XML 文件中的特殊字符 - 使用 DOM API 处理
声明：本页面是StackOverFlow热门问题的中英对照翻译，遵循CC BY-SA 4.0协议，如果您需要使用它，必须同样遵循CC BY-SA许可，注明原文地址和作者信息，同时你必须将它归于原作者（不是我）：StackOverFlow
原文地址: http://stackoverflow.com/questions/871963/
Warning: these are provided under cc-by-sa 4.0 license. You are free to use/share it, But you must attribute it to the original authors (not me):
StackOverFlow
Special characters in XML files - processing with the DOM API
提问by user42155
I have a file, which is in XML format (consists just of root start and end tags, and children of the root). The text elements of the children contain the ampersand symbol &. In XML it is not allowed to have this symbol in order the document to be valid, and when I tried to process the file using the DOM API in Java and an XML parser, I obtained parsing errors. Therefore, I have replaced & with &, and I processed the file successfully: I had to extract the values of the text elements in different plain text files.
我有一个 XML 格式的文件（仅由根开始和结束标记以及根的子项组成）。子元素的文本元素包含与符号 &。在 XML 中，为了使文档有效，不允许使用此符号，并且当我尝试使用 Java 中的 DOM API 和 XML 解析器处理文件时，我遇到了解析错误。因此，我将 & 替换为&，并且成功处理了文件：我必须提取不同纯文本文件中文本元素的值。
When I opened these newly created text files, I expected to see &, but there was & instead. Why is this? I have stored the text in text files without any extension (my original file with the XML format also did not have .xml extension), and I do have just & in the text of the new file, no matter how I open the file: as txt or as xml file (these are some of the options in my XML editor). What happens exactly? Does Java (?) convert &to & automatically? Or there is some default encoding? Well, &stands for &, and I suppose there is some "invisible" automatic conversion, but I am confused when and how this happens. Here are examples of my original file and the extracted file which I receive after I processed the original file with Java:
当我打开这些新创建的文本文件时，我希望看到&，但看到的是 & 。为什么是这样？我将文本存储在没有任何扩展名的文本文件中（我的 XML 格式的原始文件也没有 .xml 扩展名），并且无论我如何打开文件，我在新文件的文本中都只有 & ：作为 txt 或 xml 文件（这些是我的 XML 编辑器中的一些选项）。究竟会发生什么？Java (?) 是否&自动转换为 &？或者有一些默认编码？嗯，&代表 &，我想有一些“隐形”自动转换，但我很困惑何时以及如何发生这种情况。以下是我的原始文件和使用 Java 处理原始文件后收到的提取文件的示例：
This is my "negative.review" file in XML format:
这是我的 XML 格式的“negative.review”文件：
<review>
<review_text>
I will not wear it as it is too big & looks funny on me.
</review_text>
</review>
This is my extracted file "negative_1":
这是我提取的文件“negative_1”：
I will not wear it as it is too big & looks funny on me.
For me it is important to have the original data as it is (without doing any conversions/replacements), so I thought that I have to process the extracted file "negative_1" converting back &to &. As you see, it seems I don't have to do this. But I don't understand why :(.
对我来说，保持原始数据原样很重要（不进行任何转换/替换），所以我认为我必须将提取的文件“negative_1”转换回&&。如您所见，我似乎不必这样做。但我不明白为什么:(。
Thank you in advance!
先感谢您！
回答by Tomalak
The reason is simple: The XML file really containsan "&"character.
原因很简单：XML 文件确实包含一个"&"字符。
It is just represented differently (i.e. it is "escaped"), because a real "&"on it's own breaks XML files, as you've seen. Read the relevant section in the XML 1.0 spec: "2.4 Character Data and Markup". It's just a few lines, but it explains the issue quite well.
它只是以不同的方式表示（即它被“转义”），因为"&"正如您所看到的那样，它本身会破坏 XML 文件。阅读 XML 1.0 规范中的相关部分：“2.4 字符数据和标记”。这只是几行，但它很好地解释了这个问题。
XML is a representation of data (!). Don't think of it as a text file. Example:
XML 是数据的表示 (!)。不要将其视为文本文件。例子：
You want to store the string "17 < 20" in an XML file. Initially, you can't, since the "<" is reserved as the opening tag bracket. So this would be invalid:
您想将字符串“17 < 20”存储在 XML 文件中。最初，您不能，因为“<”被保留为开始标记括号。所以这将是无效的：
<xml>17 < 20</xml>
Solution: You employ character escaping on the special/reserved character, just for the means of retaining the validity of the file:
解决方案：您在特殊/保留字符上使用字符转义，只是为了保持文件的有效性：
<xml>17 < 20</xml>
For all practical purposes the above snippet contains the following data (in JSON representation this time):
出于所有实际目的，上述代码段包含以下数据（这次以 JSON 表示）：
{
"xml": "17 < 20"
}
This is why you see the real "&"in your post-processing. It had been escaped in just the same way, but it's meaningstayed the same all the time.
这就是您"&"在后期处理中看到真实的原因。它以同样的方式逃脱，但它的含义一直保持不变。
The above example also explains why the "&"must be treated specially: It is itself part of the XML escaping mechanism. It marks the start of an escape sequence, like in "<". Therefore it must be escaped itself (with "&", like you've done).
上面的例子也解释了为什么"&"必须特殊对待：它本身就是 XML 转义机制的一部分。它标志着一个转义序列的开始，就像在"<". 因此它必须自己转义（使用"&"，就像你所做的那样）。
回答by Alex Martelli
Any XML parser will implicitly translate entities such as &, <, >, into the corresponding characters, as part of the process of parsing the file.
作为解析文件过程的一部分，任何 XML 解析器都会隐式地将&, <, >,等实体转换为相应的字符。
