// ByteBuffer读取大文件
public static void useFileChannel() {
    try{
        FileInputStream fis = new FileInputStream("你电脑上已经存在的文件路径，例如C:\\file1");
        FileChannel channel = fis.getChannel();
        long start = System.currentTimeMillis();
        ByteBuffer buff = ByteBuffer.allocate((int) channel.size());
        buff.clear();
        channel.read(buff);
        long end = System.currentTimeMillis();
        System.out.println(end - start);
        fis.close();
        channel.close();
    } catch (IOException e) {
        e.printStackTrace();
    }
}

// MappedByteBuffer读取大文件
public static void useMappedByteBuffer() {
    try{
        FileInputStream fis = new FileInputStream("你电脑上已经存在的文件路径，例如C:\\file1");
        FileChannel channel = fis.getChannel();
        long start = System.currentTimeMillis();
        MappedByteBuffer mbb = channel.map(FileChannel.MapMode.READ_ONLY, 0, channel.size());
        long end = System.currentTimeMillis();
        System.out.println(end - start);
        fis.close();
        channel.close();
    } catch (IOException e) {
        e.printStackTrace();
    }
}

public static void main(String[] args) {
    useFileChannel();
    useMappedByteBuffer();
}