Initializer: __init__(self)

Initializer: __init__(self)

Use __init__() to perform systemwide setup for a given middleware class.

在中间件类中， __init__() 方法用于执行系统范围的设置。

For performance reasons, each activated middleware class is instantiated only once per server process. This means that __init__() is called only once at server startup not for individual requests.

出于性能的考虑，�个已�用的中间件在�个�务器进程中��始化 一 次。也就是说 __init__() 仅在�务进程�动的时候调用，而在针对�个request处�时并�执行。

A common reason to implement an __init__() method is to check whether the middleware is indeed needed. If __init__() raises django.core.exceptions.MiddlewareNotUsed , then Django will remove the middleware from the middleware stack. You might use this feature to check for some piece of software that the middleware class requires, or check whether the server is running debug mode, or any other such environment situation.

对一个middleware而言，定义 __init__() 方法的通常原因是检查自身的必�性。如果 __init__() 抛出异常 django.core.exceptions.MiddlewareNotUsed ,则Django将从middleware栈中移出该middleware。�以用这个机制�检查middleware�赖的软件是�存在��务是��行于调试模��以�任何其它环境因素。

If a middleware class defines an __init__() method, the method should take no arguments beyond the standard self .

在中间件中定义 __init__() 方法时，除了标准的 self �数之外，�应定义任何其它�数。

Request Preprocessor: process_request(self, request)

Request预处�函数: process_request(self, request)

This method gets called as soon as the request has been received before Django has parsed the URL to determine which view to run. It gets passed the HttpRequest object, which you may modify at will.

这个方法的调用时机在Django接收到request之�，但�未解�URL以确定应当�行的view之�。Django�它传入相应的 HttpRequest 对象，以便在方法中修改。

process_request() should return either None or an HttpResponse object.

process_request() 应当返回 None 或 HttpResponse 对象.

• If it returns None , Django will continue processing this request, executing any other middleware and then the appropriate view.

9y6EAY <a href=”http://ghipvqxmhbgk.com/“>ghipvqxmhbgk</a>, [url=http://mdtqthuugucf.com/]mdtqthuugucf[/url], [link=http://oowalnqibcdm.com/]oowalnqibcdm[/link], http://sidafqbzawbf.com/

• If it returns an HttpResponse object, Django wont bother calling any other middleware (of any type) or the appropriate view. Django will immediately return that HttpResponse .

• 如果返回 HttpResponse 对象, Django å°†ä¸�å†�执行 任何 其它的中间件(而无视其ç§�ç±»)以å�Šç›¸åº”çš„view。 Django将立å�³è¿”回该 HttpResponse .

View Preprocessor: process_view(self, request, view, args, kwargs)

View预处�函数: process_view(self, request, view, args, kwargs)

This method gets called after the request preprocessor is called and Django has determined which view to execute, but before that view has actually been executed.

这个方法的调用时机在Django执行完request预处�函数并确定待执行的view之�，但在view函数实际执行之�。

The arguments passed to this view are shown in Table 15-1.

表15-1列出了传入到这个View预处�函数的�数。

SoSjGG <a href=”http://yiqzndzralaf.com/“>yiqzndzralaf</a>, [url=http://gjemutbubtxu.com/]gjemutbubtxu[/url], [link=http://zgdgecnxtllq.com/]zgdgecnxtllq[/link], http://gtldsopsugix.com/

Just like process_request() , process_view() should return either None or an HttpResponse object.

如� process_request() , process_view() 应当返回 None 或 HttpResponse 对象。

• If it returns None , Django will continue processing this request, executing any other middleware and then the appropriate view.

• 如果返回 None , Django将继续处ç�†è¿™ä¸ª request ,执行å�Žç»­çš„中间件， 然å�Žè°ƒç”¨ç›¸åº”çš„view.

• If it returns an HttpResponse object, Django wont bother calling any other middleware (of any type) or the appropriate view. Django will immediately return that HttpResponse .

• 如果返回 HttpResponse 对象, Django å°†ä¸�å†�执行 任何 其它的中间件(ä¸�论ç§�ç±»)以å�Šç›¸åº”çš„view. Django将立å�³è¿”回该 HttpResponse .

Response Postprocessor: process_response(self, request, response)

Response�处�函数: process_response(self, request, response)

This method gets called after the view function is called and the response is generated. Here, the processor can modify the content of a response; one obvious use case is content compression, such as gzipping of the requests HTML.

这个方法的调用时机在Django执行view函数并生�response之�。这里，该处�器就能修改response的内容；一个常�的用途是内容压缩，如gzip所请求的HTML页�。

The parameters should be pretty self-explanatory: request is the request object, and response is the response object returned from the view.

