Java NIO編程

基於Java NIO實現一個客戶端和服務端通信的一個流程 客戶端通過發送獲取當前時間的命令，服務端給出迴應。

Java的NIO編程 的確比Java阻塞的IO編程複雜很多 但是對性能的提高是很明顯的，今天就是想把JavaNIO熟悉一下以便後續的研究Netty，這樣會更好點.

服務端主函數:public class TimeServer { public static void main(String[] args) { int port = 8080; MultiplexerTimeServer timeServer = new MultiplexerTimeServer(port); new Thread(timeServer,"NIO-MultiplexerTimerServer").start(); } } 服務端邏輯代碼:public class MultiplexerTimeServer implements Runnable{ private Selector selector; private ServerSocketChannel serverChannel; private volatile boolean stop; public MultiplexerTimeServer(int port) { try { selector = Selector.open(); serverChannel = ServerSocketChannel.open(); serverChannel.configureBlocking(false); serverChannel.socket().bind(new InetSocketAddress(port),1024); serverChannel.register(selector, SelectionKey.OP_ACCEPT); System.out.println("The time server has started in port :"+port); } catch (IOException e) { e.printStackTrace(); } } public void stop(){ this.stop = true; } @Override public void run() { while(!stop){ try { selector.select(1000); Set<selectionkey> selectedKeys = selector.selectedKeys(); Iterator<selectionkey> it = selectedKeys.iterator(); SelectionKey key = null; while(it.hasNext()){ key = it.next(); it.remove(); try{ handleInput(key); }catch(Exception e){ if(key!=null){ key.channel(); if(key.channel()!=null){ key.channel().close(); } } } } } catch (IOException e) { e.printStackTrace(); } } if(selector!=null){ try { selector.close(); } catch (IOException e) { e.printStackTrace(); } } } private void handleInput(SelectionKey key) throws IOException{ if(key.isValid()){ //handle 心接入的消息 if(key.isAcceptable()){ ServerSocketChannel ssc = (ServerSocketChannel)key.channel(); try { SocketChannel sc = ssc.accept(); sc.configureBlocking(false); sc.register(selector, SelectionKey.OP_READ); } catch (IOException e) { e.printStackTrace(); } } if(key.isReadable()){ //read the data SocketChannel sc = (SocketChannel) key.channel(); ByteBuffer readBuff = ByteBuffer.allocate(1024); int readBytes = sc.read(readBuff); if(readBytes>0){//因爲SocketChannel 設置爲non blocking 大於0說明有數據 readBuff.flip(); byte[] bytes = new byte[readBuff.remaining()]; readBuff.get(bytes); String body = new String(bytes,"UTF-8"); System.out.println("The Time Server receive order :"+body); String currentTime = "QUERY TIME ORDER".equalsIgnoreCase(body)? new Date(System.currentTimeMillis()).toString():"BAD ORDER"; doWrite(sc,currentTime); }else if(readBytes<0 0="" key="" cancel="" sc="" close="" else="" donothing="" 0="" public="" void="" dowrite="" socketchannel="" channer="" string="" response="" throws="" ioexception="" if="" response="" null="" response="" trim="" length="">0){ byte[] bytes = response.getBytes(); ByteBuffer writeBuffer = ByteBuffer.allocate(bytes.length); writeBuffer.put(bytes); writeBuffer.flip(); channer.write(writeBuffer); } } } 客戶端主函數:public class TimeClient { public static void main(String[] args) { int port = 8080; new Thread(new TimeClientHandle("127.0.0.1", port),"TimeClient").start(); } } 