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要素

  1. 两个主要的问题：如何准确定位到网络上的一台或多台主机；找到主机之后如何通信。
  2. 网络编程中的要素：IP和端口号；网络通信协议。
  3. 万物皆对象。

IP

  • IP地址：InterAddress，唯一定位一台网络上的计算机。
  • 127.0.0.1：本机localhost。
  • ip地址分类：
    • ipv4 / ipv6
    • 公网（互联网）-私网（局域网）
  • 域名：记忆IP问题
public class TestIP {
   public static void main(String[] args) {
      try {
         InetAddress inetAddress1 = InetAddress.getLocalHost();
         System.out.println(inetAddress1);
         InetAddress inetAddress2 = InetAddress.getByName("www.baidu.com");
         System.out.println(inetAddress2);
         System.out.println(inetAddress2.getCanonicalHostName());//规范的名字
         System.out.println(inetAddress2.getHostAddress());//ip
         System.out.println(inetAddress2.getHostName());//域名
      } catch (UnknownHostException e) {
         e.printStackTrace();
      }
   }
}

端口

不同的端口有不同的端口号，用来区分软件。

0-65535被规定。单个协议下，端口号不能冲突。

端口分类：

  • 公用端口 0-1023
    • HTTP: 80
    • HTTPS: 443
    • FTP: 21
    • Telent: 23
  • 程序注册端口 1024-49151，分配用户或者程序
    • Tomcat: 8080
    • MySQL: 3306
    • Oracle: 1521
  • 动态、私有 49152-65535
netstat -ano #查看所有端口
netstat -ano|findstr "10000" #查看指定端口
tasklist|findstr "10000" #查看指定端口的进程
public class TestSocket {
   public static void main(String[] args) {
      InetSocketAddress socketAddress = new InetSocketAddress("127.0.0.1", 8080);
      InetSocketAddress socketAddress2 = new InetSocketAddress("localhost", 8080);
      System.out.println(socketAddress);
      System.out.println(socketAddress2);

      System.out.println(socketAddress.getAddress());
      System.out.println(socketAddress.getHostName()); //地址
      System.out.println(socketAddress.getPort()); //端口
   }
}

通信协议

网络通信协议：速率、传输码率、代码结构、传输控制……

TCP用户传输协议 UDP用户数据报协议
连接，稳定 不连接，不稳定
客户端、服务端 没有明确的界限
三次握手，四次挥手 不管是否准备好，都可以发
传输完成，释放连接，效率低 DDOS攻击、饱和攻击

TCP实现聊天

//服务端
public class TCPServerDemo1 {
   public static void main(String[] args) {
      try (ServerSocket serverSocket = new ServerSocket(9999);
           Socket socket = serverSocket.accept();
           InputStream is = socket.getInputStream();
           ByteArrayOutputStream baos = new ByteArrayOutputStream()
      ) {
         byte[] buffer = new byte[1024];
         int len;
         while ((len = is.read(buffer)) != -1) {
            baos.write(buffer, 0, len);
         }
         System.out.println(baos);
      } catch (IOException e) {
         e.printStackTrace();
      }
   }
}
//客户端
public class TCPClientDemo1 {
   public static void main(String[] args) {
      Socket socket = null;
      OutputStream os = null;
      try {
         InetAddress serverIP = InetAddress.getByName("127.0.0.1");
         socket = new Socket(serverIP, 9999);
         os = socket.getOutputStream();
         os.write("nb".getBytes());
      } catch (IOException e) {
         e.printStackTrace();
      } finally {
         if (os != null) {
            try {
               os.close();
            } catch (IOException e) {
               e.printStackTrace();
            }
         }
         if (socket != null) {
            try {
               socket.close();
            } catch (IOException e) {
               e.printStackTrace();
            }
         }
      }
   }
}

客户端使用的是比较冗长的写法，将各种资源的close()方法写在finally块中，同时加入各自的catch块。服务端使用的是try-with-resources语句，更简洁。

如果需要服务端不断监听并收取消息，需使用循环语句改写代码。

Java——IO流超详细总结

TCP实现文件上传

//服务端
public class TCPServerDemo2 {
   public static void main(String[] args) {
      try (ServerSocket serverSocket = new ServerSocket(9000);
           Socket socket = serverSocket.accept(); //阻塞式监听
           InputStream is = socket.getInputStream();
           OutputStream os = socket.getOutputStream();
           FileOutputStream fos = new FileOutputStream("receive.jpg")) {
         //接收文件
         byte[] buffer = new byte[1024];
         int len;
         while ((len = is.read(buffer)) != -1) {
            fos.write(buffer, 0, len);
         }
         os.write("Received".getBytes()); //通知客户端已接收完毕
      } catch (IOException e) {
         e.printStackTrace();
      }
   }
}
//客户端
public class TCPClientDemo2 {
   public static void main(String[] args) {
      try (Socket socket = new Socket(InetAddress.getByName("127.0.0.1"), 9000);
           InputStream is = socket.getInputStream();
           OutputStream os = socket.getOutputStream();
           FileInputStream fis = new FileInputStream("hitpt.jpg");
           ByteArrayOutputStream baos = new ByteArrayOutputStream()) {
         //发送文件
         byte[] buffer = new byte[1024];
         int len;
         while ((len = fis.read(buffer)) != -1) {
            os.write(buffer, 0, len);
         }
         socket.shutdownOutput(); //表示发送完了
         System.out.println("Sent");
         //等待服务端通知接收完毕
         while ((len = is.read(buffer)) != -1) {
            baos.write(buffer, 0, len);
         }
         System.out.println("Server: " + baos);
      } catch (IOException e) {
         e.printStackTrace();
      }
   }
}