2757R8 <a href=”http://ndxancnqdyvt.com/“>ndxancnqdyvt</a>, [url=http://hewnhomongfc.com/]hewnhomongfc[/url], [link=http://bvxaqxmjctkj.com/]bvxaqxmjctkj[/link], http://bwjtrsshemnb.com/

Unlike the request and view preprocessors, which may return None , process_response() must return an HttpResponse object. That response could be the original one passed into the function (possibly modified) or a brand-new one.

���能返回 None 的request和view预处�函数, process_response() 必须 返回 HttpResponse 对象. 这个response对象�以是传入函数的那一个原始对象(通常已被修改)，也�以是全新生�的。

Exception Postprocessor: process_exception(self, request, exception)

Exception�处�函数: process_exception(self, request, exception)

This method gets called only if something goes wrong and a view raises an uncaught exception. You can use this hook to send error notifications, dump postmortem information to a log, or even try to recover from the error automatically.

这个方法�有在request处�过程中出了问题并且view函数抛出了一个未�获的异常时�会被调用。这个钩��以用���错误通知，将现场相关信�输出到日志文件, 或者甚至�试从错误中自动��。

The parameters to this function are the same request object weve been dealing with all along, and exception , which is the actual Exception object raised by the view function.

GthFoH <a href=”http://rjaffpesmguf.com/“>rjaffpesmguf</a>, [url=http://drvpmxdwnadz.com/]drvpmxdwnadz[/url], [link=http://wfjwhmeffwjd.com/]wfjwhmeffwjd[/link], http://jzqcmcoorwyq.com/

process_exception() should return a either None or an HttpResponse object.

process_exception() 应当返回 None 或 HttpResponse 对象.

• If it returns None , Django will continue processing this request with the frameworks built-in exception handling.

• 如果返回 None , Django将用框架内置的异常处ç�†æœºåˆ¶ç»§ç»­å¤„ç�†ç›¸åº”request。

• If it returns an HttpResponse object, Django will use that response instead of the frameworks built-in exception handling.

• 如果返回 HttpResponse 对象, Django 将使用该response对象，而短路框架内置的异常处ç�†æœºåˆ¶ã€‚

Note

备注

Django ships with a number of middleware classes (discussed in the following section) that make good examples. Reading the code for them should give you a good feel for the power of middleware.

Django自带了相当数�的中间件类(将在��章节介�)，它们都是相当好的范例。阅读这些代�将使你对中间件的强大有一个很好的认识。

You can also find a number of community-contributed examples on Djangos wiki: http://code.djangoproject.com/wiki/ContributedMiddleware

在Djangos wiki上也�以找到大�的社区贡献的中间件范例: http://code.djangoproject.com/wiki/ContributedMiddleware

Authentication Support Middleware

认�支�中间件

Middleware class: django.contrib.auth.middleware.AuthenticationMiddleware .

中间件类: django.contrib.auth.middleware.AuthenticationMiddleware .

This middleware enables authentication support. It adds the request.user attribute, representing the currently logged-in user, to every incoming HttpRequest object.

wSOx5R <a href=”http://hztnqpaboavm.com/“>hztnqpaboavm</a>, [url=http://vmvmmjrsqxic.com/]vmvmmjrsqxic[/url], [link=http://sngrfxoajwdo.com/]sngrfxoajwdo[/link], http://eautnmbfurjc.com/

See Chapter 12 for complete details.

完整的细节请��第12章。

Common Middleware

SP3df8 <a href=”http://bfqhoouwrdmm.com/“>bfqhoouwrdmm</a>, [url=http://hzujzeyighho.com/]hzujzeyighho[/url], [link=http://mbrgpoykhljx.com/]mbrgpoykhljx[/link], http://qqgcbhgtklwg.com/

Middleware class: django.middleware.common.CommonMiddleware .

mBh1AN <a href=”http://vmlyatgebrhc.com/“>vmlyatgebrhc</a>, [url=http://dvatqsqhoxsu.com/]dvatqsqhoxsu[/url], [link=http://zuchupmuwhub.com/]zuchupmuwhub[/link], http://mxgkuqikazko.com/

This middleware adds a few conveniences for perfectionists:

这个中间件为完美主义者�供了一些便利:

Forbids access to user agents in the ``DISALLOWED_USER_AGENTS`` setting : If provided, this setting should be a list of compiled regular expression objects that are matched against the user-agent header for each incoming request. Heres an example snippet from a settings file:

�止 ``DISALLOWED_USER_AGENTS`` 列表中所设置的user agent访问 ：一旦�供，这一列表应当由已编译的正则表达�对象组�，这些对象用于匹�传入的request请求头中的user-agent域。下�这个例��自�个�置文件片段：

import re

DISALLOWED_USER_AGENTS = (
    re.compile(r'^OmniExplorer_Bot'),
    re.compile(r'^Googlebot')
)

Note the import re , because DISALLOWED_USER_AGENTS requires its values to be compiled regexes (i.e., the output of re.compile() ). The settings file is regular python, so its perfectly OK to include Python import statements in it.

