第一章 java nio三大組件與使用姿勢
本案例來源於《netty權威指南》
一、三大組件
- Selector：多路復用器。輪詢註冊在其上的Channel，當發現某個或者多個Channel處於“就緒狀態”後（accept接收連接事件、connect連接完成事件、read讀事件、write寫事件），從阻塞狀態返回就緒的Channel的SelectionKey集合，之後進行IO操作。
- Channel：封裝了socket。
- ServerSocketChannel：封裝了ServerSocket，用於accept客戶端連接請求；
- SocketChannel：一對SocketChannel組成一條虛電路，進行讀寫通信
- Buffer：用於存取數據，最主要的是ByteBuffer
- position：下一個將被操作的字節位置
- limit：在寫模式下表示可以進行寫的字節數，在讀模式下表示可以進行讀的字節數
- capacity：Buffer的大小
二、服務端代碼
1、服務端啟動類
1 public class Server { 2 public static void main(String[] args) throws IOException { 3 new Thread(new ServerHandler(8080), "server-1").start(); 4 } 5 }
創建一個任務ServerHandler，然後創建一條線程，啟動執行該任務。
2、邏輯處理類
1public class ServerHandler implements Runnable { 2 private Selector selector; 3 private ServerSocketChannel ssChannel; 4 5 public ServerHandler(int port) { 6 try { 7 //等價於 Selector selector = SelectorProvider.provider().openSelector(); 8 selector = Selector.open();9 //等價於 SelectorProvider.provider().openServerSocketChannel() 10 ssChannel = ServerSocketChannel.open(); 11 ssChannel.configureBlocking(false); 12 ssChannel.bind(new InetSocketAddress(port), 1024); 13 ssChannel.register(selector, SelectionKey.OP_ACCEPT); 14 } catch (IOException e) { 15 e.printStackTrace(); 16 System.exit(1); 17 } 18 } 19 20 public void run() { 21 for (; ; ) { 22 try { 23 selector.select(); 24 Iterator<SelectionKey> it = selector.selectedKeys().iterator(); 25 while (it.hasNext()) { 26 SelectionKey key = it.next(); 27 it.remove(); 28 handleInput(key); 29 } 30 } catch (Throwable t) { 31 t.printStackTrace(); 32 } 33 } 34 35 } 36 37 private void handleInput(SelectionKey key) throws IOException { 38 if (key.isValid()) { 39 // 處理新接入的請求消息 40 if (key.isAcceptable()) { 41 // Accept the new connection 42 ServerSocketChannel ssc = (ServerSocketChannel) key.channel(); 43 SocketChannel sc = ssc.accept(); 44 sc.configureBlocking(false); 45 // Add the new connection to the selector 46 sc.register(selector, SelectionKey.OP_READ); 47 } 48 if (key.isReadable()) { 49 // Read the data 50 SocketChannel sc = (SocketChannel) key.channel(); 51 ByteBuffer readBuffer = ByteBuffer.allocate(1024); 52 int readBytes = sc.read(readBuffer); 53 if (readBytes > 0) { 54 readBuffer.flip(); 55 byte[] bytes = new byte[readBuffer.remaining()]; 56 readBuffer.get(bytes); 57 String body = new String(bytes, "UTF-8"); 58 System.out.println("The time server receive order : " 59 + body); 60 String currentTime = "QUERY TIME ORDER" 61 .equalsIgnoreCase(body) ? new java.util.Date( 62 System.currentTimeMillis()).toString() 63 : "BAD ORDER"; 64 doWrite(sc, currentTime); 65 } else if (readBytes < 0) { 66 // 對端鏈路關閉 67 key.cancel(); 68 sc.close(); 69 } else 70 ; // 讀到0字節，忽略 71 } 72 } 73 } 74 75 private void doWrite(SocketChannel channel, String response) 76 throws IOException { 77 if (response != null && response.trim().length() > 0) { 78 byte[] bytes = response.getBytes(); 79 ByteBuffer writeBuffer = ByteBuffer.allocate(bytes.length); 80 writeBuffer.put(bytes); 81 writeBuffer.flip(); 82 channel.write(writeBuffer); 83 } 84 } 85 }
步驟：
1、創建一個Selector和ServerSocketChannel實例
2、配置ServerSocketChannel實例為非阻塞
3、ServerSocketChannel實例bind端口
4、將ServerSocketChannel實例註冊到selector上，監聽OP_ACCEPT事件
下面的任務在Server創建的新的線程中執行，不影響主線程執行其他邏輯
5、之後進入死循環
5.1、使用select.select()阻塞等待就緒事件（這裏是等待OP_ACCEPT事件），一旦有有就緒事件到達，立即向下執行
5.2、使用selector.selectedKeys()獲取已經就緒的SelectionKey（即OP_ACCEPT/OP_CONECT/OP_READ/OP_WRITE）集合，之後循環遍歷
5.3、從叠代器刪除該SelectionKey，防止下一次再被遍歷到