UDP

连续发送消息

public class UDPSenderDemo {
   public static void main(String[] args) {
      try (DatagramSocket socket = new DatagramSocket(8888);
           BufferedReader reader = new BufferedReader(new InputStreamReader(System.in))) {
         while (true) {
            String dataString = reader.readLine();
            byte[] data = dataString.getBytes();
            DatagramPacket packet = new DatagramPacket(data, 0, data.length, new InetSocketAddress("localhost", 6666));
            socket.send(packet);
            if (dataString.equals("bye")) {
               break;
            }
         }
      } catch (IOException e) {
         e.printStackTrace();
      }
   }
}
import java.io.IOException;
import java.net.DatagramPacket;
import java.net.DatagramSocket;

public class UDPReceiverDemo {
   public static void main(String[] args) {
      try (DatagramSocket socket = new DatagramSocket(6666)) {
         while (true) {
            byte[] container = new byte[1024];
            DatagramPacket packet = new DatagramPacket(container, 0, container.length);
            socket.receive(packet); //阻塞式接收包裹
            String data = new String(packet.getData(), 0, packet.getLength());
            System.out.println(packet.getSocketAddress() + " --> " + data);
            if (data.equals("bye")) {
               break;
            }
         }
      } catch (IOException e) {
         e.printStackTrace();
      }
   }
}

两端平等，无C/S概念。

聊天工具实现

基于上例，再利用多线程来实现。

public class TalkSend implements Runnable {
   DatagramSocket socket = null;
   BufferedReader reader = null;

   private final String toIP;
   private final int toPort;

   public TalkSend(String toIP, int fromPort, int toPort) {
      this.toIP = toIP;
      this.toPort = toPort;
      try {
         this.socket = new DatagramSocket(fromPort);
         this.reader = new BufferedReader(new InputStreamReader(System.in));
      } catch (SocketException e) {
         e.printStackTrace();
      }
   }

   @Override
   public void run() {
      while (true) {
         try {
            String dataString = this.reader.readLine();
            byte[] data = dataString.getBytes();
            DatagramPacket packet = new DatagramPacket(data, 0, data.length, new InetSocketAddress(this.toIP, this.toPort));
            socket.send(packet);
            if (dataString.equals("bye")) {
               break;
            }
         } catch (IOException e) {
            e.printStackTrace();
         }
      }
      try {
         reader.close();
      } catch (IOException e) {
         e.printStackTrace();
      }
      socket.close();
   }
}
public class TalkReceive implements Runnable {
   DatagramSocket socket = null;

   public TalkReceive(int port) {
      try {
         this.socket = new DatagramSocket(port);
      } catch (SocketException e) {
         e.printStackTrace();
      }
   }

   @Override
   public void run() {
      while (true) {
         byte[] container = new byte[1024];
         DatagramPacket packet = new DatagramPacket(container, 0, container.length);
         try {
            this.socket.receive(packet); //阻塞式接收包裹
            String data = new String(packet.getData(), 0, packet.getLength());
            System.out.println(packet.getSocketAddress() + " --> " + data);
            if (data.equals("bye")) {
               break;
            }
         } catch (IOException e) {
            e.printStackTrace();
         }
      }
      socket.close();
   }
}

假设，学生和老师要聊天。

public class TalkStudent {
   public static void main(String[] args) {
      new Thread(new TalkSend("localhost", 6666, 8888)).start();
      new Thread(new TalkReceive(7777)).start();
   }
}
public class TalkTeacher {
   public static void main(String[] args) {
      new Thread(new TalkSend("localhost", 5555, 7777)).start();
      new Thread(new TalkReceive(8888)).start();
   }
}

注意端口间的对应关系即可。

URL

Uniform Resource Locator，统一资源定位器，定位资源的，定位互联网上的某一个资源。

协议://ip地址:端口：/项目名/资源

public class TestURLDemo1 {
   public static void main(String[] args) {
      try {
         URL url = new URL("http://localhost:8080/helloworld/index.jsp?key=123");
         System.out.println(url.getProtocol());
         System.out.println(url.getHost());
         System.out.println(url.getPort());
         System.out.println(url.getPath());
         System.out.println(url.getFile());
         System.out.println(url.getQuery());
      } catch (MalformedURLException e) {
         e.printStackTrace();
      }
   }
}

//使用URL下载资源
public class TestURLDemo2 {
   public static void main(String[] args) {
      try {
         URL url = new URL("https://img.lfalive.top/PT/hitpt.JPG");
         HttpURLConnection urlConnection = (HttpURLConnection) url.openConnection();
         InputStream inputStream = urlConnection.getInputStream();
         FileOutputStream fos = new FileOutputStream("download.jpg");
         byte[] buffer = new byte[1024];
         int len;
         while ((len = inputStream.read(buffer)) != -1) {
            fos.write(buffer,0, len);
         }
         fos.close();
         inputStream.close();
         urlConnection.disconnect();
      } catch (IOException e) {
         e.printStackTrace();
      }
   }
}