Question

以下Java代码以两种方式复制文件哪个更高效？希望能够解释原因，谢谢。顺便说一句，我测试了相同的文件，大小约为300兆字节。第一种方法的速度和第二种方法一样快。但经过多次测试，结果却不同。我的测试结果之一如下：

NO.1：使用transferFrom花了3396ms
NO.1：使用时间为3334ms
NO.2：使用transferFrom花了4239ms
NO.2：使用时间为3225毫秒
NO.3：使用transferFrom花了3906ms
NO.3：使用时间为4153ms
NO.4：使用transferFrom花了3100ms
NO.4：使用时间为3174毫秒
NO.5：使用transferFrom花了3156ms
NO.5：使用时间为3180毫秒

代码：

public void copyData(String inPath, String outPath1, String outPath2) {
    FileChannel inChannel = null;
    FileChannel outChannel = null;
    FileInputStream fin = null;
    FileOutputStream fout = null;
    File out1File = null;
    File out2File = null;
    int bufferLen = 20480 * 2 * 1024;
    long runTime;
    ByteBuffer bb = ByteBuffer.allocateDirect(bufferLen);

    for (int i = 0; i < 5; i++) {
        try {
            fin = new FileInputStream(new File(inPath));
            out1File = new File(outPath1);
            fout = new FileOutputStream(out1File);
            inChannel = fin.getChannel();
            outChannel = fout.getChannel();
            runTime = System.currentTimeMillis();
            outChannel.transferFrom(inChannel, 0, inChannel.size());
            runTime = System.currentTimeMillis() - runTime;
            System.out.println("NO." + (i + 1) + ": "
                    + "Using transferFrom took " + runTime + "ms");

        } catch (FileNotFoundException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        } catch (IOException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        } finally {
            if (null != fin) {
                try {
                    fin.close();
                } catch (IOException e) {
                    // TODO Auto-generated catch block
                    e.printStackTrace();
                }
            }
            if (null != fout) {
                try {
                    fout.close();
                } catch (IOException e) {
                    // TODO Auto-generated catch block
                    e.printStackTrace();
                }
            }
            if (null != inChannel) {
                try {
                    inChannel.close();
                } catch (IOException e) {
                    // TODO Auto-generated catch block
                    e.printStackTrace();
                }
            }
            if (null != outChannel) {
                try {
                    outChannel.close();
                } catch (IOException e) {
                    // TODO Auto-generated catch block
                    e.printStackTrace();
                }
            }
            out1File.deleteOnExit();
        }
        /**********************************************************/
        try {
            fin = new FileInputStream(new File(inPath));
            out2File = new File(outPath2);
            fout = new FileOutputStream(out2File);
            inChannel = fin.getChannel();
            outChannel = fout.getChannel();
            runTime = System.currentTimeMillis();
            while (true) {
                int ret = inChannel.read(bb);
                if (ret == -1) {
                    break;
                }
                bb.flip();
                outChannel.write(bb);
                bb.clear();
            }
            runTime = System.currentTimeMillis() - runTime;
            System.out.println("NO." + (i + 1) + ": " + "Using while took "
                    + runTime + "ms");
        } catch (FileNotFoundException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        } catch (IOException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        } finally {
            if (null != fin) {
                try {
                    fin.close();
                } catch (IOException e) {
                    // TODO Auto-generated catch block
                    e.printStackTrace();
                }
            }
            if (null != fout) {
                try {
                    fout.close();
                } catch (IOException e) {
                    // TODO Auto-generated catch block
                    e.printStackTrace();
                }
            }
            if (null != inChannel) {
                try {
                    inChannel.close();
                } catch (IOException e) {
                    // TODO Auto-generated catch block
                    e.printStackTrace();
                }
            }
            if (null != outChannel) {
                try {
                    outChannel.close();
                } catch (IOException e) {
                    // TODO Auto-generated catch block
                    e.printStackTrace();
                }
            }
            out2File.deleteOnExit();
        }
    }
}

使用FileChannel.transferFrom和while（）时，哪种复制数据在Java中更快？

0 个答案: