servlet如何确定何时取消上传？-Howcantheservletdeterminewhenanuploadhasbeencancelled?

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The POST request with the data contains the Content-Length header which tells you the size of the data that is going to be uploaded.

带有数据的POST请求包含Content-Length标头,该标头告诉您要上载的数据的大小。

So when the data stops coming to your server and the size of the data received is less than expected - it would mean that the user (or some network glitch) has canceled the upload.

因此,当数据停止进入您的服务器并且收到的数据大小低于预期时 - 这意味着用户(或某些网络故障)已取消上传。

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If the upload has been cancelled the browser will close the connection, resulting in a an IO exception on the servlet side. For example, in Tomcat it will say "Connection reset by peer" and this is a ClientAbortException. Other servers wrap the IOException differently. Point is just catch the IOException and you should be able to handle it as you wish.

如果上传已被取消,浏览器将关闭连接,导致servlet端出现IO异常。例如,在Tomcat中,它将显示“Connection by peer”,这是ClientAbortException。其他服务器以不同方式包装IOException。 Point只是捕获IOException,你应该能够按照自己的意愿处理它。

Using content-length is not reliable because the HTTP spec does not require content-length headers for POSTs - or for GETs for the matter. Point is, unless you are sure your Javascript XHR sets the header explicitly, this method won't work.

使用内容长度是不可靠的,因为HTTP规范不要求POST的内容长度标题 - 或者GET的内容长度标题。重点是,除非您确定您的Javascript XHR明确设置了标头,否则此方法将无效。

Alternatively you could calculate it yourself and set it to be sure, or even better append your own character stream to the end of a the posted data in the XHR, some unique string of characters, e.g. "jh923k49sk$2#%'. In the servlet, snip off the last 14 characters of the inbound message and check it against the string. If it is the same you know they didn't cancel.

或者你可以自己计算并设置它以确保,或者甚至更好地将你自己的字符流附加到XHR中的发布数据的末尾,一些独特的字符串,例如“jh923k49sk $ 2#%'。在servlet中,剪掉入站消息的最后14个字符并检查字符串。如果它是相同的,你知道它们没有取消。

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I don't see how you can tell, just because a request stream has ended, whether it's done or cancelled. There would have to be a separate HTTP request to indicate cancellation that would have to include some token or ID associated with the upload, since HTTP is stateless and idempotent.

我不知道你怎么知道,只是因为请求流已经结束,无论是完成还是取消。由于HTTP是无状态且幂等的,因此必须有单独的HTTP请求来指示取消,该取消必须包括与上载相关联的一些令牌或ID。