NIO同步网络编程

淩亂°似流年 2022-12-01 11:57 292阅读 0赞

NIO核心三大组件Channel、Buffer和Selector，传送门：

[Java NIO核心三大组件Channel、Buffer和Selector（一）][Java NIO_Channel_Buffer_Selector]

[Java NIO核心三大组件Channel、Buffer和Selector（二）][Java NIO_Channel_Buffer_Selector 1]

NIO主要有：

*  FileChannel   连接到文件的通道，它无法设置为非阻塞模式，它总是运行在阻塞模式下。
 *  ServerSocketChannel  监听新进来的TCP连接的通道，对应前面的服务器端ServerSocket
 *  SocketChannel    连接到TCP网络套接字的通道，对应前面的客户端Socket
 *  DatagramChannel  连接到UDP包的通道

FileChannel在NIO上面认识过了，这里主要用ServerSocketChannel 和SocketChannel 来进行网络编程。

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### 一、ServerSocketChannel和SocketChannel类 ###

**1、ServerSocketChannel 对象**

NIO中的 ServerSocketChannel 是一个可以监听新进来的TCP连接的通道, 类似于ServerSocket，它们的用法比较类似。

*   *  <table> 
         <tbody> 
          <tr> 
           <td><code>abstract <a rel="nofollow">SocketChannel</a></code></td> 
           <td><code><a rel="nofollow">accept</a>()</code> <p>接受这个通道的套接字的连接。</p> </td> 
          </tr> 
          <tr> 
           <td><code><a rel="nofollow">ServerSocketChannel</a></code></td> 
           <td><code><a rel="nofollow">bind</a>(<a rel="nofollow">SocketAddress</a>&nbsp;local)</code> <p>结合通道的插座到本地地址和配置套接字监听连接。</p> </td> 
          </tr> 
          <tr> 
           <td><code>abstract <a rel="nofollow">ServerSocketChannel</a></code></td> 
           <td><code><a rel="nofollow">bind</a>(<a rel="nofollow">SocketAddress</a>&nbsp;local, int&nbsp;backlog)</code> <p>结合通道的插座到本地地址和配置套接字监听连接。</p> </td> 
          </tr> 
          <tr> 
           <td><code>abstract <a rel="nofollow">SocketAddress</a></code></td> 
           <td><code><a rel="nofollow">getLocalAddress</a>()</code> <p>返回此通道的套接字绑定到的套接字地址。</p> </td> 
          </tr> 
          <tr> 
           <td><code>static <a rel="nofollow">ServerSocketChannel</a></code></td> 
           <td><code><a rel="nofollow">open</a>()</code> <p>打开服务器套接字通道。</p> </td> 
          </tr> 
          <tr> 
           <td><code>abstract &lt;T&gt;&nbsp;<a rel="nofollow">ServerSocketChannel</a></code></td> 
           <td><code><a rel="nofollow">setOption</a>(<a rel="nofollow">SocketOption</a>&lt;T&gt;&nbsp;name, T&nbsp;value)</code> <p>设置套接字选项的值。</p> </td> 
          </tr> 
          <tr> 
           <td><code>abstract <a rel="nofollow">ServerSocket</a></code></td> 
           <td><code><a rel="nofollow">socket</a>()</code> <p>检索与此通道关联的服务器套接字。</p> </td> 
          </tr> 
         </tbody> 
        </table>

accept() 方法监听新进来的连接，返回一个新进来的连接的 SocketChannel。

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**1. 阻塞模式**

通常在while循环中调用 accept()方法，一直监听，因此, accept()方法会一直阻塞到有新连接到达。如：

while (true) {
                SocketChannel socketChannel = serverSocketChannel.accept();
                //do something
            }

**2. 非阻塞模式**

ServerSocketChannel可以设置成非阻塞模式。

在非阻塞模式下，accept() 方法会立刻返回，如果还没有新进来的连接，立即返回null。 因此，需要检查返回的SocketChannel是否是null。如：

ServerSocketChannel serverSocketChannel = ServerSocketChannel.open();
            serverSocketChannel.socket().bind(new InetSocketAddress("127.0.0.1", 9999));
            serverSocketChannel.configureBlocking(false);
            while (true) {
                SocketChannel socketChannel = serverSocketChannel.accept();
                if (socketChannel != null) {
                    //do something 
                }
            }

