java - 下载文件太慢了

Question

我用 Opera 浏览器和 Java 代码尝试了相同的文件。

Opera 浏览器的速度接近 2 MB/s，但 Java 代码的速度不超过 400 KB/s。我的代码有什么问题吗？

我想我用 BufferedReader 阅读时做错了，但我不知道为什么会发生这种情况以及如何修复。

PS:我只是进行速度测试，而不是运行文件。我知道它是一个二进制文件，这对速度有什么影响吗？

            StringBuilder builder = new StringBuilder();
            HttpURLConnection uri = (HttpURLConnection) new URL("http://speedtest.tele2.net/3MB.zip").openConnection();
            uri.setRequestMethod("GET");
            uri.setConnectTimeout(5000);
            InputStream ent = uri.getInputStream();
            BufferedReader reader = new BufferedReader(new InputStreamReader(ent, "iso-8859-1"), 8);
            while ((line = reader.readLine()) != null) {
                builder.append(line + "\n");
            }

Answer 1

我会使用二进制下载来下载二进制文件，当我运行这个时，我得到

public class DownloadMain {
    public static void main(String[] args) throws IOException {
        HttpURLConnection uri = (HttpURLConnection) new URL("http://speedtest.tele2.net/3MB.zip").openConnection();
        uri.setRequestMethod("GET");
        uri.setConnectTimeout(5000);
        InputStream ent = uri.getInputStream();
        ByteArrayOutputStream baos = new ByteArrayOutputStream();
        byte[] bytes = new byte[8192];
        long start = System.currentTimeMillis();
        for (int len; (len = ent.read(bytes)) > 0; )
            baos.write(bytes, 0, len);
        long time = System.currentTimeMillis() - start;
        System.out.printf("Took %.3f seconds to read %.3f MB of data%n",
                time / 1e3, baos.toByteArray().length / 1e6);
    }
}

打印

Took 0.541 seconds to read 3.146 MB of data

接近 6 MB/s

如果您忽略文件是二进制的事实，只是出于性能比较的目的。

public class DownloadMain {
    public static void main(String[] args) throws IOException {
        HttpURLConnection uri = (HttpURLConnection) new URL("http://speedtest.tele2.net/3MB.zip").openConnection();
        uri.setRequestMethod("GET");
        uri.setConnectTimeout(5000);
        InputStream ent =uri.getInputStream();
        Reader reader = new InputStreamReader(ent, StandardCharsets.ISO_8859_1);
        StringWriter sw = new StringWriter();
        char[] chars = new char[8192];
        long start = System.currentTimeMillis();
        for (int len; (len = reader.read(chars)) > 0; )
            sw.write(chars, 0, len);
        long time = System.currentTimeMillis() - start;
        System.out.printf("Took %.3f seconds to read %.3f MB of data%n",
                time / 1e3, sw.toString().length() / 1e6);
    }
}

打印

Took 0.548 seconds to read 3.146 MB of data

所以它可能会稍微慢一些，或者只是随机变化。

相比之下，使用 StringBuilder 并一次读取一行可能会慢一些，但也不会太慢

Took 0.555 seconds to read 3.146 MB of data