[Day 2] Java 程序员修炼之道学习笔记

1. 异步I/O操作

   • 异步I/O-将来式

     public static void main(String[] args) {
         try {
             Path file = Paths.get("/usr/karianna/foobar.txt");
             //异步打开文件
             AsynchronousFileChannel channel = AsynchronousFileChannel
                     .open(file);
     
             ByteBuffer buffer = ByteBuffer.allocate(100_000);
             Future<Integer> result = channel.read(buffer, 0);
             //判断result是否结束
             while (!result.isDone()) {
                 ProfitCalculator.calculateTax();
             }
     
             Integer bytesRead = result.get();
             System.out.println("Bytes read [" + bytesRead + "]");
         } catch (IOException | ExecutionException | InterruptedException e) {
             System.out.println(e.getMessage());
         }
     }
     
     private static class ProfitCalculator {
     
         public ProfitCalculator() {
         }
     
         public static void calculateTax() {
         }
     }

   • 异步I/O-回调式

     public static void main(String[] args) {
         try {
             Path file = Paths.get("/usr/karianna/foobar.txt");
             AsynchronousFileChannel channel = AsynchronousFileChannel
                     .open(file);
     
             ByteBuffer buffer = ByteBuffer.allocate(100_000);
     
             channel.read(buffer, 0, buffer,
                     new CompletionHandler<Integer, ByteBuffer>() {
     
                         @Override
                         public void completed(Integer result,
                                 ByteBuffer attachment) {
                             System.out.println("Bytes read [" + result + "]");
                         }
     
                         @Override
                         public void failed(Throwable exception,
                                 ByteBuffer attachment) {
                             System.out.println(exception.getMessage());
                         }
                     });
         } catch (IOException e) {
             System.out.println(e.getMessage());
         }
     }

2. NetworkChannel
   获取当前主机networkinterface列表

   public static void main(String[] args) {
           try {
               Enumeration<NetworkInterface> interfaceList = NetworkInterface
                       .getNetworkInterfaces();
               if (null == interfaceList) {
                   System.out.println("--No intercaces found--");
               } else {
                   while (interfaceList.hasMoreElements()) {
                       NetworkInterface iface = interfaceList.nextElement();
                       System.out.println("Interface " + iface.getName() + ":");
                       Enumeration<InetAddress> addrList = iface
                               .getInetAddresses();
                       if (!addrList.hasMoreElements()) {
                           System.out
                                   .println("\t(No addresses for this interface)");
                       }
                       while (addrList.hasMoreElements()) {
                           InetAddress address = addrList.nextElement();
                           System.out
                                   .print("\tAddress "
                                           + ((address instanceof Inet4Address ? "(v4)"
                                                   : (address instanceof Inet6Address ? "(v6)"
                                                           : "(?)"))));
                           System.out.println(": " + address.getHostAddress());
                       }
                   }
               }
           } catch (SocketException se) {
               System.out.println("Error getting network interfaces:"
                       + se.getMessage());
           }
      }