http
Introductionhttp
The request part of http
Basic structure of requestRequest lineDetailed explanation
HTTP request headerHttp
Response detailshttp
Basic structure of responseStatus linehttp
Detailed explanation of response message headerExpires, Pragma, Cache-Control
Set not to cacheExpires, Pragma, Cache-Control
Settings Specify cache timeHTTP
Request details——General information header
http introduction
http protocol is based on tcp/ip protocol
http protocol full name Hypertext Transfer Protocol ( HTTP,HyperText Transfer Protocol)
http protocol version 1.0 1.1 2.0
http 1.0 becomes a short connection, http 1.1 is called a long connection
The so-called long and short refers to the long connection lasting 1.1 30s and the short connection being disconnected immediately after sending the data
Http defines different methods for interacting with the server. There are four basic methods, namely GET, POST, PUT, and DELETE. The full name of URL is resource descriptor. We can think of it this way: a URL address, which is used to describe a resource on the network, and GET, POST, PUT, and DELETE in HTTP correspond to the search and modification of this resource. Add and delete 4 operations. At this point, everyone should have a general understanding. GET is generally used to obtain/query resource information, while POST is generally used to update resource information.
#The request part of http
Basic structure of http request
Request line
Message header
A blank line
## Content
Request line
Request methods include: post, get, options, delete, trace, put
Commonly used ones are: post, get
The difference between post and get:
GET uses URL or Cookie to pass parameters. And POST puts the data in BODY.
The GET URL will have a length limit, and the POST data can be very large.
POST is safer than GET because the data is not visible on the address bar.
Detailed explanation of HTTP request headers
Accept: Tell the server the files I can accept Type MIME types acceptable to the browser
Accept-Charset: Character set encoding acceptable to the browser
Accept-Encoding: Can accept compressed data in a certain format such as: gzip, compress. The data encoding method that the browser can decode
Accept-Langage: The language supported by the browser
Host: Indicates who the host I am looking for is
## If-Wodified-Since: Tell the server whether there is a file to be requested in the local cache that contains the time of the requested file // The server receives this request and compares the time to determine whether the file requested by the browser has changed. If Changes will send a new file to the browser. The data will not be sent again without changes. //Note: It will only be returned if the requested content has been modified after the specified date, otherwise 304"Not will be returned.
Modified" response.
Referer: Tell the server where I am from. This message header is often used to prevent hot links.My personal understanding on how to prevent hotlinking:
Hotlinking: Hotlinking means that the service provider itself does not provide services Content, bypassing other beneficial end-user interfaces (such as advertisements) through technical means, directly providing service content of other service providers to end-users on their own websites, defrauding end-users’ browsing and click-through rates. No beneficiaries. Providing resources or providing few resources without any benefit to the real service provider
## The value of the referer is what you click on the connection file. Location. referer.startWith("Internal Path");
#Cookie: This is the most important request header information. One
##Connection: Indicates whether a persistent connection is required. If the Servlet sees that the value here is "Keep-Alive", or see Since the request uses HTTP 1.1 (HTTP 1.1 uses persistent connections by default), it can take advantage of persistent connections and significantly reduce the download time when the page contains multiple elements (such as Applets, images). At this point, the Servlet needs to send a Content-Length header in the response. The simplest way to implement it is: first write the content
ByteArrayOutputStream and then calculates its size before actually writing out the contents.
Date: The time when the browser sent the http request.
Content-Length: Indicates the length of the request message body.
##UA-Pixels, UA-Color, UA-OS, UA-CPU: Sent by some versions of IE browser Non-standard request headers indicating screen size, color depth, operating system and CPU type.
Http response details
The basic structure of http response
## Status line
Multiple headers
One blank line
Entity content
##Status line
Format: http version number status code reason description
# Example : HTTP/1.1 200 OK
The status code is used to indicate the server's processing result of the request. It is a three-dimensional decimal number. Response status codes are divided into 5 categories.
Status code
##Meaning
100~199
indicates that the request was successfully received and the client is required to continue submitting. The entire processing process can be completed only with the next request
200~299
indicates that the request was successfully received and the entire processing process has been completed. Commonly used 200
##300~399
## is used to complete the request , the client needs to further refine the request, for example: the requested resource has been moved to a new address, commonly used 302, 307
##400~ 499
The client's request is incorrect. Commonly used 404
##500~599
## appears on the server side Error, commonly used 500
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