The definition and difference between cookie and session

Definition of both:

When you browse a website, the WEB server will first send a small amount of information to your computer, and the cookie will help you type the text or text on the website. These are some choices,

are all recorded. The next time you visit the same website, the WEB server will first check to see if there is any cookie information it left last time. If so, it will judge the user based on the content in Cookie

and send a specific message. web content for you. The use of cookies is very common. Many websites that provide personalized services use Cookie

to identify users so as to send user-tailored content, such as free email websites with Web interfaces. All use cookies.

Specifically, the cookie mechanism uses a solution that maintains state on the client side, while the session mechanism uses a solution that maintains state on the server side.

At the same time, we also see that since the solution of maintaining state on the server side also needs to save an identity on the client side, the session mechanism may need to use the cookie mechanism

to achieve the purpose of saving the identity. , but it actually has other options.

Cookie mechanism. Orthodox cookie distribution is achieved by extending the HTTP protocol. The server adds a special line of instructions to the HTTP response header to prompt the browser to generate the corresponding cookie according to the instructions. However, pure client-side scripts such as JavaScript or VBScript can also generate cookies. The use of cookies is automatically sent to the server by the browser in the background according to certain principles. The browser checks all stored cookies. If the scope

declared by a cookie is greater than or equal to the location of the resource to be requested, the cookie is attached to the HTTP request header of the requested resource and sent to the server.

The content of cookie mainly includes: name, value, expiration time, path and domain. The path and domain together form the scope of the cookie. If the expiration time is not set, it means that the lifetime of these

cookies is during the browser session. When the browser window is closed, the cookie will disappear. This type of cookie that lasts for the duration of the browser session is called a session cookie.

Session cookies are generally not stored on the hard disk but in memory. Of course, this behavior is not regulated by the specification. If an expiration time is set, the browser will save the cookie

to the hard disk. If you close and open the browser again, these cookies will still be valid until the set expiration time is exceeded. Cookies stored on the hard disk can be shared between different browser processes, such as two IE windows. For cookies stored in memory, different browsers have different processing methods

session mechanisms. The session mechanism is a server-side mechanism. The server uses a structure similar to a hash table (or may use a hash table) to save information.

When the program needs to create a session for a client's request, the server first checks whether the client's request already contains a session identifier

(called session id). If so, Contains indicates that a session has been created for this client before, and the server will retrieve this session according to the session id

(if it cannot be retrieved, a new one will be created). If the client request does not contain the session id, then For this purpose, the client creates a session and generates a session id associated with this session. The value of the session id should be a string that is neither repeated nor easy to find patterns to counterfeit. This The session id will be returned to the client in this response

for storage. The method of saving this session id can use cookies, so that during the interaction process, the browser can automatically send this identifier to the

server according to the rules. Generally, the name of this cookie is similar to SEEESIONID. But cookies can be artificially disabled, and there must be other mechanisms so that when cookies are disabled, the session id can still be passed back to the server.

A frequently used technique is called URL rewriting, which is to append the session id directly to the end of the URL path. There is also a technique called form hidden fields. That is, the server

will automatically modify the form and add a hidden field so that the session id can be passed back to the server when the form is submitted. For example:

In fact, this technique can be simply replaced by applying URL rewriting to the action.

The difference between cookies and sessions:

1. Cookie data is stored on the client's browser, and session data is placed on the server.

2. Cookies are not very safe. Others can analyze the COOKIE stored locally and conduct COOKIE deception
Considering security, session should be used.

3. The session will be saved on the server within a certain period of time. When access increases, it will take up more of your server's performance
Considering reducing server performance, COOKIE should be used.

4. The data saved by a single cookie cannot exceed 4K. Many browsers limit a site to save up to 20 cookies.

5. So personal suggestion:
Store important information such as login information as SESSION
If other information needs to be retained, it can be placed in COOKIE

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