读取xml文件时不做validation的方法

今天遇到一个问题，我使用dom4j读取一个xml文件的内容，该xml文件中指定了一个dtd文件，而我并没有这个dtd文
件，在我用SAXReader读取xml文件时，便报如下错误：

java.io.FileNotFoundException: [dtd文件名] (The system cannot find the file specified)
	at java.io.FileInputStream.open(Native Method)
	at java.io.FileInputStream.(FileInputStream.java:106)
	at java.io.FileInputStream.(FileInputStream.java:66)
	at sun.net.www.protocol.file.FileURLConnection.connect(FileURLConnection.java:70)
	at sun.net.www.protocol.file.FileURLConnection.getInputStream(FileURLConnection.java:161)
	at com.sun.org.apache.xerces.internal.impl.XMLEntityManager.setupCurrentEntity(XMLEntityManager.java:653)
	at com.sun.org.apache.xerces.internal.impl.XMLEntityManager.startEntity(XMLEntityManager.java:1315)
	at com.sun.org.apache.xerces.internal.impl.XMLEntityManager.startDTDEntity(XMLEntityManager.java:1282)
	at com.sun.org.apache.xerces.internal.impl.XMLDTDScannerImpl.setInputSource(XMLDTDScannerImpl.java:283)
	at com.sun.org.apache.xerces.internal.impl.XMLDocumentScannerImpl$DTDDriver.dispatch(XMLDocumentScannerImpl.java:1192)
	at com.sun.org.apache.xerces.internal.impl.XMLDocumentScannerImpl$DTDDriver.next(XMLDocumentScannerImpl.java:1089)
	at com.sun.org.apache.xerces.internal.impl.XMLDocumentScannerImpl$PrologDriver.next(XMLDocumentScannerImpl.java:1002)
	at com.sun.org.apache.xerces.internal.impl.XMLDocumentScannerImpl.next(XMLDocumentScannerImpl.java:648)
	at com.sun.org.apache.xerces.internal.impl.XMLNSDocumentScannerImpl.next(XMLNSDocumentScannerImpl.java:140)
	at com.sun.org.apache.xerces.internal.impl.XMLDocumentFragmentScannerImpl.scanDocument(XMLDocumentFragmentScannerImpl.java:510)
	at com.sun.org.apache.xerces.internal.parsers.XML11Configuration.parse(XML11Configuration.java:807)
	at com.sun.org.apache.xerces.internal.parsers.XML11Configuration.parse(XML11Configuration.java:737)
	at com.sun.org.apache.xerces.internal.parsers.XMLParser.parse(XMLParser.java:107)
	at com.sun.org.apache.xerces.internal.parsers.AbstractSAXParser.parse(AbstractSAXParser.java:1205)
	at com.sun.org.apache.xerces.internal.jaxp.SAXParserImpl$JAXPSAXParser.parse(SAXParserImpl.java:522)
	at org.dom4j.io.SAXReader.read(SAXReader.java:465)
	at org.dom4j.io.SAXReader.read(SAXReader.java:321)

看来，是xerces自动进行了语法检查，其实这个xml文件是合法的，我这是想读取其中一些数据，并不想做validation，而
且我也不能删除xml中的对dtd的引用，我想，只要关闭默认的语法检查就可以了。查了查dom4j的文档，我把能想到的设置
都关闭了：

	reader.setValidation(false);
	reader.setIncludeInternalDTDDeclarations(false);
	reader.setIncludeExternalDTDDeclarations(false);
	reader.setFeature("http://apache.org/xml/features/validation", false);

可是，仍然不行，没办法，只好跟踪源码了，最后在xerces的XMLDocumentScannerImpl里发现了这段代码：

	if (((fValidation || fLoadExternalDTD) 
		&& (fValidationManager == null || !fValidationManager.isCachedDTD()))) {
		// This handles the case of a DOCTYPE that had neither an internal subset or an external subset.
		fDTDScanner.setInputSource(fExternalSubsetSource);
		fExternalSubsetSource = null;
		if (!fDisallowDoctype)
			setScannerState(SCANNER_STATE_DTD_EXTERNAL_DECLS);
		else
			setScannerState(SCANNER_STATE_PROLOG);
		setDriver(fContentDriver);
		if(fDTDDriver == null)
			fDTDDriver = new DTDDriver();
		return fDTDDriver.next();
	}

需要把fValidation和fLoadExternalDTD都设成false才行，继续研究代码，最后终于找到了解决办法：

	SAXReader reader = new SAXReader(false);
	reader.setValidation(false);
	reader.setFeature("http://apache.org/xml/features/nonvalidating/load-external-dtd", false);
	Document document = reader.read(xmlFile);

其中setValidation(false);可以将fValidation设置成false，setFeature("http://apache.org/xml/features/
nonvalidating/load-external-dtd", false);将fLoadExternalDTD设置成false。

希望对其他遇到同样问题的人有些帮助。