**2、SocketChannel 对象**

NIO中的SocketChannel是一个连接到TCP网络套接字的通道。类似于ServerSocket，它们的用法比较类似。

*   *  <table> 
         <tbody> 
          <tr> 
           <td><code>abstract <a rel="nofollow">SocketChannel</a></code></td> 
           <td><code><a rel="nofollow">bind</a>(<a rel="nofollow">SocketAddress</a>&nbsp;local)</code> <p>将信道的套接字绑定到本地地址。</p> </td> 
          </tr> 
          <tr> 
           <td><code>abstract boolean</code></td> 
           <td><code><a rel="nofollow">connect</a>(<a rel="nofollow">SocketAddress</a>&nbsp;remote)</code> <p>连接这个通道的插座。</p> </td> 
          </tr> 
          <tr> 
           <td><code>abstract boolean</code></td> 
           <td><code><a rel="nofollow">finishConnect</a>()</code> <p>完成了一个套接字通道的连接的过程。</p> </td> 
          </tr> 
          <tr> 
           <td><code>abstract <a rel="nofollow">SocketAddress</a></code></td> 
           <td><code><a rel="nofollow">getLocalAddress</a>()</code> <p>返回此通道的套接字绑定到的套接字地址。</p> </td> 
          </tr> 
          <tr> 
           <td><code>abstract <a rel="nofollow">SocketAddress</a></code></td> 
           <td><code><a rel="nofollow">getRemoteAddress</a>()</code> <p>返回此通道的套接字连接的远程地址。</p> </td> 
          </tr> 
          <tr> 
           <td><code>abstract boolean</code></td> 
           <td><code><a rel="nofollow">isConnected</a>()</code> <p>告诉是否该通道的网络套接字连接。</p> </td> 
          </tr> 
          <tr> 
           <td><code>abstract boolean</code></td> 
           <td><code><a rel="nofollow">isConnectionPending</a>()</code> <p>告诉是否该通道的连接操作正在进行中。</p> </td> 
          </tr> 
          <tr> 
           <td><code>static <a rel="nofollow">SocketChannel</a></code></td> 
           <td><code><a rel="nofollow">open</a>()</code> <p>打开一个套接字通道。</p> </td> 
          </tr> 
          <tr> 
           <td><code>static <a rel="nofollow">SocketChannel</a></code></td> 
           <td><code><a rel="nofollow">open</a>(<a rel="nofollow">SocketAddress</a>&nbsp;remote)</code> <p>打开一个套接字通道，并将其连接到远程地址。</p> </td> 
          </tr> 
         </tbody> 
        </table>

connect() 连接服务器端。

![watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3FxXzQyNDAyODU0_size_16_color_FFFFFF_t_70 2][]

**1. 非阻塞模式**

如果SocketChannel在非阻塞模式下，此时调用connect()，该方法可能在连接建立之前就返回了。

为了确定连接是否建立，可以调用finishConnect()的方法。如：

socketChannel.configureBlocking(false);
            socketChannel.connect(new InetSocketAddress("127.0.0.1", 9999));
            while (!socketChannel.finishConnect()) {
                //wait 等待连接
            }

**3、非阻塞模式与选择器**

非阻塞模式与选择器搭配会工作的更好，通过将一或多个SocketChannel注册到Selector，可以询问选择器哪个通道的兴趣事件来进行连接就绪，读取，写入等。

### 二、NIO同步网络编程 ###

服务端：

public class SimpleServer {
        public static void main(String[] args) {
            try {
                // 获取一个serverSocketChannel，并设置为非阻塞模式,绑定ip和port
                ServerSocketChannel serverSocketChannel = ServerSocketChannel.open();
                serverSocketChannel.configureBlocking(false);
                ServerSocket serverSocket = serverSocketChannel.socket();
                serverSocket.bind(new InetSocketAddress("127.0.0.1", 9999));
    
                // 获取Selector，注册,并将 ServerSocketChannel 的接收就绪事件通道注册到 Selector
                Selector selector = Selector.open();
                serverSocketChannel.register(selector, SelectionKey.OP_ACCEPT);
    
                // 缓冲区， 写点数据
                ByteBuffer readBuffer = ByteBuffer.allocate(1024);
                ByteBuffer writeBuffer = ByteBuffer.allocate(100);
                writeBuffer.put("服务器端收到了".getBytes());
                writeBuffer.flip();
    