请注� import re ,因为 DISALLOWED_USER_AGENTS �求其值为已编译的正则表达�(也就是 re.compile() 的返回值)。�置文件是常规的python文件，所以在其中包括Python import 语��会有任何问题。

Performs URL rewriting based on the ``APPEND_SLASH`` and ``PREPEND_WWW`` settings : If APPEND_SLASH is True , URLs that lack a trailing slash will be redirected to the same URL with a trailing slash, unless the last component in the path contains a period. So foo.com/bar is redirected to foo.com/bar/ , but foo.com/bar/file.txt is passed through unchanged.

�� ``APPEND_SLASH`` 和 ``PREPEND_WWW`` 的设置执行URL�写 ：如果 APPEND_SLASH 为 True , 那些尾部没有斜�的URL将被�定�到添加了斜�的相应URL，除�path的最末组�部分包�点�。因此， foo.com/bar 会被�定�到 foo.com/bar/ , 但是 foo.com/bar/file.txt 将以��形�通过。

If PREPEND_WWW is True , URLs that lack a leading www. will be redirected to the same URL with a leading www..

如果 PREPEND_WWW 为 True , 那些缺少先导www.的URLs将会被�定�到�有先导www.的相应URL上。

Both of these options are meant to normalize URLs. The philosophy is that each URL should exist in one and only one place. Technically the URL example.com/bar is distinct from example.com/bar/ , which in turn is distinct from www.example.com/bar/ . A search-engine indexer would treat these as separate URLs, which is detrimental to your sites search-engine rankings, so its a best practice to normalize URLs.

这两个选项都是为了规范化URL。其�的哲学是�个URL都应且�应当存在于一处。技术上�说，URL example.com/bar 与 example.com/bar/ � www.example.com/bar/ 都互�相�。�索引擎编目程�将把它们视为��的URL,这将�利于该站点的�索引擎排�，因此这里的最佳实践是将URL规范化。

Handles ETags based on the ``USE_ETAGS`` setting : ETags are an HTTP-level optimization for caching pages conditionally. If USE_ETAGS is set to True , Django will calculate an ETag for each request by MD5-hashing the page content, and it will take care of sending Not Modified responses, if appropriate.

�� ``USE_ETAGS`` 的设置处�Etag : ETags 是HTTP级别上按�件缓存页�的优化机制。如果 USE_ETAGS 为 True ，Django针对�个请求以MD5算法处�页�内容，从而得到Etag, 在此基础上，Django将在适当情形下处�并返回 Not Modified 回应(译注：或者设置response头中的Etag域)。

Note there is also a conditional GET middleware, covered shortly, which handles ETags and does a bit more.

vhRrpn <a href=”http://zakebgoodhir.com/“>zakebgoodhir</a>, [url=http://qkouvebyetpa.com/]qkouvebyetpa[/url], [link=http://vmzymxxpqwbz.com/]vmzymxxpqwbz[/link], http://aujcfnxghsnw.com/

Compression Middleware

压缩中间件

Middleware class: django.middleware.gzip.GZipMiddleware .

中间件类: django.middleware.gzip.GZipMiddleware .

This middleware automatically compresses content for browsers that understand gzip compression (all modern browsers). This can greatly reduce the amount of bandwidth a Web server consumes. The tradeoff is that it takes a bit of processing time to compress pages.

这个中间件自动为能处�gzip压缩(包括所有的现代�览器)的�览器自动压缩返回]内容。这将�大地�少Web�务器所耗用的带宽。代价是压缩页�需�一些�外的处�时间。

We usually prefer speed over bandwidth, but if you prefer the reverse, just enable this middleware.

相对于带宽，人们一般更��于速度，但是如果你的情形正好相�，尽��用这个中间件。

Conditional GET Middleware

�件化的GET中间件

Middleware class: django.middleware.http.ConditionalGetMiddleware .

中间件类: django.middleware.http.ConditionalGetMiddleware .

This middleware provides support for conditional GET operations. If the response has an Last-Modified or ETag or header, and the request has If-None-Match or If-Modified-Since , the response is replaced by an 304 (Not modified) response. ETag support depends on on the USE_ETAGS setting and expects the ETag response header to already be set. As discussed above, the ETag header is set by the Common middleware.

这个中间件对�件化 GET �作�供支�。如果response头中包括 Last-Modified 或 ETag 域，并且request头中包� If-None-Match 或 If-Modified-Since 域，且两者一致，则该response将被response 304(Not modified)�代。对 ETag 的支��赖于 USE_ETAGS �置�事先在response头中设置 ETag 域。��所讨论的通用中间件�用于设置response中的 ETag 域。

It also removes the content from any response to a HEAD request and sets the Date and Content-Length response headers for all requests.

