解下传统BIO通信底层发生了什么,为什么会这么"消耗资源"。Linux服务器是现在绝大多数系统的首选,它的优点就不再赘述,下面的分析都基于Linux环境来进行。作为一台服务器,最常见的功能就是

获取客户端发送过来的请求,然后再去查数据库DB获取到想要的数据,再将数据以一定的业务逻辑处理后传回给客户端,这一过程主要会调用Linux内核的以下两个函数:

在Java程序中,常用的零拷贝有mmap(内存映射)和sendFile。让我们回到IO底层,在Java中,一次IO操作在操作系统底层都做了哪些工作。