HTTP Methods and Status Codes Reference

HTTP Methods

Method	Idempotent	Safe	Purpose	Typical Status
GET	Yes	Yes	Retrieve resource	200, 304, 404
POST	No	No	Create resource	201, 400, 409
PUT	Yes	No	Replace resource	200, 204, 404
PATCH	No	No	Partial update	200, 204, 400
DELETE	Yes	No	Remove resource	204, 404
HEAD	Yes	Yes	Like GET, no body	200, 304, 404
OPTIONS	Yes	Yes	Describe communication options	200

Idempotent Operations

An operation is idempotent if making the same request multiple times produces the same result as making it once.

Safe Operations

A safe operation doesn't change the state of the server. Safe operations are always idempotent.

HTTP Status Codes

2xx Success

200 OK: Successful GET/PUT/PATCH
201 Created: Successful POST (include Location header)
202 Accepted: Async processing accepted
204 No Content: Successful DELETE or POST with no content
206 Partial Content: Range request successful

3xx Redirection

301 Moved Permanently: Resource permanently moved
304 Not Modified: Cache valid, use local copy
307 Temporary Redirect: Temporary redirect

4xx Client Errors

400 Bad Request: Invalid format or parameters
401 Unauthorized: Authentication required
403 Forbidden: Authenticated but not authorized
404 Not Found: Resource doesn't exist
409 Conflict: Constraint violation or conflict
422 Unprocessable Entity: Validation failed (semantic error)
429 Too Many Requests: Rate limit exceeded

5xx Server Errors

500 Internal Server Error: Unexpected server error
502 Bad Gateway: External service unavailable
503 Service Unavailable: Server temporarily down
504 Gateway Timeout: External service timeout

Common REST API Patterns

Resource URLs

GET    /users              # List all users
GET    /users/123           # Get specific user
POST   /users              # Create user
PUT    /users/123           # Update user
DELETE /users/123           # Delete user
GET    /users/123/orders   # Get user's orders

Query Parameters

GET /users?page=0&size=20&sort=createdAt,desc
- page: Page number (0-based)
- size: Number of items per page
- sort: Sorting format (field,direction)

Response Headers

Location: /api/users/123           # For 201 Created responses
X-Total-Count: 45                 # Total items count
Cache-Control: no-cache           # Cache control
Content-Type: application/json     # Response format

Error Response Format

{
  "status": 400,
  "error": "Bad Request",
  "message": "Validation failed: name: Name cannot be blank, email: Valid email required",
  "path": "/api/users",
  "timestamp": "2024-01-15T10:30:00Z"
}

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