Overview of network programming

1. How to realize the communication between hosts in the network

   • Address of both parties
     • IP
     • Port number
   • Certain rules

     • OSI reference model: the model is too idealized to be widely popularized on the Internet

     • TCP/IP reference model (or TCP/IP Protocol): a de facto international standard.

IP

• IP address: InetAddress

  • Uniquely identifies the computer (communication entity) on the Internet

  • Local loopback address: 127.0.0.1 hostname: localhost

  • IP address classification method 1: IPV4 and IPV6

    • IPV4: 4 bytes, 4 0-255. About 4.2 billion and 3 billion are in North America and 400 million in Asia. It was exhausted in early 2011. Expressed in dotted decimal system, such as 192.168.0.1
    • IPV6: 128 bits (16 bytes), written as 8 unsigned integers. Each integer is represented by four hexadecimal bits, separated by colons (:), such as 3ffe:3201:1401:1280:c8ff:fe4d:db39:1984

  • IP address classification method 2: public address * * (for World Wide Web use) and private address (for LAN use) * *. 192.168. At the beginning is the private address. The range is 192.168.0.0 – 192.168.255.255, which is specially used within the organization

  • Features: not easy to remember

• How to instantiate InetAddress: two methods: getByName(String host) getLocalHost();

Two common methods: getHostName()/getHostAddress()

Port number

• The port number identifies the process (program) running on the computer
• Different processes have different port numbers
• It is specified as a 16 bit integer 0 ~ 65535.
• Port classification:
  • **Recognized port: * * 0 ~ 1023. Occupied by predefined service communication (e.g. HTTP occupies port 80, FTP occupies port 21, Telnet occupies port 23)
  • **Registration port: * * 1024 ~ 49151. Assigned to a user process or application. (for example, Tomcat occupies port 8080, MySQL occupies port 3306, Oracle occupies port 1521, etc.).
  • Dynamic * * / private port: * * 49152 ~ 65535**
• The combination of port number and IP address yields a network Socket: Socket * *.

TCP/IP protocol cluster

• Before using TCP protocol, a TCP connection must be established to form a data transmission channel

• Before transmission, the "three-time handshake" mode is adopted for point-to-point communication, which is reliable

• Two application processes that communicate with TCP protocol: client and server.

• A large amount of data can be transmitted in the connection

• After transmission, the established connection needs to be released, which is inefficient

• @Test
  public void client(){
      OutputStream outputStream=null;
      Socket socket=null;
      try {
          //1. Create a Socket object to indicate IP and port number
          InetAddress inetAddress=InetAddress.getByName("127.0.0.1");
          socket=new Socket(inetAddress,8866);
  
          //2. Obtain an output stream for outputting data
          outputStream=socket.getOutputStream();
          //3. Write operation
          outputStream.write("Zhang Haohui studies java".getBytes());
      } catch (IOException e) {
          e.printStackTrace();
      } finally {
          //4. Close resources
          if(socket!=null){
              try {
                  socket.close();
              } catch (IOException e) {
                  e.printStackTrace();
              }
          }
          if(outputStream!=null){
              try {
                  outputStream.close();
              } catch (IOException e) {
                  e.printStackTrace();
              }
          }
      }
  
  
  }
  
  //Server
  @Test
  public void server(){
      InputStream inputStream= null;
      ByteArrayOutputStream bytes= null;
      Socket socket1=null;
      ServerSocket socket=null;
      try {
          //1. Define a ServerSocket object storage port
          socket=new ServerSocket(8866);
          //2. Create a Socket object with the port number of the ServerSocket object
          socket1=socket.accept();
          //3. Create input stream
          inputStream = socket1.getInputStream();
          //4. Conversion flow
          bytes = new ByteArrayOutputStream();
          byte[] bytes1 = new byte[20];
  
          int len;
          while((len=inputStream.read(bytes1))!=-1){
              bytes.write(bytes1,0,len);
          }
  
          System.out.println(bytes.toString());
      } catch (IOException e) {
          e.printStackTrace();
      } finally {
          //5. Close the flow
          if(bytes!=null){
              try {
                  bytes.close();
              } catch (IOException e) {
                  e.printStackTrace();
              }
          }
          if(inputStream!=null){
              try {
                  inputStream.close();
              } catch (IOException e) {
                  e.printStackTrace();
              }
          }
          if(socket!=null){
              try {
                  socket.close();
              } catch (IOException e) {
                  e.printStackTrace();
              }
          }
          if(socket1!=null){
              try {
                  socket1.close();
              } catch (IOException e) {
                  e.printStackTrace();
              }
          }
      }
  }
  

