Java NIO编程

基于Java NIO实现一个客户端和服务端通信的一个流程 客户端通过发送获取当前时间的命令，服务端给出回应。

Java的NIO编程 的确比Java阻塞的IO编程复杂很多 但是对性能的提高是很明显的，今天就是想把JavaNIO熟悉一下以便后续的研究Netty，这样会更好点.

服务端主函数:public class TimeServer { public static void main(String[] args) { int port = 8080; MultiplexerTimeServer timeServer = new MultiplexerTimeServer(port); new Thread(timeServer,"NIO-MultiplexerTimerServer").start(); } } 服务端逻辑代码: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){//因为SocketChannel 设置为non blocking 大于0说明有数据 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); } } } 客户端主函数:public class TimeClient { public static void main(String[] args) { int port = 8080; new Thread(new TimeClientHandle("127.0.0.1", port),"TimeClient").start(); } } 客户端逻辑代码: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){ //执行到这里是发生了异常 所以要把申请的资源释放掉 if(key!=null){ key.cancel(); } if(key.channel()!=null){ key.channel().close(); } } } } catch (IOException e) { e.printStackTrace(); } } //执行到这一步说明 客户端断开了连接 那么就要释放 selector资源 用于多路复用的 底层的实现 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()){//这是连接的请求 if(sc.finishConnect()){//尝试连接 sc.register(selector, SelectionKey.OP_READ); doWrite(sc); }else{ System.exit(1);//连接失败 进程退出 } } if(key.isReadable()){//这说明这个channel上面 服务端写了数据 可读 读之前创建一个缓冲区ByteBuffer ByteBuffer readBuffer = ByteBuffer.allocate(1024);//分配1M的空间 int readBytes = sc.read(readBuffer);//把channel 里的数据读到字节缓冲区里 返回字节数 if(readBytes>0){//因为是异步读的 所以要进判断 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;//读取了时间 接over 线程结束 }else if(readBytes<0){//对端链路已经关闭我 所以我们也进行关闭 key.cancel(); /* * 在服务端是这样实现的 * 服务端是 accept 建立一个SocketChannel * 然后 在进行对那个accept sc 进行操作 所以服务端建立连接是 * 新加的连接 这就是多路复用 但是主的线程却一直没有stop 不能说是主线程 * 其实只有一个线程在处理所有的事情 只是不在主线程里操作的 是新开的一个线程 * */ sc.close();// }else{//读到0个字节 } } } } 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"); } } }

总结:

IO和NIO 也就是阻塞和非阻塞,那么其实在我们实验的过程中因为条件的原因可能感受不到性能的差距，但是真正到了应用的场景，尤其是在并发量很高的情况下，那么NIO的优势也就体现出来了，其实不管是IO还是NIO java一般的读取操作都是通过建立一个缓冲区 然后往缓冲区写或者从缓冲区读。因为读写都是异步的，因为异步是立马返回，不管有没有读到数据，所以我们要根据读的结果来进行相应的处理,如果返回值大于0那么说明读到了数据,所以就可以进行处理;如果返回值小于0，那么说明对端已经关闭了连接，此时也就关闭连接，那么先发起关闭连接的会有time_wait的状态，会等待2个MSL时间,如果返回0那说明读到了0个数据,可以不进行处理。