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The content of this article mainly focuses on what is the basic concept of Web technology. The content of the article is clear and clear. It is very suitable for beginners to learn and is worth reading. Interested friends can follow the editor to read together. I hope you can get something through this article!

What is Web in Web development

Web is an abstract information space.

What is Web development?

Mainly refers to the development of the website, including front-end (web development) and back-end (background services).

Cpact S: client and server architecture. (software needs to be installed on the client before you can interact with the server)

Bounce S: browser, server architecture. (any application in the server can be accessed through the browser)

Technologies needed for Web development

Front end: html (Hypertext markup language), css (cascading style sheets), JavaScript (dynamic scripting language), jQuery (js Framework), vueJS (Library) and so on.

Backend: JSP (Servlet) and so on.

II. Server pilot concept

Static pages: actual web pages, standard HTML documents, loaded (displayed) directly to the client browser without being compiled by the server. The suffix name can be .html, .htm, and so on.

Language used: html

Advantages: there is a fixed URL; saved on the server; separate design; targeted; stable; access speed is faster than dynamic pages; no database support; easy to be searched by search engines.

Disadvantages: heavy workload of production and maintenance; poor interaction; difficulties in information data retrieval and maintenance (without database support).

Dynamic pages: the content of the page varies from person to person. In addition to static HTML code, it also contains server code that can only be parsed on the server side. The suffix name can be .aspx, .jsp, .php, and so on.

Languages used: html + ASP, PHP, JSP

Advantages: good interactivity; vary from person to person; database support; easy maintenance

Disadvantages: slow access speed; difficult to be retrieved by search engines; complex design (database support).

Note: the concept of dynamic page corresponds to that of static page, and the dynamic meaning does not represent the dynamic effect of the page.

The main differences between static pages and dynamic pages

Whether to run the program on the server. The programs and pages running on the client side are static; the programs and pages running on the server side are dynamic, and they will return different pages according to the business logic with different customers and different times.

Server

A server is a device that provides computing services.

Simply put, it is a more advanced computer. Our computer is the client that sends the request, while the server is the server that accepts the request and responds and gives feedback in a timely manner.

After the Web project is developed, it needs to be published (deployed) to a server before it can be accessed by the outside world.

Web server

The Web server is designed to provide HTTP content (Internet access service), which can only send the content of static pages.

Mainstream Web server: Apache.

Web application server

First, the Web application server can do whatever the Web server can do, so the Web application server can act as a Web server. In addition, the Web server can provide dynamic content. It can provide the function of business logic processing for the program through many protocols.

Third, Web service process Web service architecture

The above is a diagram of the Web service architecture.

It can be divided into three layers: presentation layer, business layer, persistence layer (data access layer).

Presentation layer: presentation of user interaction interface and user operation interface

Business layer: to realize the logical business that interacts with users, which is the core of the whole system.

Persistence layer: the operation relative to the database or file to achieve the persistent preservation of object data.

Web service process (browser as client)

1) the user makes an action. It can be to fill in the URL and hit enter, or it can be to click on a hyperlink. The browser gets the event at this point.

2) the browser establishes a TCP connection with the server program and sends a HTTP request (the browser packages the user's events according to the HTTP protocol and pushes them into the server corresponding program).

3) the server program receives the request from the browser and parses it with HTTP protocol to understand the customer's intention. At this point, the server interacts with the database to find out whether there are any requested resources.

If the file exists, the server sends a HTTP response to the browser, packages the resource in HTTP protocol format, and returns the resource; if it does not exist, it returns an error message that the resource cannot be found.

4) the browser receives the response and parses the packet in HTTP protocol format. If the response file contains images, styles, etc., the browser will repeat the above action again.

5) parsing files (which can be .html, .gif, etc.) are displayed in the browser interface.

IV. Other basic concepts in Web: client and server

Client: also known as the client. To provide local services to customers, it needs to run with the server. In Web, it exists as a request object.

Server: provide customers with information resources and information services. In Web, it exists as a response object.

In general Web services, the client sends out the HTTP request, and then the corresponding server sends the HTTP response to return the data and other data information requested by the client.

IP address and port number

IP protocol: a protocol (rules) designed for computer networks to connect and communicate with each other.

IP address: a unified address format provided by the IP protocol that assigns a logical address to each host.

Local IP address: 127.0.0.1

IP address types: public address and private address.

Class A: 10.0.0.0 ~ 10.255.255.255

Category B: 172.16.0.0 ~ 172.31.255.255

Class C: 192.168.0.0 ~ 192. 168.255.255

Port: virtual port, which refers to a port inside a computer or within a switch router.

Port number: a concept similar to a house number. The client can find the corresponding server through the IP address, and each service application corresponds to a port number. Only through the port number can the client really access the server. Its range is 0 ~ 65535.

For example: the 80 port number of the web browsing service.

URL

URL: uniform resource locator. On www, each information resource has a unified and unique address, namely URL.

The composition of URL: protocol, hostname, port number, relative path.

Layering of computer network

The computer network system is formed by independent computers connected by existing communication systems, and its function is to realize remote access and resource sharing of computers. Therefore, the problem of computer network is mainly to solve how to achieve correct and reliable communication between computers working independently in different places. The computer network hierarchical architecture model is designed to solve this key problem of computer network.

The principle of hierarchical division: functional division, isolation and stability, branch expansion, convenient implementation.

From the point of view of the principle of network communication, the computer network is divided into five layers: application layer, transport layer, network layer, data connection layer and physical layer. As shown in the figure, the more you go up, the closer you get to the user, and the lower you get closer to the bottom of the computer.

Physical layer: connect physical computers with optical fibers, cables, etc., and transmit electrical signals such as the original binary 0Phon1 between computers.

Data connection layer: above the physical layer, the transmission rules are specified for 0Magne1, and both the sender and the interviewee communicate according to the rules.

Ethernet protocol, MAC address, broadcast and ARP protocol.

Network layer: responsible for providing communication services for different hosts on the packet switching network, which is host-to-host communication.

IP protocol, ARP protocol, subnet mask, DNS server.

Transport layer: the network layer is only responsible for transferring data to the host, but not to the process. The transport layer is responsible for the transmission between the process and the host. Is port-to-port communication.

UDP protocol, TCP protocol.

Application layer: provide corresponding services for some applications.

HTTP protocol and so on.

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