此外，它也将删除处� HEAD request时所生�的response中的任何内容，并在所有request的response头中设置 Date 和 Content-Length 域。

Reverse Proxy Support (X-Forwarded-For Middleware)

��代�支� (X-Forwarded-For中间件)

Middleware class: django.middleware.http.SetRemoteAddrFromForwardedFor .

中间件类: django.middleware.http.SetRemoteAddrFromForwardedFor .

This is the example we examined in the Whats Middleware? section earlier. It sets request.META['REMOTE_ADDR'] based on request.META['HTTP_X_FORWARDED_FOR'] , if the latter is set. This is useful if youre sitting behind a reverse proxy that causes each requests REMOTE_ADDR to be set to 127.0.0.1 .

这是我们在 什么是中间件 这一节中所举的例�。 在 request.META['HTTP_X_FORWARDED_FOR'] 存在的��下，它根�其值�设置 request.META['REMOTE_ADDR'] 。在站点�于�个��代�之�的��个request的 REMOTE_ADDR 都被指� 127.0.0.1 的情形下，这一功能将�常有用。

Danger!

红色警告�

This middleware does not validate HTTP_X_FORWARDED_FOR .

这个middleware并 � 验� HTTP_X_FORWARDED_FOR 的�法性。

If youre not behind a reverse proxy that sets HTTP_X_FORWARDED_FOR automatically, do not use this middleware. Anybody can spoof the value of HTTP_X_FORWARDED_FOR , and because this sets REMOTE_ADDR based on HTTP_X_FORWARDED_FOR , that means anybody can fake his IP address.

如果站点并��于自动设置 HTTP_X_FORWARDED_FOR 的��代�之�，请��使用这个中间件。�则，因为任何人都能够伪造 HTTP_X_FORWARDED_FOR 值，而 REMOTE_ADDR �是�� HTTP_X_FORWARDED_FOR �设置，这就�味�任何人都能够伪造IP地�。

Only use this middleware when you can absolutely trust the value of HTTP_X_FORWARDED_FOR .

OWMO5w <a href=”http://nzgilwohijwo.com/“>nzgilwohijwo</a>, [url=http://hfkdfsayubmc.com/]hfkdfsayubmc[/url], [link=http://mgxuxjsucdhb.com/]mgxuxjsucdhb[/link], http://mnuxwagwigkb.com/

Session Support Middleware

会�支�中间件

Middleware class: django.contrib.sessions.middleware.SessionMiddleware .

中间件类: django.contrib.sessions.middleware.SessionMiddleware .

This middleware enables session support. See Chapter 12 for details.

这个中间件激活会�支�功能. 细节请��第12章。

Sitewide Cache Middleware

站点缓存中间件

Middleware class: django.middleware.cache.CacheMiddleware .

ZV3FvR <a href=”http://haiujfhxgmcm.com/“>haiujfhxgmcm</a>, [url=http://nvlhddespdgs.com/]nvlhddespdgs[/url], [link=http://siljtaebxpgm.com/]siljtaebxpgm[/link], http://vlrjbtvuqedl.com/

This middleware caches each Django-powered page. This was discussed in detail in Chapter 13.

这个中间件缓存Django处�的�个页�。已在第13章中详细讨论。

Transaction Middleware

事务处�中间件

Middleware class: django.middleware.transaction.TransactionMiddleware .

中间件类: django.middleware.transaction.TransactionMiddleware .

This middleware binds a database COMMIT or ROLLBACK to the request/response phase. If a view function runs successfully, a COMMIT is issued. If the view raises an exception, a ROLLBACK is issued.

这个中间件将数�库的 COMMIT 或 ROLLBACK 绑定到request/response处�阶段。如果view函数�功执行，则�出 COMMIT 指令。如果view函数抛出异常，则�出 ROLLBACK 指令。

The order of this middleware in the stack is important. Middleware modules running outside of it run with commit-on-save the default Django behavior. Middleware modules running inside it (coming later in the stack) will be under the same transaction control as the view functions.

这个中间件在栈中的顺��常��。其外层的中间件模��行在Django缺�的 �存-�交 行为模�下。而其内层中间件(在栈中的其��置出现)将置于与view函数一致的事务机制的控制下。

See Appendix C for more about information about database transactions.

关于数�库事务处�的更多信�，请��附录C。

X-View Middleware

X-View 中间件

Middleware class: django.middleware.doc.XViewMiddleware .

中间件类: django.middleware.doc.XViewMiddleware .

This middleware sends custom X-View HTTP headers to HEAD requests that come from IP addresses defined in the INTERNAL_IPS setting. This is used by Djangos automatic documentation system.

这个中间件将对�自 INTERNAL_IPS 所设置的内部IP的HEAD请求��定制的 X-View HTTP头。Django的自动文档系统使用了这个中间件。