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传统Socket基于BIO实现一个简单的聊天服务器

服务端代码如下

public class MyServerSocket { public static void main(String[] args) throws IOException { ServerSocket serverSocket = new ServerSocket(); // 绑定5000端口 serverSocket.bind(new InetSocketAddress("127.0.0.1", 5000)); System.out.println("服务端启动成功..."); while (true) { // 如果获取不到socket就会一致阻塞在此 Socket socket = serverSocket.accept(); InputStream is = socket.getInputStream(); byte[] buf = new byte[1024]; int len = is.read(buf); System.out.println("客户端说：" + new String(buf, 0, len, StandardCharsets.UTF_8)); OutputStream os = socket.getOutputStream(); os.write("你好客户端，我收到你的消息了".getBytes(StandardCharsets.UTF_8)); } } } 复制代码

客户端代码如下

public class ClientSocket { public static void main(String[] args) throws IOException { Socket socket = new Socket(); socket.connect(new InetSocketAddress("127.0.0.1",5000)); OutputStream os = socket.getOutputStream(); os.write("hello服务端~".getBytes(StandardCharsets.UTF_8)); InputStream is = socket.getInputStream(); byte[] buf = new byte[1024]; int len = is.read(buf); System.out.println("服务器说：" + new String(buf, 0, len, StandardCharsets.UTF_8)); } } 复制代码

先启动服务器端，再启动客户端。即可

传统BIO是阻塞的，举个烧水的例子来理解

Socket编写一个简单的Http服务器

http服务器的代码

public class HttpServer {
  private static String response = """
      HTTP/1.1 200 OK
      content-type: text/html
            
      <h1>hello,client</h1>
      """;

  public static void main(String[] args) throws IOException {
    ServerSocket serverSocket = new ServerSocket();
    serverSocket.bind(new InetSocketAddress("127.0.0.1", 5001));
    System.out.println("HTTP服务器启动成功");
    while (true) {
      Socket client = serverSocket.accept();
      // 获取客户端发送过来的数据
      InputStream is = client.getInputStream();
      byte[] buf = new byte[1024];
      int len = is.read(buf);
      System.out.println("客户端发送过来的数据：" + new String(buf, 0, len, StandardCharsets.UTF_8));
      // 给客户端响应HTTP协议的数据
      OutputStream os = client.getOutputStream();
      os.write(response.getBytes(StandardCharsets.UTF_8));
      // 注意：要关闭客户端资源
      client.close();
    }
  }
}
复制代码

只要响应数据满足HTTP协议，就可以通过浏览器访问到页面，下面我们使用浏览器访问下

基于NIO的非阻塞简单服务器实现

传统BIO会阻塞，使用NIO通道编程可以设置服务器为非阻塞，当未获取到连接时，可以处理其他的逻辑。相当于线程模型换了。下面是服务端代码，客户端代码不变，采用BIO的即可

public class NioServerSocket { public static void main(String[] args) throws IOException, InterruptedException { ServerSocketChannel serverSocketChannel = ServerSocketChannel.open(); serverSocketChannel.bind(new InetSocketAddress("127.0.0.1", 5002)); serverSocketChannel.configureBlocking(false); // 设置非阻塞 while (true) { SocketChannel clientChannel = serverSocketChannel.accept(); if (clientChannel == null) { System.out.println("客户端无连接，休息一下"); Thread.sleep(1000); continue; } Socket socket = clientChannel.socket(); InputStream is = socket.getInputStream(); byte[] buf = new byte[1024]; int len = is.read(buf); System.out.println("客户端发送过来的数据：" + new String(buf, 0, len, StandardCharsets.UTF_8)); socket.close(); clientChannel.close(); } } } 复制代码

第二种实现方式如下

public class NioServerSocket2 { public static void main(String[] args) throws IOException, InterruptedException { ServerSocketChannel serverSocketChannel = ServerSocketChannel.open(); serverSocketChannel.bind(new InetSocketAddress("127.0.0.1", 5002)); serverSocketChannel.configureBlocking(false); // 设置非阻塞 while (true) { SocketChannel clientChannel = serverSocketChannel.accept(); if (clientChannel == null) { System.out.println("客户端无连接，休息一下"); Thread.sleep(1000); continue; } ByteBuffer buffer = ByteBuffer.allocate(1024); int len = clientChannel.read(buffer); System.out.println("客户端说" + new String(buffer.array(), 0, len)); clientChannel.close(); } } } 复制代码

但是该实现也有一个问题：虽然客户端的连接过程不会阻塞了，但是客户端发送数据会阻塞服务端。如果客户端发送数据过大，假设要10秒，那服务端调用read方法读取数据就要等待客户端至少10秒。

基于NIO的Selector的简单服务器实现

selector的服务端如下，这是要给单线程的服务端。相比上一小节没有使用selector，它的优点就是连接事件和读事件都不会阻塞了。即使客户端发送数据很慢，服务端也不会阻塞。

缺点是单线程执行，如果一个线程抢到读就绪事件并且处理的很慢，就会影响整体性能。

public class NioSelectorServerSocket { public static void main(String[] args) throws Exception { // 1. 获取通道 ServerSocketChannel serverSocketChannel = ServerSocketChannel.open(); serverSocketChannel.bind(new InetSocketAddress("127.0.0.1", 5003)); serverSocketChannel.configureBlocking(false); // 2. 获取选择器 Selector selector = Selector.open(); // 3. 把通道注册到选择器上，只注册连接继续事件 serverSocketChannel.register(selector, SelectionKey.OP_ACCEPT); System.out.println("服务器启动成功..."); while (true) { // 4. 不断轮询选择器中是否由连接事件 int select = selector.select(2000); if (select == 0) { System.out.println("暂时没有客户端连接哦"); continue; } // 5. 如果有连接继续事件，获取客户端通道 Set<SelectionKey> selectionKeys = selector.selectedKeys(); Iterator<SelectionKey> iterator = selectionKeys.iterator(); while (iterator.hasNext()) { SelectionKey key = iterator.next(); if (key.isAcceptable()) { SocketChannel client = serverSocketChannel.accept(); //SocketChannel client = ((ServerSocketChannel) key.channel()).accept(); // 两种写法都一样 client.configureBlocking(false); // 6. 为每个连接都注册写事件监听 client.register(selector, SelectionKey.OP_READ); System.out.println("已注册可读事件"); } if (key.isReadable()) { SocketChannel client = (SocketChannel) key.channel(); // 7. 监听到可读事件，处理可读事件 ByteBuffer buffer = ByteBuffer.allocate(1024); int len = client.read(buffer); System.out.println("客户端说：" + (len > 0 ? new String(buffer.array(), 0, len, StandardCharsets.UTF_8) : "")); // 8. 关闭资源 client.close(); } iterator.remove(); } } } } 复制代码

它的线程模型还是用烧水的例子来举例