客戶端邏輯代碼:public class TimeClientHandle implements Runnable{ private String host; private int port; private Selector selector; private SocketChannel socketChannel; private volatile boolean stop; public TimeClientHandle(String host, int port) { this.host = host==null?"127.0.0.1":host; this.port = port; try { selector = Selector.open(); socketChannel = SocketChannel.open(); socketChannel.configureBlocking(false); } catch (IOException e) { e.printStackTrace(); } } @Override public void run() { try { doConnect(); } catch (IOException e) { e.printStackTrace(); } while(!stop){ try { selector.select(1000); Set<selectionkey> selectedKeys = selector.selectedKeys(); Iterator<selectionkey> it = selectedKeys.iterator(); SelectionKey key = null; while(it.hasNext()){ key = it.next(); it.remove(); try{ handleInput(key); }catch(Exception e){ //執行到這裏是發生了異常 所以要把申請的資源釋放掉 if(key!=null){ key.cancel(); } if(key.channel()!=null){ key.channel().close(); } } } } catch (IOException e) { e.printStackTrace(); } } //執行到這一步說明 客戶端斷開了連接 那麼就要釋放 selector資源 用於多路複用的 底層的實現 if(selector!=null){ try { selector.close(); } catch (IOException e) { e.printStackTrace(); } } } public void handleInput(SelectionKey key) throws IOException{ if(key.isValid()){ SocketChannel sc = (SocketChannel) key.channel(); if(key.isConnectable()){//這是連接的請求 if(sc.finishConnect()){//嘗試連接 sc.register(selector, SelectionKey.OP_READ); doWrite(sc); }else{ System.exit(1);//連接失敗 進程退出 } } if(key.isReadable()){//這說明這個channel上面 服務端寫了數據 可讀 讀之前創建一個緩衝區ByteBuffer ByteBuffer readBuffer = ByteBuffer.allocate(1024);//分配1M的空間 int readBytes = sc.read(readBuffer);//把channel 裏的數據讀到字節緩衝區裏 返回字節數 if(readBytes>0){//因爲是異步讀的 所以要進判斷 readBuffer.flip(); byte[] bytes = new byte[readBuffer.remaining()]; readBuffer.get(bytes); String body = new String(bytes, "UTF-8"); System.out.println("Now is:"+body); this.stop = true;//讀取了時間 接over 線程結束 }else if(readBytes<0){//對端鏈路已經關閉我 所以我們也進行關閉 key.cancel(); /* * 在服務端是這樣實現的 * 服務端是 accept 建立一個SocketChannel * 然後 在進行對那個accept sc 進行操作 所以服務端建立連接是 * 新加的連接 這就是多路複用 但是主的線程卻一直沒有stop 不能說是主線程 * 其實只有一個線程在處理所有的事情 只是不在主線程裏操作的 是新開的一個線程 * */ sc.close();// }else{//讀到0個字節 } } } } private void doConnect() throws IOException{ if(socketChannel.connect(new InetSocketAddress(host, port))){ socketChannel.register(selector, SelectionKey.OP_READ); doWrite(socketChannel); }else{ socketChannel.register(selector, SelectionKey.OP_CONNECT); } } private void doWrite(SocketChannel sc) throws IOException{ byte[] req = "QUERY TIME ORDER".getBytes(); ByteBuffer writeBuffer = ByteBuffer.allocate(req.length); writeBuffer.put(req); writeBuffer.flip(); sc.write(writeBuffer); if(!writeBuffer.hasRemaining()){ System.out.println("Send Order 2 Server succeed"); } } }

總結:

IO和NIO 也就是阻塞和非阻塞,那麼其實在我們實驗的過程中因爲條件的原因可能感受不到性能的差距，但是真正到了應用的場景，尤其是在併發量很高的情況下，那麼NIO的優勢也就體現出來了，其實不管是IO還是NIO java一般的讀取操作都是通過建立一個緩衝區 然後往緩衝區寫或者從緩衝區讀。因爲讀寫都是異步的，因爲異步是立馬返回，不管有沒有讀到數據，所以我們要根據讀的結果來進行相應的處理,如果返回值大於0那麼說明讀到了數據,所以就可以進行處理;如果返回值小於0，那麼說明對端已經關閉了連接，此時也就關閉連接，那麼先發起關閉連接的會有time_wait的狀態，會等待2個MSL時間,如果返回0那說明讀到了0個數據,可以不進行處理。