The IP address
IP is a unique identifier that identifies every computer on the Internet
Classification:
- IPv4:32-bit, divided into four segments (each segment ranges from 0 to 255) in decimal notation. For example: 192.168.1.1 (the number of these four segments is limited, and is not enough, Ipv6 appears)
- IPv6:128, paragraph 8, 0000 ~ FFFF hexadecimal values, colon segmentation, such as: 1080:0:0:0:8:8 00:20 0 c: 417 a
Java support for basic networking
1. To represent an IP address, the InetAddress class has two subclasses
- Inet4Address(IPv4)
- Inet6Address(IPv6)
2. Common methods (mainly understand the method of obtaining IP address objects)
- Static InetAddress getLocalHost() returns the local host
- Static InetAddress getByName(String host) Determines the IP address of the host given the host name. If an IP address exists on the LOCAL area network (LAN), an exception occurs
- Static InetAddress getByAddress(byte[] addr) getByAddress(byte[] addr) getByAddress(byte[] addr
- Boolean isReachable(int timeout) Tests whether the address can be reached (similar to ping).
Example:
public class Demo1 {
public static void main(String[] args) throws IOException {
// Obtain the local IP address
InetAddress ip1 = InetAddress.getLocalHost();
System.out.println(ip1);
// Obtain the IP address from the IP name
InetAddress ip2 = InetAddress.getByName("localhost");
System.out.println(ip2);
// Get the IP from the byte array
InetAddress ip3 = InetAddress.getByAddress(new byte[] {(byte) 10, (byte) 185, (byte) 127, (byte) 22});
System.out.println(ip3);
// Tests whether the address can be reached
System.out.println(ip1.isReachable(5000)); }}Copy the code
Results:
port
What is a port?
If an IP address is a house, a port is the door in and out of the house. A real house has only a few doors, but a single IP address can have 65536 ports (i.e. 2^16) as many! Ports are marked by port numbers, which are integers ranging from 0 to 65535 (2^16-1).
Simply put: an application on a computer is bound to a corresponding number (port), through the IP can be located to the specified host (computer), plus the port can be located to the specified program.
Note: Two programs cannot use the same port on the same machine.
URL (Uniform Resource Locator)
Uniform Resource Locator (URL) a Uniform Resource Locator (URL) that can be used to locate resources on the Internet, such as a simple web page. It consists of the following components: protocol name, host where the resource resides, port, and resource name. Such as: baidu.com: 80 / class_info /…
URLEncoder and URLDecoder
String encoding and decoding
public class Demo1 {
public static void main(String[] args) throws IOException {
/ / code
String encode = URLEncoder.encode("Progress every day!"."utf-8");
System.out.println(encode);
/ / decoding
String decode = URLDecoder.decode(encode,"utf-8"); System.out.println(decode); }}Copy the code
Results:
Differences between TCP and UDP
- Connection-based and connectionless;
- Requirements on system resources (more TCP and less UDP);
- UDP program structure is simple;
- Flow mode and datagram mode;
- TCP guarantees data correctness, UDP packet loss, TCP guarantees data order, UDP does not guarantee;
TCP protocol:
- Based on the link
- Safe and reliable
- Byte stream
- slowly
UDP protocol.
- message
- Don’t connect
- unsafe
- Speed is fast
The HTTP protocol
- Request Request object
- Request header information
- Response the corresponding object
- Information about the response header