5.4、如果SelectionKey==OP_ACCEPT，則通過ServerSocketChannel.accept()創建SocketChannel，該SocketChannel是後續真正的與客戶端的SocketChannel進行通信的實體
5.5、配置新創建的SocketChannel實例為非阻塞，然後將該SocketChannel實例註冊到selector實例上，監聽OP_READ事件
5.6、等客戶端發出請求數據時，此處監聽到SelectionKey==OP_READ，則創建ByteBuffer實例，將SocketChannel中的數據讀取到ByteBuffer中，然後再創建ByteBuffer將信息寫回到SocketChannel（也就是說數據的讀寫一定要通過Buffer）
三、客戶端代碼
1、客戶端啟動類
1 public class Client { 2 public static void main(String[] args) { 3 new Thread(new ClientHandler("127.0.0.1", 8080), "client-1").start(); 4 } 5 }
創建一個任務ClientHandler，然後創建一條線程，啟動執行該任務。
2、邏輯處理類
1 public class ClientHandler implements Runnable { 2 private String host; 3 private int port; 4 5 private Selector selector; 6 private SocketChannel socketChannel; 7 8 public ClientHandler(String host, int port) { 9 this.host = host; 10 this.port = port; 11 try { 12 selector = Selector.open(); 13 socketChannel = SocketChannel.open(); 14 socketChannel.configureBlocking(false); 15 } catch (IOException e) { 16 e.printStackTrace(); 17 System.exit(1); 18 } 19 } 20 21 public void run() { 22 try { 23 doConnect(); 24 } catch (IOException e) { 25 e.printStackTrace(); 26 System.exit(1); 27 } 28 while (true) { 29 try { 30 selector.select(); 31 Iterator<SelectionKey> it = selector.selectedKeys().iterator(); 32 while (it.hasNext()) { 33 SelectionKey key = it.next(); 34 it.remove(); 35 handleInput(key); 36 } 37 } catch (Exception e) { 38 e.printStackTrace(); 39 System.exit(1); 40 } 41 } 42 } 43 44 private void handleInput(SelectionKey key) throws IOException { 45 if (key.isValid()) { 46 // 判斷是否連接成功 47 SocketChannel sc = (SocketChannel) key.channel(); 48 if (key.isConnectable()) { 49 if (sc.finishConnect()) { 50 sc.register(selector, SelectionKey.OP_READ); 51 doWrite(sc); 52 } else 53 System.exit(1);// 連接失敗，進程退出 54 } else if (key.isReadable()) { 55 ByteBuffer readBuffer = ByteBuffer.allocate(1024); 56 int readBytes = sc.read(readBuffer); 57 if (readBytes > 0) { 58 readBuffer.flip(); 59 byte[] bytes = new byte[readBuffer.remaining()]; 60 readBuffer.get(bytes); 61 String body = new String(bytes, "UTF-8"); 62 System.out.println("Now is : " + body); 63 } else if (readBytes < 0) { 64 // 對端鏈路關閉 65 key.cancel(); 66 sc.close(); 67 } else 68 ; // 讀到0字節，忽略 69 } 70 } 71 72 } 73 74 private void doConnect() throws IOException { 75 // 如果直接連接成功，則註冊到多路復用器上，發送請求消息，讀應答 76 if (socketChannel.connect(new InetSocketAddress(host, port))) { 77 socketChannel.register(selector, SelectionKey.OP_READ); 78 doWrite(socketChannel); 79 } else 80 socketChannel.register(selector, SelectionKey.OP_CONNECT); 81 } 82 83 private void doWrite(SocketChannel sc) throws IOException { 84 byte[] req = "QUERY TIME ORDER".getBytes(); 85 ByteBuffer writeBuffer = ByteBuffer.allocate(req.length); 86 writeBuffer.put(req); 87 writeBuffer.flip(); 88 sc.write(writeBuffer); 89 if (!writeBuffer.hasRemaining()) 90 System.out.println("Send order 2 server succeed."); 91 } 92 }
步驟：
1、創建一個Selector和SocketChannel實例
2、配置SocketChannel實例為非阻塞
下面的任務在Cilent創建的新的線程中執行，不影響主線程執行其他邏輯
3、SocketChannel.connect連接到server端，如果連接沒有馬上成功，將該SocketChannel實例註冊到selector上，監聽OP_CONNECT事件；如果連接成功，將該SocketChannel實例註冊到selector上，監聽OP_READ事件，之後寫數據給server端
4、之後進入死循環
4.1、使用select.select()阻塞等待就緒事件，一旦有有就緒事件到達，立即向下執行
4.2、使用selector.selectedKeys()獲取已經就緒的SelectionKey（即OP_ACCEPT/OP_CONECT/OP_READ/OP_WRITE）集合，之後循環遍歷
4.3、從叠代器刪除該SelectionKey，防止下一次再被遍歷到
4.4、如果SelectionKey==OP_CONNECT，將該SocketChannel實例註冊到selector上，監聽OP_READ事件，之後寫數據給server端；如果監聽到SelectionKey==OP_READ，則創建ByteBuffer實例，將SocketChannel中的數據讀取到ByteBuffer中
第一章 java nio三大組件與使用姿勢