NIO 有一個(gè)主要的類Selector,這個(gè)類似一個(gè)觀察者，只要我們把需要探知的socketchannel告訴Selector,我們接著做別的事情，當(dāng)有 事件發(fā)生時(shí)，他會(huì)通知我們，傳回一組SelectionKey,我們讀取這些Key,就會(huì)獲得我們剛剛注冊(cè)過(guò)的socketchannel,然后，我們從 這個(gè)Channel中讀取數(shù)據(jù)，放心，包準(zhǔn)能夠讀到，接著我們可以處理這些數(shù)據(jù)。
Selector內(nèi)部原理實(shí)際是在做一個(gè)對(duì)所注冊(cè)的channel的輪詢?cè)L問(wèn)，不斷的輪詢(目前就這一個(gè)算法)，一旦輪詢到一個(gè)channel有所注冊(cè)的事情發(fā)生，比如數(shù)據(jù)來(lái)了，他就會(huì)站起來(lái)報(bào)告，交出一把鑰匙，讓我們通過(guò)這把鑰匙來(lái)讀取這個(gè)channel的內(nèi)容。
jdk供的無(wú)阻塞I/O（NIO）有效解決了多線程服務(wù)器存在的線程開銷問(wèn)題，但在使用上略顯得復(fù)雜一些。在NIO中使用多線程，主要目的已不是為了應(yīng)對(duì) 每個(gè)客戶端請(qǐng)求而分配獨(dú)立的服務(wù)線程，而是通過(guò)多線程充分使用用多個(gè)CPU的處理能力和處理中的等待時(shí)間，達(dá)到提高服務(wù)能力的目的。

server端代碼:

public class HelloWorldServer { static int BLOCK = 1024; static String name = ""; protected Selector selector; protected ByteBuffer clientBuffer = ByteBuffer.allocate(BLOCK); protected CharsetDecoder decoder; static CharsetEncoder encoder = Charset.forName("GB2312").newEncoder(); public HelloWorldServer(int port) throws IOException { selector = this.getSelector(port); Charset charset = Charset.forName("GB2312"); decoder = charset.newDecoder(); } // 獲取Selector protected Selector getSelector(int port) throws IOException { ServerSocketChannel server = ServerSocketChannel.open(); Selector sel = Selector.open(); server.socket().bind(new InetSocketAddress(port)); server.configureBlocking(false); server.register(sel, SelectionKey.OP_ACCEPT); return sel; } // 監(jiān)聽端口 public void listen() { try { for (;;) { selector.select(); Iterator iter = selector.selectedKeys().iterator(); while (iter.hasNext()) { SelectionKey key = (SelectionKey) iter.next(); iter.remove(); process(key); } } } catch (IOException e) { e.printStackTrace(); } } // 處理事件 protected void process(SelectionKey key) throws IOException { if (key.isAcceptable()) { // 接收請(qǐng)求 ServerSocketChannel server = (ServerSocketChannel) key.channel(); SocketChannel channel = server.accept(); //設(shè)置非阻塞模式 channel.configureBlocking(false); channel.register(selector, SelectionKey.OP_READ); } else if (key.isReadable()) { // 讀信息 SocketChannel channel = (SocketChannel) key.channel(); int count = channel.read(clientBuffer); if (count > 0) { clientBuffer.flip(); CharBuffer charBuffer = decoder.decode(clientBuffer); name = charBuffer.toString(); // System.out.println(name); SelectionKey sKey = channel.register(selector, SelectionKey.OP_WRITE); sKey.attach(name); } else { channel.close(); } clientBuffer.clear(); } else if (key.isWritable()) { // 寫事件 SocketChannel channel = (SocketChannel) key.channel(); String name = (String) key.attachment(); ByteBuffer block = encoder.encode(CharBuffer .wrap("Hello !" + name)); channel.write(block); //channel.close(); } } public static void main(String[] args) { int port = 8888; try { HelloWorldServer server = new HelloWorldServer(port); System.out.println("listening on " + port); server.listen(); } catch (IOException e) { e.printStackTrace(); } } }

client端代碼:

public class HelloWorldClient { static int SIZE = 10; static InetSocketAddress ip = new InetSocketAddress("localhost", 8888); static CharsetEncoder encoder = Charset.forName("GB2312").newEncoder(); static class Message implements Runnable { protected String name; String msg = ""; public Message(String index) { this.name = index; } public void run() { try { long start = System.currentTimeMillis(); //打開Socket通道 SocketChannel client = SocketChannel.open(); //設(shè)置為非阻塞模式 client.configureBlocking(false); //打開選擇器 Selector selector = Selector.open(); //注冊(cè)連接服務(wù)端socket動(dòng)作 client.register(selector, SelectionKey.OP_CONNECT); //連接 client.connect(ip); //分配內(nèi)存 ByteBuffer buffer = ByteBuffer.allocate(8 * 1024); int total = 0; _FOR: for (;;) { selector.select(); Iterator iter = selector.selectedKeys().iterator(); while (iter.hasNext()) { SelectionKey key = (SelectionKey) iter.next(); iter.remove(); if (key.isConnectable()) { SocketChannel channel = (SocketChannel) key .channel(); if (channel.isConnectionPending()) channel.finishConnect(); channel .write(encoder .encode(CharBuffer.wrap(name))); channel.register(selector, SelectionKey.OP_READ); } else if (key.isReadable()) { SocketChannel channel = (SocketChannel) key .channel(); int count = channel.read(buffer); if (count > 0) { total += count; buffer.flip(); while (buffer.remaining() > 0) { byte b = buffer.get(); msg += (char) b; } buffer.clear(); } else { client.close(); break _FOR; } } } } double last = (System.currentTimeMillis() - start) * 1.0 / 1000; System.out.println(msg + "used time :" + last + "s."); msg = ""; } catch (IOException e) { e.printStackTrace(); } } } public static void main(String[] args) throws IOException { String names[] = new String[SIZE]; for (int index = 0; index < SIZE; index++) { names[index] = "jeff[" + index + "]"; new Thread(new Message(names[index])).start(); } } }

轉(zhuǎn)載于:https://www.cnblogs.com/itrena/archive/2012/11/18/7434318.html

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