为什么我的流复制过程稳定地降低了性能

Question

在复制大文件期间，此代码的运行速度越来越慢。难道我做错了什么？

    InputStream ms2 = new BufferedInputStream(new FileInputStream("/home/fedd/Videos/homevid.mp4"));
    OutputStream fos2 = new BufferedOutputStream(new FileOutputStream("testfile2.mp4", true));

    try {
        int byt;
        int i = 0;
        long time = System.currentTimeMillis();
        while ((byt = ms2.read()) != -1) {
            fos2.write(byt);
            i++;
            if (i > 100000) {
                i = 0;
                long took = System.currentTimeMillis() - time;
                System.out.println("100000 bytes took " + took + " milliseconds which means " + (100000000 / took) + " bytes per second");
            }
        }
        fos2.close();
        ms2.close();
    } catch (Exception e) {
        throw new RuntimeException(e);
    }

我的Java是：

openjdk 10.0.2 2018-07-17 OpenJDK运行时环境（内部版本10.0.2 + 13-Ubuntu-1ubuntu0.18.04.4）

OpenJDK 64位服务器VM（内部版本10.0.2 + 13-Ubuntu-1ubuntu0.18.04.4，混合模式）

Answer 1

每次比较后，您都需要重置基准“时间”。尝试使用此：

if (i > 100000) {
    i = 0;
    long took = System.currentTimeMillis() - time;
    time = System.currentTimeMillis();
    System.out.println("100000 bytes took " + took + " milliseconds which means " + (100000000 / took) + " bytes per second");
}

Answer 2

由于计算错误，因此性能会下降。对于第二个块，您正在从第二个块的大小（但从两个块的时间开始）计算每秒的字节数。尝试time = System.currentTimeMillis();之后添加long took = ...