Java程式在解析xml檔案時，如果xml檔案中指定了dtd，在預設會從指定的url下載dtd檔案，但是很多情況下如果網路連線不上，或者防火牆原因，dtd檔案無法下載下來導致程式報連線超時異常，解析xml失敗。有兩種方法解決該類問題：

1.指定從本地讀取dtd檔案

若要解析的xml檔案中有如下的dtd宣告：。

<!DOCTYPE concept PUBLIC "-//OASIS//DTD DITA Concept//EN" "http://docs.oasis-open.org/dita/v1.2/os/dtd1.2/technicalContent/dtd/concept.dtd">

                上述的dtd宣告中publicId為-//OASIS//DTD DITA Concept//EN

systemId：被引用的外部實體的系統識別符號。

                 上述的dtd宣告中systemId為http://docs.oasis-open.org/dita/v1.2/os/dtd1.2/technicalContent/dtd/concept.dtd

可以通過重新SAX的EntityResolver類的resolveEntity(String publicId, String systemId) throws SAXException, IOException

/**
 * Implementation of <code>org.xml.sax.EntityResolver</code> that loads
 * entitities (for example dtd files) from the classpath.
 */
public class ClasspathEntityResolver
    implements EntityResolver
{

    public InputSource resolveEntity(String publicId, String systemId)
        throws SAXException, IOException
    {
    	
        if (systemId != null)
        {
            
            int index = systemId.lastIndexOf('/');
            if (index != -1)
            {
            	systemId = systemId.substring(index + 1);
            }
            systemId = "/" + systemId;
            InputStream istr = Thread.currentThread().getContextClassLoader().getResourceAsStream(systemId);
            if (istr != null)
            {
                return new InputSource(istr);
            }
        }
        return null;
    }
}
 

SAXParserFactory spf = SAXParserFactory.newInstance();
SAXParser saxParser = spf.newSAXParser();
	    
xmlReader = saxParser.getXMLReader();
xmlReader.setEntityResolver(new ClasspathEntityResolver());
xmlReader.setContentHandler(handler);
try {
	xmlReader.parse(new InputSource(inputFilePath));
	} catch (Exception e) {
		e.printStackTrace();
	}

注意：

<!DOCTYPE concept SYSTEM "http://docs.oasis-open.org/dita/v1.2/os/dtd1.2/technicalContent/dtd/concept.dtd">

<!DOCTYPE concept PUBLIC "-//OASIS//DTD DITA Concept//EN" "http://docs.oasis-open.org/dita/v1.2/os/dtd1.2/technicalContent/dtd/concept.dtd">

2.解析xml檔案時徹底忽略dtd：

SAX解析器可以通過指定http://apache.org/xml/features/nonvalidating/load-external-dtd屬性來確定是否忽略dtd，例子如下：

SAXParserFactory spf = SAXParserFactory.newInstance();
SAXParser saxParser = spf.newSAXParser();
	    
xmlReader = saxParser.getXMLReader();
xmlReader.setFeature("http://apache.org/xml/features/nonvalidating/load-external-dtd", false);
xmlReader.setContentHandler(handler);
try {
	xmlReader.parse(new InputSource(inputFilePath));
	} catch (Exception e) {
		e.printStackTrace();
	}