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Java中三种零拷贝的实现示例以及对比详解

目录
  • 简介
  • 传统实现
  • MMAP
  • transferTo
  • 堆外内存
  • 总结

简介

本文主要是介绍几种零拷贝的实现示例,以及与最传统的做一个对比,看看在效率上到底有多大的提升

好了,废话不多说直接干,本章例子是通过网络IO传输一个8M大小的文件,对比传输效率,由于服务端接收端不需要修改,所以我们先上服务端代码:

public static void main(String[] args) throws IOException {
    ServerSocket serverSocket = new ServerSocket(8080);
    System.out.println("服务端:等待连接");
    Socket accept = serverSocket.accept();
    System.out.println("服务端:" + accept.getRemoteSocketAddress() + "已连接");
    File file = new File("C:\\Users\\Administrator编程客栈\\Desktop\\ioTest.txt");
    if(!file.exists()){
        file.createNewFile();
    }
    FileOutputStream fil编程客栈eOutputStream = 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("接收完毕".getBytes());
    accept.shutdownOutput();
    fileOutputStream.close();
    outputStream.close();
    bufferedInputStream.close();
    accept.close();
}

传统实现

正常的socket传输,耗时: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 star编程t = 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("耗时:" + (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("服务端发来消息->" + message);
        inputStream.close();
        outputStream.close();
        socket.close();
    }

MMAP

MMAP原理就是建立了一个文件映射,划分了一个虚拟空间,往这个空间写数据,少了一次拷贝

缺点:空间有限

实践案例:RocketMq

耗时: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("耗时:" + (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("服务端发来消息:" + new String(bytes));
        }
        socketChannel.close();
    }

transferTo

原理就是两个通道之间直接传输数据,根据系统支持程度,少了1-2次拷贝

缺点:局限于文件通道

实践案例:Netty、Kafka

耗时: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("耗时:" + (Sy编程客栈stem.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("服务端发来消息:" + n编程客栈ew String(bytes));
        }
        socketChannel.close();
    }

堆外内存

原理直接使用堆外内存,少了一次拷贝

缺点:堆外内存开启耗时,此内存不受JVM控制,如垃圾回收等

实践案例:Netty

耗时: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("耗时:" + (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("服务端发来消息:" + new String(bytes));
        }
        socketChannel.close();
    }

总结

耗时统计不完全准确,都是多次取平均,具体使用哪种需要看场景来

到此这篇关于Java中三种零拷贝的实现示例以及对比详解的文章就介绍到这了,更多相关Java零拷贝方式对比内容请搜索编程客栈(www.devze.com)以前的文章或继续浏览下面的相关文章希望大家以后多多支持编程客栈(www.devze.com)!

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