etag

Server sends back page A , plus an ETag for A.

服务器返回页面A，并在给A加上一个ETag。

Otherwise , we set the ETag response header in preparation for the next client request .

否则，我们设置ETag响应头以便为下一次客户端请求做好准备。

The origin server specifies the component 's ETag using the ETag response header .

原始服务器通过含有ETag文件头的响应指定页面内容的ETag。

An ETag is a string that uniquely identifies a specific version of a component .

Etag是一个识别内容版本号的唯一字符串。

Client renders the page then caches it , along with the ETag .

客户端展现该页面，并将页面连同ETag一起缓存。

Generally , you should check for concurrent updates by verifying the ETag of the underlying work item .

一般来说，您应该通过验证基础工作项的ETag来检查并发更新。

Client requests page A again , passing along the ETag it got back from the server the last time it made the request .

客户再次请求页面A，并将上次请求时服务器返回的ETag一起传递给服务器。

Because the server generated the ETag in the first place , it can use it later to determine if the page has changed .

因为服务器首先产生ETag，服务器可在稍后使用它来判断页面是否已经被修改。

This is considered good form for server generated content as it caters for clients that don 't understand ETag headers .

这被认为是为服务器产生内容的正确形式，因为其迎合了不认识ETag头的客户端。

And removing the ETag reduces the size of the HTTP headers in both the response and subsequent requests .

去掉ETag文件头会减少响应和下次请求中文件的大小。

We are computing the ETag value after the page has been rendered on the server , but before sending it back to the client .

我们是在页面已经被展现在服务器之后计算ETag的，但是在返回客户端之前。

The ETag response-header field value , an entity tag , provides for an " opaque " cache validator .

ETag响应头部字段值是一个实体标记，它提供一个“不透明”的缓存验证器。

If you 're not taking advantage of the flexible validation model that ETags provide , it 's better to just remove the ETag altogether .

如果你没有使用ETag提供的灵活的验证模式，那么干脆把所有的ETag都去掉会更好。

We use the count as the ETag , so when the client sends it back we know if one of the objects behind the page has been modified .

我们使用该计数值作为ETag，这样当客户端将ETag送回时我们就知道页面背后的一个或多个对象是否被修改了。

The second approach uses a more sophisticated method to track changes in the model used by the view to determine ETag validity ( a " deep ETag " implementation ) .

第二种方法使用更为复杂的方法追踪view中所使用的model，以确定ETag有效性（一个“深入的”ETag实现）。

Public services APIs usually help clients with implementing the caching mechanisms by populating standard HTTP response headers : Cache-Control , Expires , and ETag .

公共服务API通常可帮助客户实现缓存机制，填充标准的HTTP响应标头：Cache-Control、Expires和ETag。

My hope is that this article has provided you with food for thought for your current and future web based projects , and an appreciation for the under utilized ETag response header .

我希望本文已为你当下或将来基于Web的项目提供了精神食粮，并正确评价在底层利用ETag响应头的做法。

This is an ideal place to apply our ETag comparison logic so that if we find the data that is used to build a page hasn 't changed we can avoid further processing .

这儿是应用我们ETag比较逻辑的理想场所，因此如果我们发现构建一个页面的数据没有发生变化，我们可以避免进一步处理。

If there is a ETag match , there really is no need to pull in the data for the model as the rendered page will not be sent to the client .

如果有Etag匹配，实际上并不需要再为model装进数据，因为要展现的页面不需要发送回客户端。

By default , both Apache and IIS embed data in the ETag that dramatically reduces the odds of the validity test succeeding on web sites with multiple servers .

默认情况下，Apache和IIS都会把数据嵌入ETag中，这会显著减少多服务器间的文件验证冲突。

The first approach we will look at is to create a Servlet Filter that will generate its ETag token based on the content of the page-the " View " in MVC .

我们要考虑的第一种方法是创建一个ServletFilter，它将基于页面（MVC中的“View”）的内容产生其ETag记号。

We first make sure we are dealing with a GET request ( ETag in conjunction with PUT can be used to detect conflicting updates , but that is beyond the scope of this article . ) .

我们首先确信我们正在处理GET请求（与PUT一起的ETag可以用来检测不一致的更新，但其超出了本文的范围。）

Server examines the ETag and determines that the page hasn 't changed since last time the client requested it , so sends back a response of304 ( Not Modified ) with an empty body .

服务器检查该ETag，并判断出该页面自上次客户端请求之后还未被修改，直接返回响应304（未修改&NotModified）和一个空的响应体。