20165212 ninth week study summary

20165212 ninth week study summary

Textbook content summary

URL class

• The URL class is an important class in the java.net package
• A URL object contains three basic information: protocol, address and resource
  • Protocol: must be a protocol supported by the Java virtual machine where the URL object is located, commonly used: Http, Ftp, File protocols, specified by the parameter protocol
  • Address: must be a valid IP address or domain name that can be connected, specified by the parameter host
  • Resource: can be any file on the host, specified by the parameter file
• Construction method
  • public URL (String spec) throws MalformedURLException
  • public URL(String protocol,String host,String file) throws MalformedURLException
• Call the InputStream openStream() method to return an input stream
  • InetAddress class
• Two ways for hosts on the Internet to represent addresses
  • domain name
  • IP address
• get address
  • Get the host address on the Internet: getByName(String s)
  • Get the local machine address: getLocalHost()

- socket

• It is a network communication based on the TCP protocol
• client socket
  • Object creation method: use the Socket class
  • Socket construction method: Socket(String host,int port)
• ServerSocket objects and server-side sockets
  • Constructor: ServerSocket(int port)
• Use the method accept() to connect the client's socket with the server's socket
  • try{ Socket sc = serverForClient.accept(); } catch(IOException e) {}
• After the communication is completed, the socket uses the close() method to close the socket connection
• multithreading technology
  • When the server receives a client's socket, it starts a thread dedicated to serving the client
• Basic Principles of Socket Communication
  • The server should start a dedicated thread in which the connection to the client's socket is established
  • Since the input stream of the socket may block when reading information, both the client and the server need to read the information in a separate thread
• UPD datagram
  • Basic mode of communication based on UPD
  • Pack the data and send it to the destination
  • Receive incoming packets and view content
• send packets
  • 打包：使用DatagramPacket类 DatagramPacket(byte data[],int length,InetAddtress address,int port) DatagramPack(byte data[],int offset,int length,InetAddtress address,int port)
• Send: Create an object using the constructor DatagramSocket()
• receive packets
  • Create an object using the constructor DatagramSocket(int port)
  • Use the method receive(DatagramPacket pack) to receive data packets
• broadcast datagram
  • Class A address: a<128, then bcd represents the host
  • Class B address: 128<=a<192, then ab represents the network address, and cd represents the host address
  • Class C address: a>=192, abc represents the network address, d represents the host address
  • Class D addresses: 224.0.0.0~224.255.255.255 are reserved addresses
• Hosts that want to broadcast or receive broadcasts must be joined to the same class D address
  • RMI is a distributed technology that allows an application on one virtual machine (JVM) to request a method call on an object located on another JVM on the network

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Code cloud link: https://gitee.com/BESTI-IS-JAVA-2018/20165212RenYin/tree/master/20165212/%E7%AC%AC13%E7%AB%A0

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