一、解析XML檔案時，遇到DTD的定義要怎麼辦？

    下面這段程式碼是ibatis配置檔案，用w3c Dom(其實任意一種解析方式都是這樣)都會從http://www.ibatis.com/dtd/sql-map-config-2.dtd  這 個地址找對應的DTD檔案進行校驗，如果因特網上這個地址不存在的話，就會報 java.net.ConnectException: Connection timed out: connect  。

1. <? xml version = "1.0" encoding = "UTF-8" ?>
2. <!DOCTYPE sqlMapConfig PUBLIC "-//iBATIS.com//DTD SQL Map Config 2.0//EN" "http://www.ibatis.com/dtd/sql-map-config-2.dtd">
3. < sqlMapConfig >
4. < settings useStatementNamespaces = "true" />
5. <!--防止空SqlMap報錯 by zhangbo start -->
6. < sqlMap resource = "ibatis/project/project-blank.xml"
   />
7. < sqlMap resource = "ibatis/project/user-mapping.xml" />
8. </ sqlMapConfig >

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE sqlMapConfig PUBLIC "-//iBATIS.com//DTD SQL Map Config 2.0//EN" "http://www.ibatis.com/dtd/sql-map-config-2.dtd">
<sqlMapConfig>
<settings useStatementNamespaces="true"/>
<!--防止空SqlMap報錯 by zhangbo start -->
<sqlMap resource="ibatis/project/project-blank.xml"/>

<sqlMap resource="ibatis/project/user-mapping.xml"/>
</sqlMapConfig>

   遇到這種問題可以有兩種解析方式，第一把DTD下載的本地，指定從本地載入DTD檔案；另一種，乾脆忽略DTD檔案。

這兩種方式都是以重新構建實體的解析器(EntityResolver)為基礎解決方案的，重新構建實體解析器而不是使用預設的實體解析器，因為默 認的解析器會根據實際的url進行讀取，下面是一段如何來解析上面提到的配置檔案，兩種方式都有標註

1. public void  addToIbatisTotleConfig() {  
2.         try  {  
3.             DocumentBuilderFactory factory = DocumentBuilderFactory  
4.                     .newInstance();  
5.             factory.setIgnoringElementContentWhitespace(true );  
6.             DocumentBuilder db = factory.newDocumentBuilder();            
7.             db.setEntityResolver(new  EntityResolver(){  
8.             public  InputSource resolveEntity(String publicId, String systemId)  throws  SAXException, IOException {                  
9.                            if (publicId.equals( "-//iBATIS.com//DTD SQL Map Config 2.0//EN" )){  
10.                               //這是第一種方式，即忽略DTD，新建一個預設的空XML來代替
11.                                return new  InputSource( new  ByteArrayInputStream( "<?xml version='1.0' encoding='GBK'?>" .getBytes()));  
12.                                //這是第二種方式，即指定本地的DTD檔案，當然，這種方式需要把XML檔案下載到本地，放入對應的目錄中
13.                               // InputStream dtd_stream = this.getClass().getResourceAsStream("..//dtd/sql-map-config-2.dtd");
14.                               //    return new InputSource(dtd_stream);
15.                            }                            
16.                     return null ;  
17.                 }});  
18.             String ibatisTotalConfigFileName = ctx.getIbatisTotalConfigFile();  
19.             File ibatisTotalConfigFile = new  File(ibatisTotalConfigFileName);  
20.             Document xmldoc = db.parse("file://localhost//" +ibatisTotalConfigFileName);  
21.             Element root = xmldoc.getDocumentElement();  
22.             } catch  (Exception e) {  
23.             e.printStackTrace();  
24.         }  
25.     }  

public void addToIbatisTotleConfig() {
		try {
			DocumentBuilderFactory factory = DocumentBuilderFactory
					.newInstance();
			
			factory.setIgnoringElementContentWhitespace(true);
			DocumentBuilder db = factory.newDocumentBuilder();			
			db.setEntityResolver(new EntityResolver(){
			public InputSource resolveEntity(String publicId, String systemId) throws SAXException, IOException {				 
				           if(publicId.equals("-//iBATIS.com//DTD SQL Map Config 2.0//EN")){
				        	  //這是第一種方式，即忽略DTD，新建一個預設的空XML來代替
				        	   return new InputSource(new ByteArrayInputStream("<?xml version='1.0' encoding='GBK'?>".getBytes()));
				        	   //這是第二種方式，即指定本地的DTD檔案，當然，這種方式需要把XML檔案下載到本地，放入對應的目錄中
				        	  // InputStream dtd_stream = this.getClass().getResourceAsStream("..//dtd/sql-map-config-2.dtd");
				        	  //    return new InputSource(dtd_stream);

				           }				          
					return null;
				}});
			String ibatisTotalConfigFileName = ctx.getIbatisTotalConfigFile();
			File ibatisTotalConfigFile = new File(ibatisTotalConfigFileName);
			Document xmldoc = db.parse("file://localhost//"+ibatisTotalConfigFileName);
			Element root = xmldoc.getDocumentElement();
			} catch (Exception e) {
			e.printStackTrace();
		}
	}

