什么是阻塞IO？

java 代码解读复制代码public class TCPServer {  
  
    public static void main(String[] args) throws IOException {  
        System.out.println("服务的启动...");  
        System.out.println("开始监听9999端口");  
        ServerSocket ss = new ServerSocket(9999);  
        while (true){  
            // 等待客户端连接  
            Socket accept = ss.accept();  
            // 处理客户端请求  
            InputStream is = accept.getInputStream();  
            byte[] b = new byte[10];  
            is.read(b);  
            String clientIP = accept.getInetAddress().getHostAddress();  
            System.out.println(clientIP + "说:" + new String(b));  
            // 回复客户端消息  
            OutputStream os = accept.getOutputStream();  
            os.write("Echo".getBytes());  
            // 关闭  
            accept.close();  
        }  
    }  
}

java 代码解读复制代码public class TCPClient {  
    public static void main(String[] args) throws IOException {  
        while (true){  
            //创建socket对象  
            Socket s = new Socket("127.0.0.1", 9999);  
            OutputStream os = s.getOutputStream();  
            System.out.println("请输入：");  
            Scanner sc = new Scanner(System.in);  
            String input = sc.nextLine();  
            os.write(input.getBytes());  
            //获得服务端的响应  
            byte[] b = new byte[1024];  
            int len = s.getInputStream().read(b);  
            System.out.println("服务端回复：" + new String(b, 0, len));  
            //关闭连接  
            s.close();  
        }  
    }  
}