中间件简介
django 中的中间件（middleware），在django中，中间件其实就是一个类，在请求到来和结束后，django会根据自己的规则在合适的时机执行中间件中相应的方法。
在django项目的settings模块中，有一个 MIDDLEWARE_CLASSES 变量，其中每一个元素就是一个中间件
如图：
中间件中一共有五个方法：
process_request
process_view
process_exception
process_response
process_template_response
1、中间件之process_request，process_response
process_request(self,request)
process_response(self, request, response)
当用户发起请求的时候会依次经过所有的的中间件，这个时候的请求时process_request,最后到达views的函数中，views函数处理后，在依次穿过中间件，这个时候是process_response,最后返回给请求者
在django中叫中间件，在其他web框架中，有的叫管道，httphandle
上述截图中的中间件都是django中的，我们也可以自己定义一个中间件，我们可以自己写一个类，但是必须继承MiddlewareMixin
所以需要导入：from django.utils.deprecation import MiddlewareMixin
我们在项目文件下创建一个Middle目录，并在下面创建md.py代码例子如下：
django项目的settings模块
md.py
from django.utils.deprecation import MiddlewareMixin
from django.shortcuts import redirect,render,HttpResponse
class M1(MiddlewareMixin):
def process_request(self,request):
print("M1.process_request")
def process_response(self,request,response):
print("m1.process_response")
return response
class M2(MiddlewareMixin):
def process_request(self,request):
print("M2.process_request") def process_response(self, request, response):
print("m2.process_response")
return response
# 执行结果是：
# M1.process_request
# M2.process_request
# m2.process_response
# m1.process_response
views.py
from django.shortcuts import render,HttpResponse,redirect
from django.forms import Form
from django.forms import fields
from django.forms import widgets def test(request):
print("test")
return HttpResponse("xuyuanyuan")
url.py
urlpatterns = [
url(r'^admin/', admin.site.urls),
url(r'^test.html$', views.test), ]
当页面发起请求时：
pycharm上面显示的运行结果是：
但是如果当请求到达请求2的时候直接不符合条件返回，程序将把请求直接发给中间件2返回，然后依次返回到请求者
用如下图进行理解：
当然这是在django1.10的时候，在之前的版本的时候是直接返回到最后一个中间件的response,然后向上依次返回，最后到发起请求
示例：
md.py
from django.utils.deprecation import MiddlewareMixin
from django.shortcuts import redirect,render,HttpResponse class M1(MiddlewareMixin):
def process_request(self,request):
print("M1.process_request")
def process_view(self,request,callback,callback_args,callback_kwargs):
print("M1.process_view") def process_response(self,request,response):
print("m1.process_response")
return response class M2(MiddlewareMixin):
def process_request(self,request):
print("M2.process_request")
return M2.process_request
def process_view(self,request,callback,callback_args,callback_kwargs):
print("M2.process_view")
# response=callback(request,*callback_args,**callback_kwargs)
# return response
def process_response(self,request,response):
print("m2.process_response")
# return response class M3(MiddlewareMixin):
def process_request(self, request):
print("M3.process_request") def process_view(self, request, callback, callback_args, callback_kwargs):
print("M3.process_view") def process_response(self, request, response):
print("m3.process_response")
return response
执行结果是：
解释说明：
# 执行结果是：（ 在django现在的版本中，因为在m2中 def process_request(self,request):
# print("M2.process_request")
# return M2.process_request有返回值，故而遇到返回值就直接找到自己的response返回）
# M1.process_request
# M2.process_request
# m2.process_response
# m1.process_response
# （ 在django以前的版本，因为在m2中 def process_request(self,request):
# print("M2.process_request")
# return M2.process_request有返回值，故而遇到返回值就直接找到最后的一个response返回，
# 故而执行结果会变成：
# M1.process_request
# M2.process_request
# m3.process_response
# m2.process_response
# m1.process_response）
2、中间件之process_view
process_view(self, request, callback, callback_args, callback_kwargs)
我们在md.py文件中的的代码进行更改：
示例一：
md.py
class M1(MiddlewareMixin):
def process_request(self,request):
print("M1.process_request")
def process_view(self,request,callback,callback_args,callback_kwargs):
print("M1.process_view")