                // 使用循环不断地监听来自客户端的连接
                while (true){
                    int count = selector.select(1000);
                    if (count == 0) {
                        continue;
                    }
                    Set<SelectionKey> keys = selector.selectedKeys();
                    Iterator<SelectionKey> it = keys.iterator();
    
                    while(it.hasNext()){
                        SelectionKey key = it.next();
                        it.remove();// 手动移除
    
                        if(key.isAcceptable()){
                            // 接收就绪，创建新的连接，并且把连接注册到Selector上，并且指定感兴趣的事件是 Accept
                            SocketChannel socketChannel = serverSocketChannel.accept();
                            socketChannel.configureBlocking(false);
                            // 这里我们指定 Server先读，Client先写
                            socketChannel.register(selector, SelectionKey.OP_READ);
                        }else if (key.isReadable()){
                            SocketChannel socketChannel = (SocketChannel) key.channel();
                            readBuffer.clear();
                            socketChannel.read(readBuffer);
                            readBuffer.flip();
                            System.out.println("服务器received：" + new String(readBuffer.array()));
    
                            key.interestOps(SelectionKey.OP_WRITE);
                        }else if(key.isWritable()){
                            SocketChannel socketChannel = (SocketChannel) key.channel();
                            writeBuffer.rewind();
                            socketChannel.write(writeBuffer);
                            key.interestOps(SelectionKey.OP_READ);
                        }
                    }
                }
            } catch (IOException ioException) {
                ioException.printStackTrace();
            }
    
        }
    }

客户端：

public class SimpleClient {
    
        public static void main(String[] args) {
            try {
                // 创建一个SocketChannel，并设置为非阻塞模式,绑定ip和port
                // 获取Selector，注册，并将 socketChannel 的连接事件通道注册到 Selector
                // 并向服务器发出连接请求
                SocketChannel socketChannel = SocketChannel.open();
                socketChannel.configureBlocking(false);
                Selector selector = Selector.open();
                socketChannel.register(selector, SelectionKey.OP_CONNECT);
                socketChannel.connect(new InetSocketAddress("127.0.0.1", 9999));
    
                // 缓冲区， 写点数据
                ByteBuffer readBuffer = ByteBuffer.allocate(1024);
                ByteBuffer writeBuffer = ByteBuffer.allocate(100);
    
                // 使用一个循环来连接服务器
                while (true) {
                    int count = selector.select(5000);
                    if (count == 0) {
                        continue;
                    }
                    Set<SelectionKey> selectionKeys = selector.selectedKeys();
                    Iterator<SelectionKey> it = selectionKeys.iterator();
                    while (it.hasNext()) {
                        SelectionKey selectionKey = it.next();
                        it.remove();
                        if (selectionKey.isConnectable()) {
                            SocketChannel sc = (SocketChannel) selectionKey.channel();
                            if (socketChannel.isConnectionPending()) {
                                if (sc.finishConnect()) {
                                    writeBuffer.put("客户端向你问好".getBytes());
                                    writeBuffer.flip();
                                    sc.write(writeBuffer);
                                    // 改变选择器对通道的兴趣事件, 两种方式都可以，二选一
                                    //socketChannel.register(selector, SelectionKey.OP_READ);
                                    selectionKey.interestOps(SelectionKey.OP_READ);
                                } else {
                                    System.exit(1);
                                }
                            }
                        } else if (selectionKey.isReadable()) {
                            int readBytes = socketChannel.read(readBuffer);
                            if (readBytes > 0) {
                                socketChannel.read(readBuffer);
                                readBuffer.flip();
                                System.out.println("客户端received：" + new String(readBuffer.array()));
                            }
                        }
    
                    }
                }
            } catch (
                    IOException ioException) {
                ioException.printStackTrace();
            }
        }
    }

这篇博主通过线程的实例代码不错，可以参考：[IO模型之NIO代码及其实践详解][IO_NIO]

—— Stay Hungry. Stay Foolish. 求知若饥，虚心若愚。

[Java NIO_Channel_Buffer_Selector]: https://blog.csdn.net/qq_42402854/article/details/107536448
[Java NIO_Channel_Buffer_Selector 1]: https://blog.csdn.net/qq_42402854/article/details/107622273
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[watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3FxXzQyNDAyODU0_size_16_color_FFFFFF_t_70 1]: /images/20221123/eb5016821f35461a9907abb74158890b.png
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[IO_NIO]: https://www.cnblogs.com/jing99/p/12000371.html