GET and POST are two commonly used request methods in the HTTP protocol, mainly used for data transmission between clients and servers. They are often asked about in interviews. Here is a detailed introduction to the differences between Get and Post.
- There is no essential difference between Get and Post
First of all, there is no essential difference between Get and Post. Most web frameworks (such as Spring and Django) allow developers to customize the processing logic of request methods. Even if the method does not conform to the semantics, the server can still correctly parse the data.
- Semantic differences
- GET: It is originally designed to obtain resources, generally used to request specific data from the server, such as accessing web pages, obtaining pictures, etc. The client passes parameters through the URL to obtain the corresponding resources.
- POST: It is mainly used to submit data to the server, usually for creating and updating resources, such as submitting forms, uploading files and other operations. The client sends data in the request body to the server.
In general, Get is to obtain resources from the server, while Post is to submit resources to the server.
- Ways of carrying data
Get:
- Data location: Data is passed through the query string in the URL, in the format of key1=val1&key2=val2. For example, in https://example.com/api?name=John&age=30, “name=John&age=30” is the query string.
- Request Body: According to the HTTP specification, the original intention of the GET request is to obtain resources, and its request body is usually empty (although technically it is allowed to exist, most servers will ignore or not process the data in the GET request body).
- Characteristics:
- Data is exposed in the URL, can be cached by the browser, recorded in the history, and has security risks (not suitable for transmitting sensitive information).
- It is limited by the length of the URL (different browsers/servers have different limits, generally short), so it is not suitable for transmitting large amounts of data.
Post:
- Data location: Data is mainly placed in the request body, and common encoding methods include:
- application/x-www-form-urlencoded: in the form of key-value pairs (such as name=John&age=30).
- multipart/form-data: used in complex scenarios such as file uploads.
- application/json: sending structured data (such as {“name”:”John”,”age”:30}).
- Query String: It is generally empty, but not absolutely prohibited. In actual development, if there are a small number of parameters (such as env=prod to distinguish environments), they can also be placed in the URL, but the main data is still passed through the request body.
- Characteristics:
- Data is not exposed in the URL, which is relatively safe and suitable for transmitting sensitive information or large amounts of data (such as files, complex forms).
- There is no fixed length limit (actually affected by server configuration).
In general, Get’s data is passed through the query string of the URL, and the Body is generally empty; Post’s data is passed through the Body, and the query string is generally empty.
- Idempotence
- GET: It is an idempotent request method, which means that executing the same GET request multiple times will have the same effect and obtain the same result, and will not change the resources on the server. For example, refreshing the same web page multiple times, the content returned by the server is usually the same.
- POST: It is generally not idempotent. Submitting the same POST request multiple times may create multiple identical resources on the server or update resources multiple times. For example, submitting an order form multiple times may generate multiple orders.
Idempotence in HTTP methods means that executing the same request multiple times has the same effect as executing it once.
Get is to obtain resources from the server, such as visiting a web page. At this time, it is necessary to ensure that when the user refreshes the web page multiple times, the content returned by the server is the same. Therefore, the Get request method is idempotent.
Post is to send resources to the server, such as submitting a form. If it is submitted multiple times, the server will consider it as multiple tasks, because multiple orders will be generated, so the Post request method is not idempotent.
- Caching
- GET: It is usually cached by the browser, which helps improve performance and reduce server load. When the same GET request is initiated again, the browser can directly obtain the response result from the cache without re-sending the request to the server. The caching strategy can be controlled by setting response header information (such as Cache-Control, Expires).
- POST: It is not cached by the browser by default, because POST requests are generally used to modify resources on the server, and the results of each request may be different, so caching is meaningless.
The idempotence of Get ensures that the effect of multiple executions is consistent with that of one execution, so it can be cached by the browser.
If Get is not idempotent, the result of multiple executions cannot be represented by the result of one execution, and the result cached in the browser will naturally be invalid.
- Length and size
- GET: It is limited by the length of the URL. Different browsers and servers have different maximum length limits for URLs, generally around 2000 characters. Therefore, the amount of data transmitted by GET requests is small.
- POST: There is no theoretical limit on data length. The actual amount of data transmitted depends on the server configuration and processing capacity. However, the server may limit the size of the request body to prevent malicious attacks or resource exhaustion.
- Form comparison
| Comparison Dimension | GET | POST |
| Design Semantics | Safe: Only used to obtain resources and should not modify the server state (such as querying data). | Unsafe: Used to submit data and will modify server resources (such as creating/updating data). |
| Idempotence | Idempotent: Multiple requests have the same result and will not have side effects on resources (such as repeated queries). | Non-idempotent: Multiple requests may lead to multiple changes in resources (such as repeated submission of orders to generate multiple data). |
| Data Location | Parameters are attached to the URL (?key=value&…), visible and limited by the URL length. | Parameters are placed in the request body, not exposed in the URL, and theoretically have no length limit. |
| Caching Strategy | Browsers cache GET responses by default, and caching behavior can be controlled through Cache-Control. | Browsers do not cache POST responses by default unless explicitly set (rarely cached in practice). |
| History and Bookmarks | URLs are recorded by browsers and can be added to bookmarks for easy sharing. | Request body data is not recorded, and submission operations cannot be directly reproduced through bookmarks. |
| SEO Friendliness | URLs can be crawled by search engines, suitable for obtaining public resources (such as web pages, API data). | Request body data cannot be crawled, not suitable for scenarios that need to be indexed. |