Java 13 DocumentBuilder 在解析 DTD 文件以验证时中断 HTML

Question

我正在开发使用 DocumentBuilder 解析旧 HTML 文件的程序，以便对其进行相应处理。在这个 HTML 文件中，我们有以下

<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">

这是执行读取的代码片段：

DocumentBuilderFactory documentBuilderFactory;
DocumentBuilder documentBuilder;

documentBuilderFactory = DocumentBuilderFactory.newInstance();
documentBuilder = documentBuilderFactory.newDocumentBuilder();

Document doc = documentBuilder.parse(htmlSource);

随后解析失败并出现以下错误：

Error 1:    The declaration for the entity "HTML.Version" must end with '>'.
      Column Number:    3
      System Identifer: null
      toString:         org.xml.sax.SAXParseException; lineNumber: 31; columnNumber: 3; The declaration for the entity "HTML.Version" must end with '>'.
      Line Number:      31
      Public Identifer: null
      Caused By:

      The declaration for the entity "HTML.Version" must end with '>'.
      Trace Follows:

org.xml.sax.SAXParseException; lineNumber: 31; columnNumber: 3; The declaration for the entity "HTML.Version" must end with '>'.
        at java.xml/com.sun.org.apache.xerces.internal.util.ErrorHandlerWrapper.createSAXParseException(ErrorHandlerWrapper.java:204)
        at java.xml/com.sun.org.apache.xerces.internal.util.ErrorHandlerWrapper.fatalError(ErrorHandlerWrapper.java:178)
        at java.xml/com.sun.org.apache.xerces.internal.impl.XMLErrorReporter.reportError(XMLErrorReporter.java:400)
        at java.xml/com.sun.org.apache.xerces.internal.impl.XMLErrorReporter.reportError(XMLErrorReporter.java:327)
        at java.xml/com.sun.org.apache.xerces.internal.impl.XMLScanner.reportFatalError(XMLScanner.java:1471)
        at java.xml/com.sun.org.apache.xerces.internal.impl.XMLDTDScannerImpl.scanEntityDecl(XMLDTDScannerImpl.java:1597)
        at java.xml/com.sun.org.apache.xerces.internal.impl.XMLDTDScannerImpl.scanDecls(XMLDTDScannerImpl.java:2021)
        at java.xml/com.sun.org.apache.xerces.internal.impl.XMLDTDScannerImpl.scanDTDExternalSubset(XMLDTDScannerImpl.java:299)
        at java.xml/com.sun.org.apache.xerces.internal.impl.XMLDocumentScannerImpl$DTDDriver.dispatch(XMLDocumentScannerImpl.java:1165)
        at java.xml/com.sun.org.apache.xerces.internal.impl.XMLDocumentScannerImpl$DTDDriver.next(XMLDocumentScannerImpl.java:1040)
        at java.xml/com.sun.org.apache.xerces.internal.impl.XMLDocumentScannerImpl$PrologDriver.next(XMLDocumentScannerImpl.java:943)
        at java.xml/com.sun.org.apache.xerces.internal.impl.XMLDocumentScannerImpl.next(XMLDocumentScannerImpl.java:605)
        at java.xml/com.sun.org.apache.xerces.internal.impl.XMLDocumentFragmentScannerImpl.scanDocument(XMLDocumentFragmentScannerImpl.java:541)
        at java.xml/com.sun.org.apache.xerces.internal.parsers.XML11Configuration.parse(XML11Configuration.java:888)
        at java.xml/com.sun.org.apache.xerces.internal.parsers.XML11Configuration.parse(XML11Configuration.java:824)
        at java.xml/com.sun.org.apache.xerces.internal.parsers.XMLParser.parse(XMLParser.java:141)
        at java.xml/com.sun.org.apache.xerces.internal.parsers.DOMParser.parse(DOMParser.java:246)
        at java.xml/com.sun.org.apache.xerces.internal.jaxp.DocumentBuilderImpl.parse(DocumentBuilderImpl.java:339)
        at com.rockwellcollins.ana.xml.XmlParser.parse(XmlParser.java:490)
        at com.rockwellcollins.ana.xml.XmlParser.parse(XmlParser.java:592)
        at com.rockwellcollins.qimt.doorsmapper.doorsmapper.HtmlParser.parseHtml(HtmlParser.java:301)
        at com.rockwellcollins.qimt.doorsmapper.doorsmapper.DoorsMapper.applicationSpecificDoIt(DoorsMapper.java:232)
        at com.rockwellcollins.application.common.ApplicationBase.doIt(ApplicationBase.java:795)
        at com.rockwellcollins.qimt.doorsmapper.doorsmapper.DoorsMapper.main(DoorsMapper.java:300)

它抱怨 DTD 文件的这一部分：

<!ENTITY % HTML.Version "-//W3C//DTD HTML 4.01 Transitional//EN"
  -- Typical usage:

    <!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN"
            "http://www.w3.org/TR/html4/loose.dtd">
    <html>
    <head>
    ...
    </head>
    <body>
    ...
    </body>
    </html>

    The URI used as a system identifier with the public identifier allows
    the user agent to download the DTD and entity sets as needed.

    The FPI for the Strict HTML 4.01 DTD is:

        "-//W3C//DTD HTML 4.01//EN"

    This version of the strict DTD is:

        http://www.w3.org/TR/1999/REC-html401-19991224/strict.dtd

    Authors should use the Strict DTD unless they need the
    presentation control for user agents that don't (adequately)
    support style sheets.

    If you are writing a document that includes frames, use 
    the following FPI:

        "-//W3C//DTD HTML 4.01 Frameset//EN"

    This version of the frameset DTD is:

        http://www.w3.org/TR/1999/REC-html401-19991224/frameset.dtd

    Use the following (relative) URIs to refer to 
    the DTDs and entity definitions of this specification:

    "strict.dtd"
    "loose.dtd"
    "frameset.dtd"
    "HTMLlat1.ent"
    "HTMLsymbol.ent"
    "HTMLspecial.ent"

-->

根据我的初步调查，它抱怨标签中的 -- 评论。如果我删除它们，那么第一个错误就会消失并移至下一个错误。我的问题是，为什么 DocumentBuilder 无法正确读取 DTD 文件？

要添加一些东西，我们无法从 HTML 文件中删除 DTD，因为提供的 HTML 是 HTML 4 特定的，没有它，解析将失败，因为HTML 4 格式。

Answer 1

HTML 4.01 是一个 SGML DTD（XML 是 SGML 的一个子集）并且 HTML 无法使用XML 解析器。与 XML 相比，SGML 中的注释语法允许注释在任何地方和多次出现在标记声明中，这是对的。例如，以下是有效的 SGML 元素声明：

<!ELEMENT e - - (#PCDATA)
  -- declaration for e --
  -- ... other comment -->

该声明还暗示了 SGML 的 XML 子集不支持的功能之一（但解析 HTML 需要），即 标签推断（标签遗漏）。元素名称 e 后的 - O 序列表示 e 允许省略结束元素标记（"O"，如字母 O）但不允许省略起始元素（“-”连字符减号）。 XML 不支持的其他所需功能是 SGML/HTML-style 空元素，例如 img（没有结束元素标记）和属性最小化（如 <div hidden>）。

Java 13 DocumentBuilder 在解析 DTD 文件以验证时中断 HTML

Java 13 DocumentBuilder breaks when parsing DTD file to validate HTML

html

java

xml

dtd

xml-parsing