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這是一個後續的問題Is there some equivalent in Java to Ruby's Nokogiri::XML::EntityDecl?用JDOM讀寫內部的DTD
我有一個簡單的菊花DTBook的XML文件（儘管具體的DTD是不是我的問題很重要，這是使用的實際標準在舊的談話書籍中）。它包含來自DTBook和MathML命名空間的XML。
請注意，DTD聲明遵循從specification for MathML in DAISY複製的慣例，它使用組合的DTD，既引用DTBook標準的外部DTD，也引入MathML標準的一些內部ENTITY定義。
<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE dtbook PUBLIC "-//NISO//DTD dtbook 2005-2//EN"
"http://www.daisy.org/z3986/2005/dtbook-2005-2.dtd"
[
<!ENTITY % MATHML.prefixed "INCLUDE" >
<!ENTITY % MATHML.prefix "m">
<!ENTITY % MATHML.Common.attrib
"xlink:href CDATA #IMPLIED
xlink:type CDATA #IMPLIED
class CDATA #IMPLIED
style CDATA #IMPLIED
id ID #IMPLIED
xref IDREF #IMPLIED
other CDATA #IMPLIED
xmlns:dtbook CDATA #FIXED 'http://www.daisy.org/z3986/2005/dtbook/'
dtbook:smilref CDATA #IMPLIED"
>
<!ENTITY % mathML2 PUBLIC "-//W3C//DTD MathML 2.0//EN"
"http://www.w3.org/Math/DTD/mathml2/mathml2.dtd"
>
%mathML2;
<!ENTITY % externalFlow "| m:math">
<!ENTITY % externalNamespaces "xmlns:m CDATA #FIXED
'http://www.w3.org/1998/Math/MathML'">
]
>
<dtbook xmlns="http://www.daisy.org/z3986/2005/dtbook/" xmlns:m="http://www.w3.org/1998/Math/MathML"
version="2005-2" xml:lang="eng">
<head></head>
<book>
<frontmatter><doctitle></doctitle></frontmatter>
<bodymatter>
<level1>
<p>Test</p>
<m:math xmlns:dtbook="http://www.daisy.org/z3986/2005/dtbook/"
id="math0001" dtbook:smilref="nativemathml.smil#math0001" altimg="nativemathml0001.png"
alttext="sigma-summation UnderScript i equals zero OverScript infinity EndScripts x Subscript i">
<m:mrow>
<m:mstyle displaystyle='true'>
<m:munderover>
<m:mo>∑</m:mo>
<m:mrow>
<m:mi>i</m:mi>
<m:mo>=</m:mo>
<m:mn>0</m:mn>
</m:mrow>
<m:mi>∞</m:mi>
</m:munderover>
<m:mrow>
<m:msub>
<m:mi>x</m:mi>
<m:mi>i</m:mi>
</m:msub>
</m:mrow>
</m:mstyle>
</m:mrow>
</m:math>
</level1>
</bodymatter>
<rearmatter><level1><p></p></level1></rearmatter>
</book>
</dtbook>
我用以下Java代碼讀取文檔並將其打印出來。我第一次使用JDOM 1.1.3（因爲這個大型項目的限制），但我也使用JDOM 2.0.6進行了嘗試。
@Test
public void buildDTD2()
throws IOException, JDOMException
{
final PathMatchingResourcePatternResolver pmrpr = new PathMatchingResourcePatternResolver();
final File file = pmrpr.getResource("daisy/mathmldtdtemplate.xml").getFile();
final String uri = file.toURI().toString();
final InputStream stream = new BufferedInputStream(new FileInputStream(file));
final SAXBuilder saxBuilder = new SAXBuilder();
saxBuilder.setValidation(true);
saxBuilder.setFeature("http://apache.org/xml/features/validation/schema", true);
final InputSource source = new InputSource(new BufferedInputStream(stream));
source.setSystemId(uri);
final Document doc = saxBuilder.build(source);
String xml2 = new XMLOutputter().outputString(doc);
System.out.println(xml2);
System.out.println("Internal Subset: " + doc.getDocType().getInternalSubset());
}
當我使用System.out.println到最後一行打印出來getInternalSubset()，沒有打印。當我打印出整個文檔時，我會得到：
<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE dtbook PUBLIC "-//NISO//DTD dtbook 2005-2//EN" "http://www.daisy.org/z3986/2005/dtbook-2005-2.dtd">
<dtbook xmlns="http://www.daisy.org/z3986/2005/dtbook/" xmlns:m="http://www.w3.org/1998/Math/MathML" version="2005-2" xml:lang="eng">
<head />
<book>
<frontmatter><doctitle /></frontmatter>
<bodymatter>
<level1>
<p>Test</p>
<m:math xmlns:dtbook="http://www.daisy.org/z3986/2005/dtbook/" id="math0001" dtbook:smilref="nativemathml.smil#math0001" altimg="nativemathml0001.png" alttext="sigma-summation UnderScript i equals zero OverScript infinity EndScripts x Subscript i" overflow="scroll">
<m:mrow>
<m:mstyle displaystyle="true">
<m:munderover>
<m:mo>∑</m:mo>
<m:mrow>
<m:mi>i</m:mi>
<m:mo>=</m:mo>
<m:mn>0</m:mn>
</m:mrow>
<m:mi>∞</m:mi>
</m:munderover>
<m:mrow>
<m:msub>
<m:mi>x</m:mi>
<m:mi>i</m:mi>
</m:msub>
</m:mrow>
</m:mstyle>
</m:mrow>
</m:math>
</level1>
</bodymatter>
<rearmatter><level1><p /></level1></rearmatter>
</book>
</dtbook>
ENTITY定義消失了！我錯過了一些可以讓我維護它們的選項嗎？我該如何維護它們？當我們處理這些文件時，我們可能需要將它們讀入並寫出來，而不會丟失這個DTD。