HTTP Request Methods and Their Differences
Description
HTTP request methods are key fields for clients to express operational intent to servers. Different methods define distinct semantics for resource operations. Common methods include GET, POST, PUT, DELETE, etc. The differences between them and the criteria for their selection in practical applications are frequently tested in interviews.
1. Basic Semantics of Core Methods
- GET: Requests a specified resource. Parameters are passed via the URL (length-limited), and responses can be cached.
- POST: Submits data (e.g., form data) to a specified resource. Data is placed in the request body and may trigger server-side state changes (e.g., creating a resource). By default, responses are not cached.
- PUT: Replaces the entire content of the target resource (requires complete resource data). Creates the resource if it does not exist.
- DELETE: Requests the deletion of a specified resource.
2. Key Characteristics Comparison
| Method | Idempotent | Safe | Data Transmission Method | Cache Support |
|---|---|---|---|---|
| GET | Yes | Yes | URL Query String | Yes |
| POST | No | No | Request Body | No (default) |
| PUT | Yes | No | Request Body | No |
| DELETE | Yes | No | URL or Request Body | No |
3. In-depth Analysis of Idempotence and Safety
- Idempotence: Repeated identical requests have the same effect as a single request (e.g., GET, PUT, DELETE). For example, repeating the same PUT request results in the same final resource state.
- Safety: Requests that do not modify server resources (e.g., GET, HEAD). POST is not safe because it may create resources.
4. Practical Application Scenarios
- GET: Loading web pages, querying data (e.g., search keywords).
- POST: User login (submitting passwords), placing orders.
- PUT: Updating complete user information (e.g., replacing a profile).
- DELETE: Deleting an article or product.
5. Clarifying Common Misconceptions
- Difference between POST and PUT: PUT emphasizes "replacing the entire resource," while POST is more flexible (allowing additional operations). For example, when using PUT to update a user's age, all user fields must be provided; POST can transmit only the age field.
- Caching mechanism: Browsers cache GET responses by default, but caching behavior for other methods can be adjusted via the Cache-Control header.
6. Supplementary Methods
- HEAD: Similar to GET but returns only the response headers (used to check resource existence).
- PATCH: Partially updates a resource (contrasts with PUT's complete replacement).
By understanding the semantics and characteristics of these methods, misuse in actual development (e.g., using GET to submit sensitive data) can be avoided.