二、使用W3CDom編輯完上面的XML檔案，把document轉換為XML檔案的時候，DTD定義會丟失，如果要加上，要怎麼辦？

       加DTD定義時，要在轉換器中操作，重點使用這個兩句程式碼：

1. transformer.setOutputProperty(javax.xml.transform.OutputKeys.DOCTYPE_PUBLIC, doc.getDoctype().getPublicId());    
2.           transformer.setOutputProperty(javax.xml.transform.OutputKeys.DOCTYPE_SYSTEM, doc.getDoctype().getSystemId());  

   transformer.setOutputProperty(javax.xml.transform.OutputKeys.DOCTYPE_PUBLIC, doc.getDoctype().getPublicId());  
	            transformer.setOutputProperty(javax.xml.transform.OutputKeys.DOCTYPE_SYSTEM, doc.getDoctype().getSystemId());

DTD定義的值在document物件中是有的，你可以直接輸出，也可以改變。

下面是我的實際應用

1. import  java.io.File;  
2. import  java.io.FileNotFoundException;  
3. import  java.io.FileOutputStream;  
4. import  javax.xml.transform.Transformer;  
5. import  javax.xml.transform.TransformerConfigurationException;  
6. import  javax.xml.transform.TransformerException;  
7. import  javax.xml.transform.TransformerFactory;  
8. import  javax.xml.transform.dom.DOMSource;  
9. import  javax.xml.transform.stream.StreamResult;  
10. import  javax.xml.xpath.XPath;  
11. import  javax.xml.xpath.XPathConstants;  
12. import  javax.xml.xpath.XPathExpressionException;  
13. import  javax.xml.xpath.XPathFactory;  
14. import  org.w3c.dom.Document;  
15. import  org.w3c.dom.Node;       
16. public static void  saveXml(String fileName, Document doc) { // 將Document輸出到檔案   
17.             TransformerFactory transFactory = TransformerFactory.newInstance();     
18.             try  {     
19.                 Transformer transformer = transFactory.newTransformer();     
20.                 transformer.setOutputProperty("indent" ,  "yes" );     
21.                 DOMSource source = new  DOMSource();     
22.                 source.setNode(doc);    
23.                 System.out.println(doc.getDoctype().getPublicId());  
24.                 transformer.setOutputProperty(javax.xml.transform.OutputKeys.DOCTYPE_PUBLIC, doc.getDoctype().getPublicId());    
25.                 transformer.setOutputProperty(javax.xml.transform.OutputKeys.DOCTYPE_SYSTEM, doc.getDoctype().getSystemId());  
26.                 StreamResult result = new  StreamResult();     
27.                 result.setOutputStream(new  FileOutputStream(fileName));     
28.                 transformer.transform(source, result);     
29.             } catch  (TransformerConfigurationException e) {     
30.                 e.printStackTrace();     
31.             } catch  (TransformerException e) {     
32.                 e.printStackTrace();     
33.             } catch  (FileNotFoundException e) {     
34.                 e.printStackTrace();     
35.             }     
36.         }   

import java.io.File;
import java.io.FileNotFoundException;
import java.io.FileOutputStream;

import javax.xml.transform.Transformer;
import javax.xml.transform.TransformerConfigurationException;
import javax.xml.transform.TransformerException;
import javax.xml.transform.TransformerFactory;
import javax.xml.transform.dom.DOMSource;
import javax.xml.transform.stream.StreamResult;
import javax.xml.xpath.XPath;
import javax.xml.xpath.XPathConstants;
import javax.xml.xpath.XPathExpressionException;
import javax.xml.xpath.XPathFactory;

import org.w3c.dom.Document;
import org.w3c.dom.Node;	 



public static void saveXml(String fileName, Document doc) {// 將Document輸出到檔案   
	        TransformerFactory transFactory = TransformerFactory.newInstance();   
	        try {   
	            Transformer transformer = transFactory.newTransformer();   
	            transformer.setOutputProperty("indent", "yes");   
	  
	            DOMSource source = new DOMSource();   
	            source.setNode(doc);  
	            System.out.println(doc.getDoctype().getPublicId());
	             
	            transformer.setOutputProperty(javax.xml.transform.OutputKeys.DOCTYPE_PUBLIC, doc.getDoctype().getPublicId());  
	            transformer.setOutputProperty(javax.xml.transform.OutputKeys.DOCTYPE_SYSTEM, doc.getDoctype().getSystemId());
	            StreamResult result = new StreamResult();   
	            result.setOutputStream(new FileOutputStream(fileName));   
	  
	            transformer.transform(source, result);   
	        } catch (TransformerConfigurationException e) {   
	            e.printStackTrace();   
	        } catch (TransformerException e) {   
	            e.printStackTrace();   
	        } catch (FileNotFoundException e) {   
	            e.printStackTrace();   
	        }   
	    }