nio与io

io包是以字节流(stream)、字符流(reader/writer)来进行文件的同步读写。
nio是以通道（channel）的方式进行一步读取。是JDK4以后提出，从写法或者类库上都比io简洁，但必须依赖于io来创建。
旧io的文件复制：

BufferedReader br = new BufferedReader(new FileReader(new File(path)));
        PrintWriter pw = new PrintWriter(new BufferedWriter(new FileWriter(path + "z")));
        String s;
        while ((s = br.readLine())!=null){
            pw.write(s+"\n");
        }
        br.close();
        pw.close();

nio的文件复制：

FileChannel in = new FileInputStream("../fc.in").getChannel();
            FileChannel out = new FileOutputStream("../fc.out1").getChannel();
//type 1:
//            ByteBuffer buffer = ByteBuffer.allocate(GetChannel.BSIZE);
//            while (in.read(buffer)!=-1){
//                buffer.flip();
//                out.write(buffer);
//                buffer.clear();
//            }

            //type 2:
            in.transferTo(0,in.size(),out);
            //type 3:
            out.transferFrom(in,0,in.size());

nio在读入文件时，需要依靠ByteBuffer来存储读到的字节数组，ByteBuffer.flip()可以开启快速存取模式(将当前位置置0)，每次读取完下一次读取前需要清除缓存ByteBuffer.clear()。
-- 在ByteBuffer中，asCharBuffer()方法会将字节以字符的形式输出。该方法存在弊端：

public class BufferToText {
    public static int BSIZE=1024;
    static String path="../data2.out";
    public static void main(String[] args) throws IOException {
        FileChannel fc = new FileOutputStream(path).getChannel();
        fc.write(ByteBuffer.wrap("wa haha haha    \n".getBytes()));//write sth
        fc.close();
        //Read the file
        fc = new FileInputStream(path).getChannel();
        ByteBuffer buff = ByteBuffer.allocate(BSIZE);
        fc.read(buff);
        buff.flip();
        System.out.println(buff.asCharBuffer());//此处采用JAVA默认的UTF-16BE来转换，会乱码
        buff.rewind();
        String encoding = System.getProperty("file.encoding");//the current java file's encoding.
        //此处不会乱码，因为采用系统默认的编码编写，此处采用系统默认编码解码
        System.out.println("Decoded using"+encoding+":"+ Charset.forName(encoding).decode(buff));
//-------------------------------------------------
        fc = new FileOutputStream(path).getChannel();
        fc.write(ByteBuffer.wrap(("hanhong hui huahua ").getBytes("UTF-16be")));
        fc.close();

        //re-read
        fc = new FileInputStream(path).getChannel();
        buff.clear();
        fc.read(buff);
        buff.flip();

        System.out.println(buff.asCharBuffer());
        //------------------------------------------------

        fc = new FileOutputStream(path).getChannel();
        buff = ByteBuffer.allocate(100);
        buff.asCharBuffer().put("ai xiong xiong    ");
        fc.write(buff);
        fc.close();

        //read and display
        fc = new FileInputStream(path).getChannel();
        buff.clear();
        fc.read(buff);
        buff.flip();
        System.out.println(buff.asCharBuffer());
    }
}