Java中三種零拷貝的實現(xiàn)示例以及對比詳解

更新時間：2023年12月21日 10:49:01 作者：Colins~

這篇文章主要介紹了Java中三種零拷貝的實現(xiàn)示例以及對比詳解,本文主要是介紹幾種零拷貝的實現(xiàn)示例,以及與最傳統(tǒng)的做一個對比,看看在效率上到底有多大的提升,需要的朋友可以參考下

簡介

本文主要是介紹幾種零拷貝的實現(xiàn)示例，以及與最傳統(tǒng)的做一個對比，看看在效率上到底有多大的提升

好了，廢話不多說直接干，本章例子是通過網絡IO傳輸一個8M大小的文件，對比傳輸效率，由于服務端接收端不需要修改，所以我們先上服務端代碼：

public static void main(String[] args) throws IOException {
    ServerSocket serverSocket = new ServerSocket(8080);
    System.out.println("服務端：等待連接");
    Socket accept = serverSocket.accept();
    System.out.println("服務端：" + accept.getRemoteSocketAddress() + "已連接");
    File file = new File("C:\\Users\\Administrator\\Desktop\\ioTest.txt");
    if(!file.exists()){
        file.createNewFile();
    }
    FileOutputStream fileOutputStream = new FileOutputStream(file);
    InputStream bufferedInputStream = accept.getInputStream();
    byte[] bytes = new byte[2048];
    int read;
    while ((read = bufferedInputStream.read(bytes,0,2048)) != -1) {
        fileOutputStream.write(bytes);
    }
    OutputStream outputStream = accept.getOutputStream();
    outputStream.write("接收完畢".getBytes());
    accept.shutdownOutput();
    fileOutputStream.close();
    outputStream.close();
    bufferedInputStream.close();
    accept.close();
}

傳統(tǒng)實現(xiàn)

正常的socket傳輸，耗時:46ms

public static void normal() throws IOException {
        Socket socket = new Socket("127.0.0.1", 8080);
        OutputStream outputStream = socket.getOutputStream();
        InputStream inputStream = socket.getInputStream();
        long start = System.currentTimeMillis();
        File file = new File("C:\\Users\\Administrator\\Desktop\\222.txt");
        FileInputStream fileInputStream = new FileInputStream(file);
        byte[] bytes1 = new byte[2048];
        while (fileInputStream.read(bytes1, 0, 2048) != -1) {
            outputStream.write(bytes1);
        }
        socket.shutdownOutput();
        System.out.println("耗時：" + (System.currentTimeMillis() - start));
        byte[] bytes = new byte[1024];
        String message = "";
        int read;
        while ((read = inputStream.read(bytes)) != -1) {
            message += new String(bytes, 0, read);
        }
        System.out.println("服務端發(fā)來消息->" + message);
        inputStream.close();
        outputStream.close();
        socket.close();
    }

MMAP

MMAP原理就是建立了一個文件映射，劃分了一個虛擬空間，往這個空間寫數(shù)據，少了一次拷貝

缺點：空間有限

實踐案例：RocketMq

耗時：32ms

public static void mmp() throws IOException {
        SocketChannel socketChannel = SocketChannel.open();
        socketChannel.connect(new InetSocketAddress("127.0.0.1", 8080));
        long start = System.currentTimeMillis();
        Path path = Paths.get("C:\\Users\\Administrator\\Desktop\\222.txt");
        FileChannel open = FileChannel.open(path, StandardOpenOption.READ);
        MappedByteBuffer map = open.map(FileChannel.MapMode.READ_ONLY, 0, open.size());
        socketChannel.write(map);
        socketChannel.shutdownOutput();
        System.out.println("耗時：" + (System.currentTimeMillis() - start));
        ByteBuffer allocate = ByteBuffer.allocate(1024);
        int read = socketChannel.read(allocate);
        if (read > 0) {
            allocate.flip();
            byte[] bytes = new byte[allocate.remaining()];
            allocate.get(bytes);
            System.out.println("服務端發(fā)來消息：" + new String(bytes));
        }
        socketChannel.close();
    }

transferTo

原理就是兩個通道之間直接傳輸數(shù)據，根據系統(tǒng)支持程度，少了1-2次拷貝

缺點：局限于文件通道

實踐案例：Netty、Kafka

耗時：18ms

 public static void transferTo() throws IOException {
        SocketChannel socketChannel = SocketChannel.open();
        socketChannel.connect(new InetSocketAddress("127.0.0.1", 8080));
        long start = System.currentTimeMillis();
        Path path = Paths.get("C:\\Users\\Administrator\\Desktop\\222.txt");
        FileChannel open = FileChannel.open(path, StandardOpenOption.READ);
        long l = open.transferTo(0, open.size(), socketChannel);
        socketChannel.shutdownOutput();
        System.out.println("耗時：" + (System.currentTimeMillis() - start));
        ByteBuffer allocate = ByteBuffer.allocate(1024);
        int read = socketChannel.read(allocate);
        if (read > 0) {
            allocate.flip();
            byte[] bytes = new byte[allocate.remaining()];
            allocate.get(bytes);
            System.out.println("服務端發(fā)來消息：" + new String(bytes));
        }
        socketChannel.close();
    }

堆外內存

原理直接使用堆外內存，少了一次拷貝

缺點：堆外內存開啟耗時，此內存不受JVM控制，如垃圾回收等

實踐案例：Netty

耗時：26ms

public static void outSide() throws IOException {
        SocketChannel socketChannel = SocketChannel.open();
        socketChannel.connect(new InetSocketAddress("127.0.0.1", 8080));
        long start = System.currentTimeMillis();
        Path path = Paths.get("C:\\Users\\Administrator\\Desktop\\222.txt");
        FileChannel open = FileChannel.open(path, StandardOpenOption.READ);
        ByteBuffer byteBuffer = ByteBuffer.allocateDirect((int) open.size());
        open.read(byteBuffer);
        byteBuffer.flip();
        socketChannel.write(byteBuffer);
        socketChannel.shutdownOutput();
        System.out.println("耗時：" + (System.currentTimeMillis() - start));
        ByteBuffer allocate = ByteBuffer.allocate(1024);
        int read = socketChannel.read(allocate);
        if (read > 0) {
            allocate.flip();
            byte[] bytes = new byte[allocate.remaining()];
            allocate.get(bytes);
            System.out.println("服務端發(fā)來消息：" + new String(bytes));
        }
        socketChannel.close();
    }