在tornado.web.RequestHandler类中的初始构造方法中：
class RequestHandler(object):
"""Base class for HTTP request handlers. Subclasses must define at least one of the methods defined in the
"Entry points" section below.
"""
SUPPORTED_METHODS = ("GET", "HEAD", "POST", "DELETE", "PATCH", "PUT",
"OPTIONS") _template_loaders = {} # type: typing.Dict[str, template.BaseLoader]
_template_loader_lock = threading.Lock()
_remove_control_chars_regex = re.compile(r"[\x00-\x08\x0e-\x1f]") def __init__(self, application, request, **kwargs):
super(RequestHandler, self).__init__() self.application = application
self.request = request
self._headers_written = False
self._finished = False
self._auto_finish = True
self._transforms = None # will be set in _execute
self._prepared_future = None
self._headers = None # type: httputil.HTTPHeaders
self.path_args = None
self.path_kwargs = None
self.ui = ObjectDict((n, self._ui_method(m)) for n, m in
application.ui_methods.items())
# UIModules are available as both `modules` and `_tt_modules` in the
# template namespace. Historically only `modules` was available
# but could be clobbered by user additions to the namespace.
# The template {% module %} directive looks in `_tt_modules` to avoid
# possible conflicts.
self.ui["_tt_modules"] = _UIModuleNamespace(self,
application.ui_modules)
self.ui["modules"] = self.ui["_tt_modules"]
self.clear()
self.request.connection.set_close_callback(self.on_connection_close)
self.initialize(**kwargs)
尾部自动调用tornado为用户预留的initialize方法（未实现，是由用户调用来实现）
def initialize(self):
"""Hook for subclass initialization. Called for each request. A dictionary passed as the third argument of a url spec will be
supplied as keyword arguments to initialize(). Example:: class ProfileHandler(RequestHandler):
def initialize(self, database):
self.database = database def get(self, username):
... app = Application([
(r'/user/(.*)', ProfileHandler, dict(database=database)),
])
"""
pass
所以对于之前的session类的使用上可以用到钩子，就像php中的公共控制类中构造方法中调用某些函数，会在每个控制器执行时去执行这些函数，减少在代码中的复用。
前面session类的改进
class BaseRequestHandler(tornado.web.RequestHandler):
#tornado预留钩子函数
def initialize(self):
self.session=Session(self) class IndexHandler(BaseRequestHandler):
def get(self):
if self.get_argument('u',None) in ['asd','zxc']:
#在这里有个bug,当程序两次设置值时，逻辑相同，但是由于只发送了一次请求，获取了第一次的py_session
#在相同逻辑代码处理下random_str=self.handler.get_cookie('py_session')
#每次都是不正确的，都需要重新创建一个标识符
#但是后面的刷新过程中由于修改了客户区的py_session,所以可以正常进行操作，但是第一次产生的py_session的依旧存在服务端
self.session.set_value('is_login',True)
self.session.set_value('name',self.get_argument('u'))
#self.get_secure_cookie()
#The decoded cookie value is returned as a byte string (unlike
#`get_cookie`).
else:
self.write("请登录")