Question

我最近读到，在较新的计算机中，由于多核计算机的新可用性，Java的I / O性能优于NIO。

我运行了一个快速测试，使用localhost环回地址比较了LAN上I / O和NIO的传输时间。

注意：这是使用JDK 7

结果（3次试验）：

I / O转移平均 21789.3ms

NIO转移平均 22771.0ms

值得注意的是，与I / O相比，每次NIO传输的CPU使用率似乎都要高出约10％。

我的问题是，如果我的比较代码是公平的吗？我是否写好/等于I / O和NIO代码？如果没有，我该如何改进并重新运行此测试？

    public static void main(String[] args) {
    System.out.println("Initiating test sequence...");
    new Thread(new Client()).start();
    try {
        System.out.println("Server I/O initiating...");
        ServerSocket server = new ServerSocket(5555);
        Socket sock = server.accept();
        System.out.println("Server connected to client successfully");
        InputStream is = sock.getInputStream();
        File output = new File("C:/test_root/video.avi");
        FileOutputStream fos = new FileOutputStream(output);
        byte[] data = new byte[1024];
        int len=0;
        System.out.println("Server initiating transfer - Timer starting");
        long start = System.currentTimeMillis();
        while((len=is.read(data))>0) {
            fos.write(data, 0, len);
            fos.flush();
        }
        fos.close();
        is.close();
        sock.close();
        server.close();
        long end = System.currentTimeMillis();
        System.out.println("Network I/O transfer time = "+(end-start)+"ms");

        System.out.println("Server NIO initiating...");
        ServerSocketChannel serverChan = ServerSocketChannel.open();
        serverChan.bind(new InetSocketAddress(5555));
        SocketChannel chan = serverChan.accept();
        chan.configureBlocking(false);
        System.out.println("Server channel connected");
        FileChannel fc = (FileChannel) Files.newByteChannel(Paths.get("C:/test_root/video.avi"), StandardOpenOption.CREATE, StandardOpenOption.WRITE);
        ByteBuffer buff = ByteBuffer.allocate(1024);
        System.out.println("Server initiating transfer - Timer starting");
        start = System.currentTimeMillis();
        while(chan.read(buff)>=0 || buff.position() > 0) {
            buff.flip();
            fc.write(buff);
            buff.compact();
        }
        chan.close();
        fc.close();
        serverChan.close();
        end = System.currentTimeMillis();
        System.out.println("Network NIO transfer time = "+(end-start)+"ms");
    } catch (IOException e) {
        e.printStackTrace();
    }
    System.out.println("Test completed!");
}

static class Client implements Runnable {

    public void run() {
        try {
            System.out.println("Client I/O initiating...");
            Socket sock = new Socket("localhost", 5555);
            System.out.println("Client connected to server successfully!");
            OutputStream os = sock.getOutputStream();
            File input = new File(System.getProperty("user.home")+"/Documents/clip0025.avi");
            FileInputStream fis = new FileInputStream(input);
            byte[] data = new byte[1024];
            int len=0;
            int tot=0;
            int perc=0;
            while((len=fis.read(data))>0) {
                os.write(data, 0, len);
                os.flush();
                tot+=len;
                int prev = perc;
                perc = getPercentage(tot, input.length());
                if(perc !=prev && (perc == 10 || perc == 25 || perc == 50 || perc == 75 || perc == 98))
                    System.out.println("Client reporting: "+perc+"% read");
            }
            os.close();
            fis.close();
            sock.close();

            try {
                Thread.sleep(2000);
            } catch (InterruptedException e) {
                e.printStackTrace();
            }
            System.out.println("Client NIO initiating...");
            SocketChannel sc = SocketChannel.open();
            boolean connected = sc.connect(new InetSocketAddress("localhost",5555));
            if(!connected)
                connected = sc.finishConnect();
            if(!connected)
                throw(new IOException("Client failed to connect"));
            System.out.println("Client channel connected");
            sc.configureBlocking(false);
            FileChannel fc = (FileChannel) Files.newByteChannel(input.toPath(), StandardOpenOption.READ);
            ByteBuffer buff = ByteBuffer.allocate(1024);
            len=0;
            tot=0;
            while((len=fc.read(buff))>=0||buff.position()>0) {
                buff.flip();
                sc.write(buff);
                buff.compact();
                tot+=len;
                int prev = perc;
                perc = getPercentage(tot, input.length());
                if(perc !=prev && (perc == 10 || perc == 25 || perc == 50 || perc == 75 || perc == 98))
                    System.out.println("Client reporting: "+perc+"% read");
            }
            sc.close();
            fc.close();
        } catch (IOException e) {
            e.printStackTrace();
        }
    }
}

其他信息：

Dell Studio XPS 435MT上的Windows Vista（SP2）

第一代i7四核处理器2.67GHz

6GB RAM

64位架构

Answer 1

建议

尝试将阻止IO与阻止NIO进行比较。你的代码会更短。如果要测试IO，请在客户端和服务器上使用IO。如果您打算使用NIO，请在两端使用相同的内容。
使用直接ByteBuffers。
不要读取/写入文件，因为它们不是基准测试的一部分，而且速度要慢得多。只需传递空白数据块。
尝试不同的块大小，例如8 KB。
考虑您要交换的数据类型。例如ByteBuffer可以提高阅读int和long的效率。
以带宽报告数字。我希望看到在循环回来的1-3 GB /秒之间。

http://vanillajava.blogspot.com/2010/07/java-nio-is-faster-than-java-io-for.html

Java I / O与NIO：快速基准比较

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