Flask之請求鉤子的實現

這篇文章主要介紹了Flask之請求鉤子的實現，文中通過示例代碼介紹的非常詳細，對大家的學習或者工作具有一定的參考學習價值，需要的朋友們下面隨着小編來一起學習學習吧

請求鉤子

通過裝飾器爲一個模塊添加請求鉤子, 對當前模塊的請求進行額外的處理. 比如權限驗證.

說白了，就是在執行視圖函數前後你可以進行一些處理，Flask使用裝飾器爲我們提供了註冊通用函數的功能。

1、before_first_request:在處理第一個請求前執行

before_first_request

在對應用程序實例的第一個請求之前註冊要運行的函數, 只會執行一次

  #: A lists of functions that should be called at the beginning of the
  #: first request to this instance. To register a function here, use
  #: the :meth:`before_first_request` decorator.
  #:
  #: .. versionadded:: 0.8
  self.before_first_request_funcs = []

  @setupmethod
  def before_first_request(self, f):
    """Registers a function to be run before the first request to this
    instance of the application.

    .. versionadded:: 0.8
    """
    self.before_first_request_funcs.append(f) 

將要運行的函數存放到before_first_request_funcs 屬性中進行保存

2、before_request:在每次請求前執行

在每個請求之前註冊一個要運行的函數, 每一次請求都會執行

  #: A dictionary with lists of functions that should be called at the
  #: beginning of the request. The key of the dictionary is the name of
  #: the blueprint this function is active for, `None` for all requests.
  #: This can for example be used to open database connections or
  #: getting hold of the currently logged in user. To register a
  #: function here, use the :meth:`before_request` decorator.
  self.before_request_funcs = {} 

  @setupmethod
  def before_request(self, f):
    """Registers a function to run before each request."""
    self.before_request_funcs.setdefault(None, []).append(f)
    return f

將要運行的函數存放在字典中, None 爲鍵的列表中存放的是整個應用的所有請求都要運行的函數.

3、after_request:每次請求之後調用，前提是沒有未處理的異常拋出

在每個請求之後註冊一個要運行的函數, 每次請求都會執行. 需要接收一個 Response 類的對象作爲參數 並返回一個新的Response 對象 或者 直接返回接受到的Response 對象

  #: A dictionary with lists of functions that should be called after
  #: each request. The key of the dictionary is the name of the blueprint
  #: this function is active for, `None` for all requests. This can for
  #: example be used to open database connections or getting hold of the
  #: currently logged in user. To register a function here, use the
  #: :meth:`after_request` decorator.
  self.after_request_funcs = {}

  @setupmethod
  def after_request(self, f):
    """Register a function to be run after each request. Your function
    must take one parameter, a :attr:`response_class` object and return
    a new response object or the same (see :meth:`process_response`).

    As of Flask 0.7 this function might not be executed at the end of the
    request in case an unhandled exception occurred.
    """
    self.after_request_funcs.setdefault(None, []).append(f)
    return f

4、teardown_request:每次請求之後調用，即使有未處理的異常拋出

註冊一個函數在每個請求的末尾運行，不管是否有異常, 每次請求的最後都會執行.

  #: A dictionary with lists of functions that are called after
  #: each request, even if an exception has occurred. The key of the
  #: dictionary is the name of the blueprint this function is active for,
  #: `None` for all requests. These functions are not allowed to modify
  #: the request, and their return values are ignored. If an exception
  #: occurred while processing the request, it gets passed to each
  #: teardown_request function. To register a function here, use the
  #: :meth:`teardown_request` decorator.
  #:
  #: .. versionadded:: 0.7
  self.teardown_request_funcs = {}

  @setupmethod
  def teardown_request(self, f):
    """Register a function to be run at the end of each request,
    regardless of whether there was an exception or not. These functions
    are executed when the request context is popped, even if not an
    actual request was performed.
    """
    self.teardown_request_funcs.setdefault(None, []).append(f)
    return f

將要運行的函數存放在字典中, None 爲鍵的列表中存放的是整個應用的所有請求都要運行的函數.

from flask import Flask
app = Flask(__name__)

@app.before_first_request
def before_first_request():
  print('before_first_request')


@app.before_request
def before_request():
  print('before_request')


@app.after_request
def after_request(resp):
  print('after_request')
  return resp


@app.teardown_request
def teardown_request(e):
  print('teardown_request')


@app.route("/")
def view_fn():
  return "view_fn"
  
if __name__ == "__main__":
  app.run()

第一次請求：

頁面輸出：view_fn
控制檯輸出： before_first_request
            before_request
            after_request
            teardown_request

第二次請求：

頁面輸出：view_fn
控制檯輸出： before_request
            after_request
            teardown_request

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