Http protocol and Tomcat server for Java learning

HTTP protocol

HTTP, HyperText Transfer Protocol (HyperText Transfer Protocol) is the most widely used network protocol on the Internet. All www files must comply with this standard. HTTP was originally designed to provide a way to publish and receive HTML pages

The composition of the Http protocol

Http protocol consists of Http request and Http response . When you enter a URL in the browser to visit a website, your browser will encapsulate your request into an Http request and send it to the server site. After the server receives the request, it will organize the response The data is encapsulated into an Http response and returned to the browser, that is, there is no response without a request

HTTP request

Edit a form page of form.html as follows:

Click the submit button to capture the package as follows:

1) Request line

Request method: POST, GET

Request resource: /DemoEE/form.html

Protocol version: HTTP/1.1

HTTP/1.0, send a request, create a connection, get a web resource, disconnect

HTTP/1.1, send a request, create a connection, get multiple web resources, keep the connection

2) Request header

Some information sent by the client to the server in the request header, using a key-value pair to represent key:value

Common request headers	Description (red master, other understand)
Referer	The browser informs the server where the current request is coming from. If it is direct access, this header will not be present. Commonly used for: anti-theft chain
If-Modified-Since	The browser notifies the server of the last change time of the local cache. Combined with another response header controls the caching of browser pages.
Cookie	Session-related technologies used to store cookie information cached by browsers.
User-Agent	The browser notifies the server, the client browser and operating system related information
Connection	Stay connected. Keep-Alive connection, close has been closed
Host	The requested server hostname
Content-Length	the length of the request body
Content-Type	If it is a POST request, there will be this header. The default value is application/x-www-form-urlencoded, indicating that the content of the request body is url encoded
Accept：	The MIME types supported by the browser. A way of describing a file type. MIME format: big type/small type[;parameters] E.g: text / html, html text text/css, css files text/javascript, js files image/*, all image files
Accept-Encoding	The browser informs the server of the data compression formats supported by the browser. Such as: GZIP compression
Accept-Language	The browser informs the server of the languages supported by the browser. Various languages (internationalized i18n)

3) Request body

When the request method is post, the request body has the requested parameters in the following format:

username=zhangsan&password=123

When the request method is get, the request parameters will not appear in the request body, but will be spliced after the url address

http://localhost:8080...?username=zhangsan&password=123

Http response

1) Response line

HTTP protocol

status code:

200: The request was successful

302: Request redirection

304: The requested resource has not changed, access the local cache

404: The requested resource does not exist, usually the user path is written incorrectly, or the server-side resource may be deleted

500: Internal server error, usually the program throws an exception.

Status information: Status information changes according to the status code change

2) Response header

The responses are also in the form of key-value pairs, and the server returns the information to the client in the form of key-value pairs

Common request headers	describe
Location	Specifies the path of the response, which needs to be used in conjunction with the status code 302 to complete the jump.
Content-Type	Type of response body (MIME type) Value: text/html;charset=UTF-8
Content-Disposition	Parse the body in download mode via browser 取值：attachment;filename=xx.zip
Set-Cookie	与会话相关技术。服务器向浏览器写入cookie
Content-Encoding	服务器使用的压缩格式取值：gzip
Content-length	响应正文的长度
Refresh	定时刷新，格式：秒数;url=路径。url可省略，默认值为当前页。取值：3;url=www.itcast.cn //三秒刷新页面到www.itcast.cn
Server	指的是服务器名称，默认值：Apache-Coyote/1.1。可以通过conf/server.xml配置进行修改。<Connector port="8080" ... server="itcast"/>
Last-Modified	服务器通知浏览器，文件的最后修改时间。与If-Modified-Since一起使用。