# response=callback(request,*callback_args,**callback_kwargs)
# return response
def process_response(self,request,response):
print("m1.process_response")
return response class M2(MiddlewareMixin):
def process_request(self,request):
print("M2.process_request")
def process_view(self,request,callback,callback_args,callback_kwargs):
print("M2.process_view")
response=callback(request,*callback_args,**callback_kwargs)
return response
def process_response(self,request,response):
print("m2.process_response")
return response
# 执行结果是：
# M1.process_request
# M2.process_request
# M1.process_view
# M2.process_view
# test
# m2.process_response
# m1.process_response
示例二：
class M1(MiddlewareMixin):
def process_request(self,request):
print("M1.process_request")
def process_view(self,request,callback,callback_args,callback_kwargs):
print("M1.process_view")
response=callback(request,*callback_args,**callback_kwargs)
return response
def process_response(self,request,response):
print("m1.process_response")
return response class M2(MiddlewareMixin):
def process_request(self,request):
print("M2.process_request")
def process_view(self,request,callback,callback_args,callback_kwargs):
print("M2.process_view")
response=callback(request,*callback_args,**callback_kwargs)
return response
def process_response(self,request,response):
print("m2.process_response")
return response # 执行结果是：
# M1.process_request
# M2.process_request
# M1.process_view
# test
# m2.process_response
# m1.process_response
关系如下图示例：
当最后一个中间的process_request到达路由关系映射之后，返回到中间件1的process_view，然后依次往下，到达views函数，最后通过process_response依次返回到达用户
3、中间件之process_exception
process_exception(self, request, exception)
当views的函数中出现错误时，就会执行process_exception方法
示例：
class M1(MiddlewareMixin):
def process_request(self,request):
print("M1.process_request")
def process_view(self,request,callback,callback_args,callback_kwargs):
print("M1.process_view")
# response=callback(request,*callback_args,**callback_kwargs)
# return response
def process_response(self,request,response):
print("m1.process_response")
return response
def process_exception(self,request,exception):
print("M1.process_exception") class M2(MiddlewareMixin):
def process_request(self,request):
print("M2.process_request")
def process_view(self,request,callback,callback_args,callback_kwargs):
print("M2.process_view")
# response=callback(request,*callback_args,**callback_kwargs)
# return response
def process_response(self,request,response):
print("m2.process_response")
return response
def process_exception(self,request,exception):
print("M2.process_exception")
return HttpResponse("异常处理")
# 执行结果是：
# M1.process_request
# M2.process_request
# M1.process_view
# M2.process_view
# M2.process_exception
# m2.process_response
# m1.process_response
如果在中间中添加了process_exception方法，工作图示为：
这样当用户发起请求的时候到达中间件3的process_request之后会到达urls路由关系映射这里，如果匹配到了就会到中间件1的process_view,然后依次传递到中间件3的process_view,到达view函数。如果view函数中有报错，则会从中间件3依次向上判断每个中间件的process_exception是否能匹配到这个错误信息，如果匹配到则直接返回到最后一个中间件，这里即中间件3的process_response，然后依次返回到用户，如果没有匹配到这个错误则直接在页面显示错误信息。如果view函数中没有错误，则到中间3即最后一个中间件3的process_response，然后依次向上，传到用户
4、中间件之process_template_responseprocess
process_template_response(self,request,response)
只有当views函数中返回的对象中具有render方法，是就会直接process_template_responseprocess
示例一：
views.py
from django.shortcuts import render,HttpResponse,redirect
from django.forms import Form
from django.forms import fields
# =======在函数中添加render，使md.py文件里的def process_template_response函数执行
class JSONResponse:
def __init__(self,req,status,msg):
self.req=req
self.status=status
self.msg=msg
def render(self):
import json
ret={
"status":self.status,
"msg":self.msg
}
return HttpResponse(json.dump(ret)) def test(request):
ret={}
return JSONResponse(request,True,"哈哈哈哈，错了吧")
md.py
from django.utils.deprecation import MiddlewareMixin
