Talking about the difference between get and post in HTTP

HTTP defines different ways to interact with the server, with 4 basic methods, namely get,post,put,delete. URL full name is a resource descriptor, we can think: a URL address, which is used to describe a network of resources, and HTTP get,post,put,delete corresponding to this resource, change, increase, delete 4 operations. Here, you should have a general understanding, get is generally used to get/query resource information, and post is generally used to update resource information.

　　1. According to the HTTP specification, get is used for information acquisition and should be secure and idempotent.

(1). So-called security means that the operation is used to obtain information rather than modify information. In other words, GET requests generally should not have side effects. That is, it simply gets the resource information, just like a database query, without modification, adding data without affecting the state of the resource.

* Note: The meaning of security here is simply non-modification information.

(2). Idempotent means that multiple requests to the same URL should return the same result. Here I'll explain the concept of idempotent :

　　 Power, etc.(Idempotent, Idempotence) is a mathematical or computer concept, common in abstract algebra.
Idempotent has several definitions:
For the monocular operation, if an operation has the same result as the result of doing the operation more than once in the range of a number of times, then we call the Operation Idempotent. For example, the absolute value operation is an example, in the real number set, there is abs (a) =abs (ABS (a)).
For binocular operations, it is required that when the two values of the participating operations are equal, if the results of the operation are equivalent to the two values of the participating operations, the exponentiation of the operation, such as a function of the maximum value of two numbers, is in the power of the real concentration, that is, max (x,x) = x.

After reading the above explanations, you should be able to understand the meaning of get idempotent.

But in practical applications, the above 2 rules are not so strict. Cite examples of other people's articles: for example, the front page of news sites is constantly being updated. Although the second request returns a different batch of news, the operation is still considered safe and idempotent, as it always returns the current news. Fundamentally, if the goal is that when a user opens a link, he can be confident that the resource is not changed from its point of view.

　　2. According to the HTTP specification, post represents a request that may modify resources on the server. Continue to cite the example above: or the news to the website as an example, readers of the news to publish their own comments should be done through post, because after the comments submitted site resources have been different, or that the resources have been modified.

It probably says something about the original reason for Get and post in the HTTP specification. But in the actual time, many people do not follow the HTTP specification to do, the cause of this problem is many, for example, say:

　　1. Many people are greedy and use get when updating resources, because the post must go to the form (form), which can be a bit troublesome.

　　2. The increase of resources, delete, change, check operation, in fact, can be completed through get/post, do not need to use put and delete.

　　3. Another is that the early web MVC framework designers did not consciously view and design URLs as abstract resources, so a more serious problem is that the traditional web MVC framework basically only supports get and post two HTTP methods, The put and delete methods are not supported.

* Simply explain that MVC:MVC is originally present in the desktop program, m refers to the data model, v refers to the user interface, and C is the controller. The purpose of using MVC is to separate the implementation code for M and v so that the same program can use a different representation.

The above 3 points typically describe the style of the stereotype (no strict adherence to the HTTP specification), with the development of the architecture, there is now rest (representational state Transfer), a set of new styles to support the HTTP specification, here is not much to say, you can refer to the RESTful Web Services.

After talking about the original reason, let's look at the difference between the get and post from the surface as above:

　　1. The data for the GET request is appended to the URL (that is, the data is placed in the HTTP protocol header), to split the URL and transfer the data, and the parameters are connected &, for example: Login.action?name=hyddd&password=idontknow &VERIFY=%E4%BD%A0%E5%A5%BD. If the data is an English letter/number, sent as is, if it is a space, converted to +, if it is Chinese/other characters, the string is directly encrypted with BASE64, such as:%E4%BD%A0%E5%A5%BD, where the xx in%xx is the symbol in 16 binary notation ASCII.

Post submits the data to the packet in the HTTP packet.

　　2. " The data submitted by the Get method can only be 1024 bytes, in theory post has no limit, can transmit a large amount of data, IIS4 in the maximum of 80kb,iis5 100KB "??!

The above sentence I transferred from other articles, in fact, this is wrong, inaccurate:

(1). First, "The data submitted by the Get method can only be 1024 bytes," Because get is the data submitted through a URL, then the amount of data that get can commit is directly related to the length of the URL. In fact, the URL does not have the upper limit of the argument, the HTTP protocol specification does not limit the length of the URL. This restriction is restricted to specific browsers and servers. IE's limit on URL length is 2083 bytes (2k+35). For other browsers, such as Netscape, Firefox, etc., there is theoretically no length limit, and its limitations depend on the support of the operating system.

