如何在Java中使用W3C DOM创建一个空的DOCTYPE？
[英]How to create an empty DOCTYPE using W3C DOM in Java?
问题描述
I am trying to read an XML document and output it into a new XML document using the W3C DOM API in Java . 
我正在尝试使用Java中的W3C DOM API读取XML文档并将其输出到新的XML文档中 。 To handle DOCTYPEs, I am using the following code (from an input Document doc to a target File target ): 要处理DOCTYPE，我使用以下代码（从输入Document doc到目标File target ）：
TransformerFactory transfac = TransformerFactory.newInstance();
Transformer trans = transfac.newTransformer();
trans.setOutputProperty(OutputKeys.OMIT_XML_DECLARATION, "no"); // omit '<?xml version="1.0"?>'
trans.setOutputProperty(OutputKeys.INDENT, "yes");
// if a doctype was set, it needs to persist
if (doc.getDoctype() != null) {
DocumentType doctype = doc.getDoctype();
trans.setOutputProperty(OutputKeys.DOCTYPE_SYSTEM, doctype.getSystemId());
trans.setOutputProperty(OutputKeys.DOCTYPE_PUBLIC, doctype.getPublicId());
}
FileWriter sw = new FileWriter(target);
StreamResult result = new StreamResult(sw);
DOMSource source = new DOMSource(doc);
trans.transform(source, result);
This works fine for both XML documents with and without DOCTYPEs. 对于包含和不包含DOCTYPE的XML文档，这都适用。 However, I am now coming across a NullPointerException when trying to transform the following input XML document: 但是，在尝试转换以下输入XML文档时，我现在遇到NullPointerException ：
<?xml version='1.0' encoding='UTF-8'?>
<!DOCTYPE permissions >
<permissions>
// ...
</permissions>
HTML 5 uses a similar syntax for its DOCTYPEs, and it is valid . HTML 5对其DOCTYPE使用类似的语法， 它是有效的 。 But I have no idea how to handle this using the W3C DOM API - trying to set the DOCTYPE_SYSTEM to null throws an exception. 但我不知道如何使用W3C DOM API处理这个问题 - 尝试将DOCTYPE_SYSTEM设置为null会引发异常。 Can I still use the W3C DOM API to output an empty doctype? 我还可以使用W3C DOM API输出空的doctype吗？
2 个解决方案
解决方案1
4 2014-05-21 19:48:48
Although this question is two years old, it is a top search result in some web search engine, so maybe it is a useful shortcut. 虽然这个问题已经有两年了，但它在某些网络搜索引擎中是一个顶级的搜索结果，所以它可能是一个有用的捷径。 See the question Set HTML5 doctype with XSLT referring to http://www.w3.org/html/wg/drafts/html/master/syntax.html#doctype-legacy-string , which says: 请参阅http://www.w3.org/html/wg/drafts/html/master/syntax.html#doctype-legacy-string ，查看使用XSLT设置HTML5 doctype的问题，其中说：
For the purposes of HTML generators that cannot output HTML markup with the short DOCTYPE "
<!DOCTYPE html>", a DOCTYPE legacy string may be inserted into the DOCTYPE [...]<!DOCTYPE html>”输出HTML标记的HTML生成器，可以将DOCTYPE遗留字符串插入DOCTYPE [...]In other words,
<!DOCTYPE html SYSTEM "about:legacy-compat">or<!DOCTYPE html SYSTEM 'about:legacy-compat'>, case-insensitively except for the part in single or double quotes.<!DOCTYPE html SYSTEM "about:legacy-compat">或<!DOCTYPE html SYSTEM 'about:legacy-compat'>，不区分大小写，但单引号或双引号中的部分除外。
Leading to a line of Java code like this: 导致一系列Java代码如下：
trans.setOutputProperty(OutputKeys.DOCTYPE_SYSTEM, "about:legacy-compat");
解决方案2
1 2012-05-25 08:16:07
Try the suggestions here https://stackoverflow.com/a/6637886/116509 . 尝试这里的建议https://stackoverflow.com/a/6637886/116509 。 Basically it looks like it can't be done with standard Java DOM support. 基本上看起来它不能用标准的Java DOM支持来完成。
You can also try StAX 您也可以尝试StAX
XMLStreamWriter xmlStreamWriter =
XMLOutputFactory.newFactory().createXMLStreamWriter( System.out, doc.getXmlEncoding() );
Result result = new StAXResult( xmlStreamWriter );
// ... create dtd String
xmlStreamWriter.writeDTD( dtd );
DOMSource source = new DOMSource( doc );
trans.transform( source, result );
but it's ugly because the DTD parameter is a String , and you only have a DocumentType object. 但它很难看，因为DTD参数是一个String ，而你只有一个DocumentType对象。
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