HTTP Methods Explained: GET, POST, PUT, and DELETE

In modern backend development and microservice architectures, the HTTP protocol serves not only as the vehicle for data exchange but also as the foundation for defining resource operation logic. Spring Boot, the framework for building modern Java web applications, heavily relies on HTTP methods to distinguish the correctness, idempotency, and security of different business intents. A deep understanding of the differences and application scenarios of these four core methods—GET, POST, PUT, and DELETE—is an essential skill for developing high-quality RESTful APIs.
The GET method is used to retrieve a specified resource. In Spring Boot, this operation is typically triggered by mapping request paths using the @GetMapping annotation. Its most significant characteristic is idempotency, meaning that executing the same GET request multiple times produces exactly the same result without causing side effects on the server or generating cumulative effects.

Due to this property, the GET method strictly prohibits passing sensitive information or personally identifiable information (PII) in the URL. Any data requiring parameters should be transmitted via HTTP Headers. Furthermore, to optimize browser caching performance, developers can configure the response header Cache-Control in the Spring Boot configuration file to enable effective caching of static resources or query results.

@GetMapping("/users")
public List<User> getAllUsers() {
    return userService.findAll();
}

POST: Non-Idempotent Creation of New Resources

The POST method is primarily used to submit new data for a specified resource; therefore, it does not possess idempotency. This means that if the same POST request is sent multiple times, the server may create multiple duplicate resource instances. This characteristic makes POST the preferred choice for handling form data, file uploads, and triggering business logic in API calls (such as registering a new user).

In Spring Boot Controller development, the @PostMapping annotation is typically used to handle such requests. The backend service needs to parse the JSON or Form Data within the Request Body and convert it into corresponding entity objects for processing. Unlike GET, the POST method allows parameters to be included in the URL (though best practices still recommend placing complex data in Headers or the Body), but its primary purpose is to carry all context information required for the creation action.

@PostMapping("/users")
public ResponseEntity<User> createUser(@RequestBody User user) {
    return userService.create(user); // Returns the newly created entity and status code
}

PUT: Deterministic Operation for Full Resource Replacement

The PUT method is used to replace a complete resource at a specified location. It also possesses idempotency. Regardless of how many times the caller sends the same PUT request (containing identical data), the server will execute the same final result. This differs from PATCH, which performs partial updates; PUT requires the client to provide a complete state description of the target resource.

In Spring Boot, the @PutMapping annotation is used to define full replacement interfaces. When the received data is incomplete, the common practice is to ignore missing fields or throw an exception, depending on specific business requirements. Since PUT is frequently used to replace an entire entity object, it is often employed as the standard way to implement "delete and rebuild" logic (i.e., first DELETE, then POST).

@PutMapping("/users/{id}")
public ResponseEntity<User> updateUser(@PathVariable Long id, @RequestBody User user) {
    return userService.update(id, user); // Replaces the entire resource object
}

DELETE: Deterministic Operation for Resource Removal

The DELETE method is used to specify the deletion of a resource. It is also idempotent. Even if multiple identical DELETE requests are sent (provided the target resource exists), the result remains consistent—either successfully deleting the resource or returning a "resource not found" status code. This makes DELETE the standard operation for clearing caches, logging out user accounts, or removing order records.

In Spring Boot, the @DeleteMapping annotation is used to handle such requests. Note that the DELETE method typically does not carry a Request Body (as no data needs to be updated) but instead specifies the resource ID to be deleted via path parameters. To enhance security, API designs in production environments often include permission verification logic at the Controller layer to prevent unauthorized users from performing deletion operations.

@DeleteMapping("/users/{id}")
public ResponseEntity<Void> deleteUser(@PathVariable Long id) {
    userService.delete(id); // Returns an empty response or a specific status code indicating success
}

Summary and Best Practice Recommendations

In summary, the correct selection of HTTP methods directly relates to API standardization, maintainability, and client usage experience. In Spring Boot projects, developers should always adhere to RESTful specifications: maintain idempotency when performing resource operations with GET/DELETE/PATCH; avoid placing sensitive information in URLs; and reasonably distinguish between POST (creation) and PUT (full replacement) based on business scenarios. By strictly following these principles, a more robust, standardized, and easily extensible backend service architecture can be constructed.