# NIO

传统IO基于字节流或字符流进行文件读写，以及使用Socket和ServerSocket进行网络传输。

NIO使用通道（Channel）和缓冲区（Buffer）进行文件操作，以及使用SocketChannel和ServerSocketChannel进行网络传输。

传统IO采用阻塞式模型，对于每个连接，都需要创建一个独立的线程来处理读写操作，而在读写的这个过程中是无法执行其他任务。这会导致大量县城的创建和销毁，以及上下文切换，降低了系统性能。

NIO使用非阻塞模型，允许线程在IO执行时执行其他任务。这种模式通过使用选择器（Selector）来监控多个通道（Channel）上的IO事件，实现了更高的性能和可伸缩性。

JDK1.4中，java.nio.\*包中引入新的I/O库，其目的是提高速度。实际上旧的IO包已经使用NIO重新实现过。

```java
 // 使用传统的 I/O 方法传输文件
    private long transferFile(File source, File des) throws IOException {
        long startTime = System.currentTimeMillis();

        if (!des.exists())
            des.createNewFile();

        // 创建输入输出流
        BufferedInputStream bis = new BufferedInputStream(new FileInputStream(source));
        BufferedOutputStream bos = new BufferedOutputStream(new FileOutputStream(des));

        // 使用数组传输数据
        byte[] bytes = new byte[1024 * 1024];
        int len;
        while ((len = bis.read(bytes)) != -1) {
            bos.write(bytes, 0, len);
        }

        long endTime = System.currentTimeMillis();
        return endTime - startTime;
    }
```

```java
// 使用 NIO 方法传输文件
    private long transferFileWithNIO(File source, File des) throws IOException {
        long startTime = System.currentTimeMillis();

        if (!des.exists())
            des.createNewFile();

        // 创建随机存取文件对象
        RandomAccessFile read = new RandomAccessFile(source, "rw");
        RandomAccessFile write = new RandomAccessFile(des, "rw");

        // 获取文件通道
        FileChannel readChannel = read.getChannel();
        FileChannel writeChannel = write.getChannel();

        // 创建并使用 ByteBuffer 传输数据
        ByteBuffer byteBuffer = ByteBuffer.allocate(1024 * 1024);
        while (readChannel.read(byteBuffer) > 0) {
            byteBuffer.flip();
            writeChannel.write(byteBuffer);
            byteBuffer.clear();
        }

        // 关闭文件通道
        writeChannel.close();
        readChannel.close();
        long endTime = System.currentTimeMillis();
        return endTime - startTime;
    }
```

```java
    public static void main(String[] args) throws IOException {
        SimpleFileTransferTest simpleFileTransferTest = new SimpleFileTransferTest();
        File sourse = new File("[电影天堂www.dygod.cn]猜火车-cd1.rmvb");
        File des = new File("io.avi");
        File nio = new File("nio.avi");

        // 比较传统的 I/O 和 NIO 传输文件的时间
        long time = simpleFileTransferTest.transferFile(sourse, des);
        System.out.println(time + "：普通字节流时间");

        long timeNio = simpleFileTransferTest.transferFileWithNIO(sourse, nio);
        System.out.println(timeNio + "：NIO时间");
    }
```


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