• @Test
  public void client(){
      Socket socket=null;
      OutputStream outputStream=null;
      FileInputStream fileInputStream=null;
      try {
          socket=new Socket(InetAddress.getByName("127.0.0.1"),8888);
          outputStream=socket.getOutputStream();
          fileInputStream=new FileInputStream("zjm.jpg");
  
          byte[] bytes=new byte[1024];
          int len;
          while((len=fileInputStream.read(bytes))!=-1){
              outputStream.write(bytes,0,len);
          }
      } catch (IOException e) {
          e.printStackTrace();
      } finally {
          if(fileInputStream!=null){
              try {
                  fileInputStream.close();
              } catch (IOException e) {
                  e.printStackTrace();
              }
          }
          if(outputStream!=null){
              try {
                  outputStream.close();
              } catch (IOException e) {
                  e.printStackTrace();
              }
          }
          if(socket!=null){
              try {
                  socket.close();
              } catch (IOException e) {
                  e.printStackTrace();
              }
          }
      }
  }
  
  @Test
  public void server(){
      Socket socket=null;
      InputStream inputStream=null;
      FileOutputStream file=null;
  
      try {
          socket=new ServerSocket(8888).accept();
          file=new FileOutputStream("zjm3.jpg");
          inputStream=socket.getInputStream();
          byte[] bytes=new byte[1024];
          int len;
          while((len=inputStream.read(bytes))!=-1){
              file.write(bytes,0,len);
          }
      } catch (IOException e) {
          e.printStackTrace();
      } finally {
          if(file!=null){
              try {
                  file.close();
              } catch (IOException e) {
                  e.printStackTrace();
              }
          }
          if(inputStream!=null){
              try {
                  inputStream.close();
              } catch (IOException e) {
                  e.printStackTrace();
              }
          }
          if(socket!=null){
              try {
                  socket.close();
              } catch (IOException e) {
                  e.printStackTrace();
              }
          }
      }
  }
  

UDP/IP protocol cluster

• Encapsulate the data, source and destination into data packets without establishing a connection

• The size of each datagram is limited to 64K

• Whether the sending party is ready or not, the receiving party does not confirm the receipt, so it is unreliable

• Can broadcast and send

• At the end of sending data, there is no need to release resources, low overhead and high speed

• technological process:

  1. Datagram socket and datagram packet
  2. Establish sender and receiver
  3. Create packet
  4. Call Socket sending and receiving methods
  5. Close Socket

• The sender and receiver are two independent running programs

• @Test
      public void send(){
          DatagramSocket socket =null;
          try {
              socket = new DatagramSocket();
              String str="Zhang Haohui, come on today";
              byte[] bytes=str.getBytes();
              InetAddress inet=InetAddress.getLocalHost();
              DatagramPacket packet = new DatagramPacket(bytes,bytes.length,inet,8888);
              socket.send(packet);
              socket.close();
          } catch (IOException e) {
              e.printStackTrace();
          } finally {
              if(socket!=null){
                  try {
                      socket.close();
                  } catch (Exception e) {
                      e.printStackTrace();
                  }
              }
          }
      }
  
      @Test
      public void accept(){
  
          DatagramSocket socket =null;
          DatagramPacket packet =null;
          try {
              socket = new DatagramSocket(8888);
  
              byte[] bytes=new byte[10];
              packet = new DatagramPacket(bytes,0,bytes.length);
              socket.receive(packet);
              FileOutputStream file=new FileOutputStream("hello.txt");
              file.write(packet.getData(),0, packet.getLength());
  
              System.out.println(new String(packet.getData(),0,packet.getLength()));
          } catch (IOException e) {
              e.printStackTrace();
          } finally {
              if(socket!=null){
                  try {
                      socket.close();
                  } catch (Exception e) {
                      e.printStackTrace();
                  }
              }
          }
      }
  

URL programming

1. URL: uniform resource locator, corresponding to a resource address on the Internet
2. Format: Protocol hostname port number resource address parameter list
3. Common methods:
   • public String getProtocol() gets the protocol name of the URL
   • public String getHost() gets the host name of the URL
   • public String getPort() gets the port number of the URL
   • public String getPath() gets the file path of the URL
   • public String getFile() gets the file name of the URL
   • public String getQuery() gets the query name of the URL