[Java] Socket Programming network programming

Java provides network-related class libraries, painless networking, and the underlying details are handed over to the JVM control

Java implements a cross-platform network library, our development is facing a unified network programming environment

 

purpose:

Directly or indirectly communicate and communicate with other computer data through network protocols

main problem:

Accurately locate a computer or multiple computers on the network and locate specific applications on the host

How to transfer data reliably and efficiently after finding the host

 

Communication elements:

IP and port number

TCP / IP protocol

 

IP: is the unique identifier of the computer in the network

Local loopback address; 127.0.0.1 host name: LocalHost

IP address classification : IPV4 IPV6

v4-4 bytes, 4 0-255 about 4.2 billion total available, 3 billion in North America, 400 million in Asia, exhausted in 2011,

v6-128-bit 16-byte 8 unsigned integers, each integer is represented by 4 hexadecimal digits, and each number is separated by a colon

Classification by address : public address [use of the World Wide Web] and private address [use of the LAN]

192.168.0.0-192.168.255.255 is used internally by the organization

    static void socket01IP_Address() throws UnknownHostException {
        // DNS Domain Name System
        // localhost/127.0.0.1 本机地址
        InetAddress localhost = InetAddress.getByName("localhost");
        System.out.println(localhost);

        InetAddress a = InetAddress.getByName("www.cnblogs.com");
        System.out.println(a);
        // www.baidu.com/14.215.177.38
        // www.acfun.cn/117.21.225.193
        // www.bilibili.com/119.3.70.188
        // www.cnblogs.com/101.37.113.127

        InetAddress localHost = InetAddress.getLocalHost();
        System.out.println(localHost);

        String address = localHost.getHostAddress();
        String hostName = localHost.getHostName();

    }

 

The port number is the process (program) running on the computer

Different processes have different port numbers

Defined as a 16-bit integer 0-65535

Well-known ports 0-1023 Predefined service communications occupy HTTP 80, FTP 21, Telnet 23

Registration ports 1024-49151 are allocated to user processes or applications Tomcat8080, MySQL3306, Oracle1521

Dynamic port / private port 49152-65535

Socket = port number + IP address

 

TCP

-Establish a connection and form a transmission channel,

-Three-way handshake confirmation, point-to-point communication, reliable

-TCP application process client and server

-Can transfer large data

-The transmission is completed, the established connection is released, and the efficiency is low

UDP

-Data packaging, no connection

-Limit size of 64KB per package

-No response is confirmed regardless of whether the other party is prepared and whether the receiving party receives it

-Broadcast transmission

-At the end of sending, the resources are released out of order, the overhead is small and the speed is fast

 

TCP

public  class TCP_Test { 
    @Test // Server 
    public  void server () throws Exception {
         // Create server program 
        ServerSocket server = new ServerSocket (65000 ); 

        Socket client = server.accept (); // Indicates that the incoming client suite Connection 

        InputStream inputStream = client.getInputStream (); 

        byte [] bytesBuffer = new  byte [512 ]; 

        int len; 

        while ((len = inputStream.read (bytesBuffer))! = -1 ) { 
            String str= new String (bytesBuffer, 0 , len); 
            System.out.println (str); 
        } 

        System.out.println ( "Message from server: client has been received:" + client.getInetAddress (). getHostAddress () + "Message" ); 

        // Close the resource 
        inputStream.close (); 
        client.close (); 
        server.close (); 
    } 

    @Test // Client 
    public  void client () throws Exception { 

        // This is to connect The other party's socket information, IP + port 
        Socket client = new Socket (InetAddress.getByName ("localhost"), 65000 ); 

        OutputStream outputStream= client.getOutputStream (); 
        outputStream.write ( "Message sent from client: Connect Success !!!" .getBytes ()); 

        // Stream object release 
        outputStream.close (); 

        // Socket release 
        client. close (); 
    } 
}

 

UDP

public class UDP_Test {

    @Test
    public void send() throws Exception {

        DatagramSocket ds = new DatagramSocket();

        java.lang.String message = "来自发送器的消息：Hello UDP!!!";
        byte[] bytes = message.getBytes();
        InetAddress localHost = InetAddress.getLocalHost();
        DatagramPacket dp = new DatagramPacket(bytes,0,bytes.length,localHost,65000);

        // 发送包
        ds.send(dp);

        ds.close();
    }

    @Test
    public void receive() throws Exception{
        DatagramSocket ds = new DatagramSocket(65000);

        byte[] buffer = new byte[1024];
        DatagramPacket packet = new DatagramPacket(buffer,0,buffer.length);
        ds.receive(packet);

        System.out.println(new String(packet.getData(),0,packet.getLength()));

        ds.close();
    }

}

 

URL

Uniform Resource Locator Uniform Resource Locator, which represents a resource address of the network

-Is a specific URI, URL can be used to identify a resource, indicating how to locate this resource

-Transfer protocol host name port number file name fragment name? parameter list

The general port number is 80

#Clip name is the anchor point, to locate a specific part

The parameter list is a KV pair? K1 = v1 like this, if there are multiple parameters, use & connect

public  class URL_Test {
     public  static  void main (String [] args) throws Exception { 
        String url = "https://www.ygo-sem.cn/photo/story-430.aspx" ; 

        URL url_link = new URL (url) ; 

        System.out.println ( "protocol name:" + url_link.getProtocol ()); 
        System.out.println ( "host name:" + url_link.getHost ()); 
        System.out.println ( "port number:" + url_link.getPort ()); // -1 means 
        System.out.println ("file path:" + url_link.getPath ()); 
        System.out.println ( "File name:" + url_link.getFile());
        System.out.println("查询名：" + url_link.getQuery());
    }
}