文件复制 4种方法用时比较

public class FileUtils {
    /**
     * 遍历目录  遍历出目录下的文件名和子目录名
     *
     * @param dir 目录
     * @throws IllegalAccessException
     */
    public static void listDirectory(File dir) throws IllegalAccessException {
        if (!dir.exists()) {
            throw new IllegalAccessException("目录：" + dir + "不存在");
        }
        if (!dir.isDirectory()) {
            throw new IllegalAccessException(dir + "不是目录");
        }
        String[] fileNames = dir.list();
        for (String s : fileNames) {
            System.out.println(dir + "//" + s);
        }
    }

    /**
     * 一个字节一个字节的复制文件
     *
     * @param srcFile
     * @param destFile
     * @throws IllegalAccessException
     * @throws IOException
     */
    public static void copyFileByByte(File srcFile, File destFile) throws IllegalAccessException, IOException {
        if (!srcFile.exists()) {
            throw new IllegalAccessException("文件:" + srcFile + "不存在");
        }
        if (!srcFile.isFile()) {
            throw new IllegalAccessException(srcFile + "不是文件");
        }
        FileInputStream in = new FileInputStream(srcFile);
        FileOutputStream out = new FileOutputStream(destFile);
        int b;
        while ((b = in.read()) != -1) {
            out.write(b);
            out.flush();
        }
        in.close();
        out.close();
    }

    /**
     * 批量复制文件
     *
     * @param srcFile  源文件对象
     * @param destFile 复制到的文件对象
     * @throws IllegalAccessException
     * @throws FileNotFoundException
     */
    public static void copyFile(File srcFile, File destFile) throws IllegalAccessException, IOException {
        if (!srcFile.exists()) {
            throw new IllegalAccessException("文件:" + srcFile + "不存在");
        }
        if (!srcFile.isFile()) {
            throw new IllegalAccessException(srcFile + "不是文件");
        }
        FileInputStream in = new FileInputStream(srcFile);
        FileOutputStream out = new FileOutputStream(destFile);
        byte[] buf = new byte[8 * 1024];
        int b;
        while ((b = in.read(buf, 0, buf.length)) != -1) {
            out.write(buf, 0, b);
            out.flush();
        }
        in.close();
        out.close();
    }

    /**
     * 复制文件 利用缓冲区
     *
     * @param srcFile
     * @param destFile
     * @throws IllegalAccessException
     * @throws IOException
     */
    public static void copyFileByBuffer(File srcFile, File destFile) throws IllegalAccessException, IOException {
        if (!srcFile.exists()) {
            throw new IllegalAccessException("文件:" + srcFile + "不存在");
        }
        if (!srcFile.isFile()) {
            throw new IllegalAccessException(srcFile + "不是文件");
        }
        BufferedInputStream bis = new BufferedInputStream(new FileInputStream(srcFile));
        BufferedOutputStream bos = new BufferedOutputStream(new FileOutputStream(destFile));
        int c = 0;
        while ((c = bis.read()) != -1) {
            bos.write(c);
            //刷新缓存区
            bos.flush();
        }
        bis.close();
        bos.close();
    }

    /**
     * 批量缓存复制文件
     *
     * @param srcFile
     * @param destFile
     * @throws IllegalAccessException
     * @throws IOException
     */
    public static void copyFileBatchBuffer(File srcFile, File destFile) throws IllegalAccessException, IOException {
        if (!srcFile.exists()) {
            throw new IllegalAccessException("文件:" + srcFile + "不存在");
        }
        if (!srcFile.isFile()) {
            throw new IllegalAccessException(srcFile + "不是文件");
        }
        BufferedInputStream bis = new BufferedInputStream(new FileInputStream(srcFile));
        BufferedOutputStream bos = new BufferedOutputStream(new FileOutputStream(destFile));
        byte[] buf = new byte[8 * 1024];
        int b;
        while ((b = bis.read(buf, 0, buf.length)) != -1) {
            bos.write(buf, 0, b);
            bos.flush();
        }
        bis.close();
        bos.close();
    }

    /**
     * 复制 1.76M MP4文件用时比较
     *
     * @param args
     * @throws IllegalAccessException
     * @throws IOException
     */
    public static void main(String[] args) throws IllegalAccessException, IOException {
        long startTime = System.currentTimeMillis();
        //单字节复制用时：6596ms
        copyFileByByte(new File("D:\文件\QQ视频20180718111001.mp4"), new File("D:\文件\1.mp4"));
        //批量复制：6ms
        copyFile(new File("D:\文件\QQ视频20180718111001.mp4"), new File("D:\文件\2.mp4"));
        //单字节缓存复制用时：2709ms
        copyFileByBuffer(new File("D:\文件\QQ视频20180718111001.mp4"), new File("D:\文件\3.mp4"));
        //批量缓存复制用时：5ms
        copyFileBatchBuffer(new File("D:\文件\QQ视频20180718111001.mp4"), new File("D:\文件\4.mp4"));
        long endTime = System.currentTimeMillis();
        System.out.println(endTime - startTime);
    }
}