from django.shortcuts import redirect,render,HttpResponse
class M1(MiddlewareMixin):
def process_request(self,request):
print("M1.process_request")
def process_view(self,request,callback,callback_args,callback_kwargs):
print("M1.process_view") def process_response(self,request,response):
print("m1.process_response")
return response
def process_exception(self,request,exception):
print("M1.process_exception") def process_template_response(self,request,response):
"""
如果视图函数的返回值中，有render方法，则会执行该函数
:param request:
:param response:
:return:
"""
print("M1.process_template_response")
return response class M2(MiddlewareMixin):
def process_request(self,request):
print("M2.process_request")
def process_view(self,request,callback,callback_args,callback_kwargs):
print("M2.process_view")
# response=callback(request,*callback_args,**callback_kwargs)
# return response
def process_response(self,request,response):
print("m2.process_response")
return response
def process_exception(self,request,exception):
print("M2.process_exception")
return HttpResponse("异常处理")
def process_template_response(self,request,response):
"""
如果视图函数的返回值中，有render方法，则会执行该函数
:param request:
:param response:
:return:
"""
print("M2.process_template_response")
return response
# 执行结果是：在页面显示“异常处理”，
# def process_exception(self,request,exception):
# print("M1.process_exception")该函数未执行，由于
# def process_exception(self, request, exception):
# print("M2.process_exception")
# return HttpResponse("异常处理")
# 在M2中有return返回值
# 终端上的执行结果是：
# M1.process_request
# M2.process_request
# M1.process_view
# M2.process_view
# M2.process_template_response
# M1.process_template_response
# M2.process_exception
# m2.process_response
# m1.process_response
页面上的结果为：
后台显示：
示例二：
views.py
from django.shortcuts import render,HttpResponse,redirect
from django.forms import Form
from django.forms import fields
from django.forms import widgets # =======在函数中添加render，使md.py文件里的def process_template_response函数执行
class JSONResponse:
def __init__(self,req,status,msg):
self.req=req
self.status=status
self.msg=msg
def render(self):
import json
ret={
"status":self.status,
"msg":self.msg
}
return HttpResponse(json.dump(ret)) def test(request):
ret={}
return JSONResponse(request,True,"哈哈哈哈，错了吧")
md.py
class M1(MiddlewareMixin):
def process_request(self,request):
print("M1.process_request") def process_view(self,request,callback,callback_args,callback_kwargs):
print("M1.process_view") def process_response(self,request,response):
print("m1.process_response")
return response
def process_exception(self,request,exception):
print("M1.process_exception")
return HttpResponse("异常处理")
def process_template_response(self,request,response):
"""
如果视图函数的返回值中，有render方法，则会执行该函数
:param request:
:param response:
:return:
"""
print("M1.process_template_response")
return response class M2(MiddlewareMixin):
def process_request(self,request):
print("M2.process_request")
def process_view(self,request,callback,callback_args,callback_kwargs):
print("M2.process_view")
# response=callback(request,*callback_args,**callback_kwargs)
# return response
def process_response(self,request,response):
print("m2.process_response")
# return response
def process_exception(self,request,exception):
print("M2.process_exception") def process_template_response(self,request,response):
"""
如果视图函数的返回值中，有render方法，则会执行该函数
:param request:
:param response:
:return:
"""
print("M2.process_template_response")
return response
# 执行结果是：在页面显示“异常处理”，所有的函数都执行了
# 终端上的执行结果是：
# M1.process_request
# M2.process_request
# M1.process_view
# M2.process_view
# M2.process_template_response
# M1.process_template_response
# M2.process_exception
# M1.process_exception
# m2.process_response
# m1.process_response