NIO下_使用示例

一.分散与聚集

1.分散读取（Scattering Reads）:将通道中的数据分散到多个缓冲区中

2.聚集写入（Gathering Writes）:将多个缓冲区中的数据聚集到通道中

public void test4() throws IOException{
        RandomAccessFile raf1 = new RandomAccessFile("1.txt", "rw");
        
        //1. 获取通道
        FileChannel channel1 = raf1.getChannel();
        
        //2. 分配指定大小的缓冲区
        ByteBuffer buf1 = ByteBuffer.allocate(100);
        ByteBuffer buf2 = ByteBuffer.allocate(1024);
        
        //3. 分散读取
        ByteBuffer[] bufs = {buf1, buf2};
        channel1.read(bufs);
        
        //4. 聚集写入
        RandomAccessFile raf2 = new RandomAccessFile("2.txt", "rw");
        FileChannel channel2 = raf2.getChannel();
        
        channel2.write(bufs);
    }

二.字符集Charset

public void test6() throws IOException{
		Charset cs1 = Charset.forName("GBK");

		//获取编码器
		CharsetEncoder ce = cs1.newEncoder();

		//获取解码器
		CharsetDecoder cd = cs1.newDecoder();

		CharBuffer cBuf = CharBuffer.allocate(1024);
		cBuf.put("字符集！");
		cBuf.flip();

		//编码
		ByteBuffer bBuf = ce.encode(cBuf);

		for (int i = 0; i < 12; i++) {
			System.out.println(bBuf.get());
		}

		//解码
		bBuf.flip();
		CharBuffer cBuf2 = cd.decode(bBuf);
		System.out.println(cBuf2.toString());

		System.out.println("------------------------------------------------------");

		Charset cs2 = Charset.forName("UTF-8");
		bBuf.flip();
		CharBuffer cBuf3 = cs2.decode(bBuf);
		System.out.println(cBuf3.toString());
	}

三.NIO的非阻塞式(核心：Selector)

Selector（选择器）是Java NIO中能够检测一到多个NIO通道，并能够知晓通道是否为诸如读写事件做好准备的组件。这样，一个单独的线程可以管理多个channel，从而管理多个网络连接.

1.TCP

eg：客户端与服务端

//客户端
	@Test
	public void client() throws IOException{
		//1. 获取通道
		SocketChannel sChannel = SocketChannel.open(new InetSocketAddress("127.0.0.1", 9898));

		//2. 切换非阻塞模式
		sChannel.configureBlocking(false);

		//3. 分配指定大小的缓冲区
		ByteBuffer buf = ByteBuffer.allocate(1024);

		//4. 发送数据给服务端
		Scanner scan = new Scanner(System.in);

		while(scan.hasNext()){
			String str = scan.next();
			buf.put((new Date().toString() + "\n" + str).getBytes());
			buf.flip();
			sChannel.write(buf);
			buf.clear();
		}

		//5. 关闭通道
		sChannel.close();
	}

	//服务端
	@Test
	public void server() throws IOException{
		//1. 获取通道
		ServerSocketChannel ssChannel = ServerSocketChannel.open();

		//2. 切换非阻塞模式
		ssChannel.configureBlocking(false);

		//3. 绑定连接
		ssChannel.bind(new InetSocketAddress(9898));

		//4. 获取选择器
		Selector selector = Selector.open();

		//5. 将通道注册到选择器上, 并且指定“监听接收事件”
		ssChannel.register(selector, SelectionKey.OP_ACCEPT);

		//6. 轮询式的获取选择器上已经“准备就绪”的事件
		while(selector.select() > 0){

			//7. 获取当前选择器中所有注册的“选择键(已就绪的监听事件)”
			Iterator<SelectionKey> it = selector.selectedKeys().iterator();

			while(it.hasNext()){
				//8. 获取准备“就绪”的是事件
				SelectionKey sk = it.next();

				//9. 判断具体是什么事件准备就绪
				if(sk.isAcceptable()){
					//10. 若“接收就绪”，获取客户端连接
					SocketChannel sChannel = ssChannel.accept();

					//11. 切换非阻塞模式
					sChannel.configureBlocking(false);

					//12. 将该通道注册到选择器上
					sChannel.register(selector, SelectionKey.OP_READ);
				}else if(sk.isReadable()){
					//13. 获取当前选择器上“读就绪”状态的通道
					SocketChannel sChannel = (SocketChannel) sk.channel();

					//14. 读取数据
					ByteBuffer buf = ByteBuffer.allocate(1024);

					int len = 0;
					while((len = sChannel.read(buf)) > 0 ){
						buf.flip();
						System.out.println(new String(buf.array(), 0, len));
						buf.clear();
					}
				}

				//15. 取消选择键 SelectionKey
				it.remove();
			}
		}
	}

2.UDP DatagramChannel

public void send() throws IOException{
		DatagramChannel dc = DatagramChannel.open();

		dc.configureBlocking(false);

		ByteBuffer buf = ByteBuffer.allocate(1024);

		Scanner scan = new Scanner(System.in);

		while(scan.hasNext()){
			String str = scan.next();
			buf.put((new Date().toString() + ":\n" + str).getBytes());
			buf.flip();
			dc.send(buf, new InetSocketAddress("127.0.0.1", 9898));
			buf.clear();
		}

		dc.close();
	}

	@Test
	public void receive() throws IOException{
		DatagramChannel dc = DatagramChannel.open();

		dc.configureBlocking(false);

		dc.bind(new InetSocketAddress(9898));

		Selector selector = Selector.open();

		dc.register(selector, SelectionKey.OP_READ);

		while(selector.select() > 0){
			Iterator<SelectionKey> it = selector.selectedKeys().iterator();

			while(it.hasNext()){
				SelectionKey sk = it.next();

				if(sk.isReadable()){
					ByteBuffer buf = ByteBuffer.allocate(1024);

					dc.receive(buf);
					buf.flip();
					System.out.println(new String(buf.array(), 0, buf.limit()));
					buf.clear();
				}
			}

			it.remove();
		}
	}

四.PIpe管道

Java NIO管道是2个线程之间的单向数据连接。pipe有一个source管道和一个sink管道。数据会被写到sink通道，从source通道读取

public void test1() throws IOException{
		//1. 获取管道
		Pipe pipe = Pipe.open();

		//2. 将缓冲区中的数据写入管道
		ByteBuffer buf = ByteBuffer.allocate(1024);

		Pipe.SinkChannel sinkChannel = pipe.sink();
		buf.put("通过单向管道发送数据".getBytes());
		buf.flip();
		sinkChannel.write(buf);

		//3. 读取缓冲区中的数据
		Pipe.SourceChannel sourceChannel = pipe.source();
		buf.flip();
		int len = sourceChannel.read(buf);
		System.out.println(new String(buf.array(), 0, len));

		sourceChannel.close();
		sinkChannel.close();
	}