NIO下_使用示例

一.分散與聚集

1.分散讀取（Scattering Reads）:將通道中的數據分散到多個緩衝區中

2.聚集寫入（Gathering Writes）:將多個緩衝區中的數據聚集到通道中

public void test4() throws IOException{
        RandomAccessFile raf1 = new RandomAccessFile("1.txt", "rw");
        
        //1. 獲取通道
        FileChannel channel1 = raf1.getChannel();
        
        //2. 分配指定大小的緩衝區
        ByteBuffer buf1 = ByteBuffer.allocate(100);
        ByteBuffer buf2 = ByteBuffer.allocate(1024);
        
        //3. 分散讀取
        ByteBuffer[] bufs = {buf1, buf2};
        channel1.read(bufs);
        
        //4. 聚集寫入
        RandomAccessFile raf2 = new RandomAccessFile("2.txt", "rw");
        FileChannel channel2 = raf2.getChannel();
        
        channel2.write(bufs);
    }

二.字元集Charset

public void test6() throws IOException{
		Charset cs1 = Charset.forName("GBK");
		
		//獲取編碼器
		CharsetEncoder ce = cs1.newEncoder();
		
		//獲取解碼器
		CharsetDecoder cd = cs1.newDecoder();
		
		CharBuffer cBuf = CharBuffer.allocate(1024);
		cBuf.put("字元集！");
		cBuf.flip();
		
		//編碼
		ByteBuffer bBuf = ce.encode(cBuf);
		
		for (int i = 0; i < 12; i++) {
			System.out.println(bBuf.get());
		}
		
		//解碼
		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（選擇器）是Java NIO中能夠檢測一到多個NIO通道，並能夠知曉通道是否為諸如讀寫事件做好準備的組件。這樣，一個單獨的線程可以管理多個channel，從而管理多個網路連接.

1.TCP

eg：客戶端與服務端

//客戶端
	@Test
	public void client() throws IOException{
		//1. 獲取通道
		SocketChannel sChannel = SocketChannel.open(new InetSocketAddress("127.0.0.1", 9898));
		
		//2. 切換非阻塞模式
		sChannel.configureBlocking(false);
		
		//3. 分配指定大小的緩衝區
		ByteBuffer buf = ByteBuffer.allocate(1024);
		
		//4. 發送數據給服務端
		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. 關閉通道
		sChannel.close();
	}

	//服務端
	@Test
	public void server() throws IOException{
		//1. 獲取通道
		ServerSocketChannel ssChannel = ServerSocketChannel.open();
		
		//2. 切換非阻塞模式
		ssChannel.configureBlocking(false);
		
		//3. 綁定連接
		ssChannel.bind(new InetSocketAddress(9898));
		
		//4. 獲取選擇器
		Selector selector = Selector.open();
		
		//5. 將通道註冊到選擇器上, 並且指定“監聽接收事件”
		ssChannel.register(selector, SelectionKey.OP_ACCEPT);
		
		//6. 輪詢式的獲取選擇器上已經“準備就緒”的事件
		while(selector.select() > 0){
			
			//7. 獲取當前選擇器中所有註冊的“選擇鍵(已就緒的監聽事件)”
			Iterator<SelectionKey> it = selector.selectedKeys().iterator();
			
			while(it.hasNext()){
				//8. 獲取準備“就緒”的是事件
				SelectionKey sk = it.next();
				
				//9. 判斷具體是什麼事件準備就緒
				if(sk.isAcceptable()){
					//10. 若“接收就緒”，獲取客戶端連接
					SocketChannel sChannel = ssChannel.accept();
					
					//11. 切換非阻塞模式
					sChannel.configureBlocking(false);
					
					//12. 將該通道註冊到選擇器上
					sChannel.register(selector, SelectionKey.OP_READ);
				}else if(sk.isReadable()){
					//13. 獲取當前選擇器上“讀就緒”狀態的通道
					SocketChannel sChannel = (SocketChannel) sk.channel();
					
					//14. 讀取數據
					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. 取消選擇鍵 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個線程之間的單向數據連接。pipe有一個source管道和一個sink管道。數據會被寫到sink通道，從source通道讀取

public void test1() throws IOException{
		//1. 獲取管道
		Pipe pipe = Pipe.open();
		
		//2. 將緩衝區中的數據寫入管道
		ByteBuffer buf = ByteBuffer.allocate(1024);
		
		Pipe.SinkChannel sinkChannel = pipe.sink();
		buf.put("通過單向管道發送數據".getBytes());
		buf.flip();
		sinkChannel.write(buf);
		
		//3. 讀取緩衝區中的數據
		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();
	}