Note that this is the limit for the entire URL length, not just your parameter value data length. [see reference 5]

(2). In theory, the post is no size limit, the HTTP protocol specification is not a size limit, said "post data volume exists 80k/100k size limit" is inaccurate, post data is not limited, the limit is the processing capacity of the server handler.

For ASP programs, the request object has a 100K data length limit when processing each form field. However, if you use Request.BinaryRead, you do not have this limitation.

By this extension, for IIS 6.0, Microsoft has increased its restrictions for security reasons. We also need to note:

1). IIS 6.0 default ASP post data is up to 200KB, and each form field limit is 100KB.
2). The maximum size of the IIS 6.0 default upload file is 4MB.
3). The default maximum request header for IIS 6.0 is 16KB.
These restrictions do not precede IIS 6.0. [see reference 5]

So the above 80k,100k may just be the default value (note: I have not confirmed the parameters of IIS4 and IIS5), but I am sure I can set it myself. Because each version of IIS does not have the same default values for these parameters, refer to the relevant IIS configuration documentation.

　　3. In ASP, the server obtains the GET request parameter with Request.QueryString, obtains the POST request parameter with the Request.Form. In JSP, with Request.getparameter (\ "xxxx\") to obtain, although JSP also has the request.getquerystring () method, but the use of more trouble, such as: Pass a test.jsp?name= HYDDD&PASSWORD=HYDDD, with Request.getquerystring () is: name=hyddd&password=hyddd. In PHP, you can use $_get and $_post to get the data in the get and post separately, while $_request can get the data from the get and post two requests. It should be noted that the use of JSP in the request and PHP use $_request will have hidden trouble, this next time to write an article summary.

　　4. The security of post is higher than the security of get. Note: The security described here is not the same concept as the "security" mentioned in get above. The meaning of "security" above is simply not to make data changes, and the meaning of security here is the meaning of true security, such as: submit data through get, user name and password will appear in plaintext on the URL, because (1) the login page may be cached by the browser, (2) Other people to view the browser's history, Then other people can get your account number and password, in addition, using get to submit data may also cause Cross-site request forgery attack.

To summarize, get is a request to send data to the server, and post is a request to submit data to the server, in form (form), the method defaults to "get", in essence, get and post just send mechanism is different, not one to take a hair!

Two methods of HTTP request: GET and POST

In the request-response between the client and the server, the two most commonly used methods are: GET and POST.

• GET-Requests data from the specified resource.
• POST-submits the data to be processed to the specified resource

GET method

Note that the query string (name/value pair) is sent in the URL of the GET request:

/test/demo_form.asp?name1=value1&name2=value2

Some additional comments about the GET request:

• Get requests can be cached
• GET requests remain in browser history
• Get requests can be bookmark-Favorites
• GET requests should not be used when handling sensitive data
• Get request has a length limit
• GET requests should only be used to retrieve data

POST method

Note that the query string (name/value pair) is sent in the HTTP message body of the POST request:

Post/test/demo_form.asp http/1.1host:w3schools.comname1=value1&name2=value2

Some additional comments about the POST request:

• POST requests are not cached
• POST requests are not persisted in browser history
• POST cannot be bookmarked
• POST request has no requirement for data length

Compare GET to POST

The following table compares the two HTTP methods: GET and POST.

	GET	POST
Back button/refresh	harmless	data will be re-mentioned (The browser should inform the user that the data will be resubmitted).
bookmarks	bookmark bookmarks	cannot be bookmarked
cache	can be cached	cannot be slowed Save
encoding type	application/x-www-form-urlencoded	application/x-www-form-urlencoded or Multipart/form-data. Use multiple encodings for binary data. The
history	parameter remains in the browser history. The	parameter is not saved in the browser history.
Restrictions on the length of data	Yes. When data is sent, the GET method adds data to the URL, and the length of the URL is limited (the maximum length of the URL is 2048 characters).	is unrestricted.
restrictions on data types	allow only ASCII characters. There is no limit to	. Binary data is also allowed.
security	GET is less secure than POST because the data sent is part of the URL. Never use GET when sending passwords or other sensitive information!	POST is more secure than GET because parameters are not saved in the browser history or Web server logs.
Visibility	data is visible to everyone in the URL. The	data is not displayed in the URL.

Other HTTP Request Methods

Some other HTTP request methods are listed in the following table:

Method	Description
HEAD	Same as GET, but returns only the HTTP header and does not return the document body.
PUT	Uploads the specified URI representation.
DELETE	Deletes the specified resource.
OPTIONS	Returns the HTTP methods supported by the server.
CONNECT	Convert the request connection to a transparent TCP/IP channel.

Talking about the difference between get and post in HTTP