Java核心技术II读书笔记（三）

ch2 XML

SAX解析器

SAXParserFactory factory = SAXParserFactory.newInstance();

SAXParser parser = factory.newSAXParser();    //建立SAX解析器对象

parser.parse(source,handler);  //source可以是文件，URL或者字符串输入流，handle是DefaultHandler的子类

DefaultHandler handler = new
    DefaultHandler(){
         public void startElement(String namespaceURI,String lname,String qname, Attributes attrs) throws SAXException{
              if(lname.equalsIngoreCase("a")&&attrs!=null){
                  for(int i=0;i<attrs.getLength();i++){
                       String aname = attrs.getLocalName(i);
                       if(aname.equalsIgnoreCase("href"))
                           System.out.println(attrs.getValue(i));
                  }
              }
         }
    };        

其中qname参数是prefix:localname这种形式。如果命名空间处理特性打开，那么namespaceURI和lname描述的就是命名空间和本地（非限定）名。
与DOM一样，命名空间默认是关闭的，调用工厂类的setNamespaceAware方法激活：

SAXParserFactory factory = SAXParserFactory.newInstnce();

factory.setNamespaceAware(true);

SAXParser saxParser = factory.newSAXParser();

备注：XHTML文件总是以一个DTD引用标签开头，W3C也不情愿提供千万亿次的下载，如果自己不需要验证文件，只需调用：

factory.setFeature("http://apache.org/xml/features/nonvalidating/load-external-dtd",false);

StAX解析器

3 import java.io.*;
4 import java.net.*;
5 import javax.xml.parsers.*;
6 import org.xml.sax.*;
7 import org.xml.sax.helpers.*;
89
/**
10 * This program demonstrates how to use a SAX parser. The program prints all hyperlinks of an
11 * XHTML web page.<br>
12 * Usage: java SAXTest url
13 * @version 1.00 2001-09-29
14 * @author Cay Horstmann
15 */
16 public class SAXTest
17 {
18 public static void main(String[] args) throws Exception
19 {
20     String url;
21     if (args.length == 0)
22     {
23          url = "http://www.w3c.org";
24          System.out.println("Using " + url);
25     }
26     else url = args[0];
27
28     DefaultHandler handler = new DefaultHandler()
29     {
30         public void startElement(String namespaceURI, String lname, String qname,
31 Attributes attrs)
32         {
33              if (lname.equals("a") && attrs != null)
34              {
35                  for (int i = 0; i < attrs.getLength(); i++)
36                  {
37                      String aname = attrs.getLocalName(i);
38                      if (aname.equals("href")) System.out.println(attrs.getValue(i));
39                      }
40                  }
41              }
42          };
43
44          SAXParserFactory factory = SAXParserFactory.newInstance();
45          factory.setNamespaceAware(true);
46          factory.setFeature("http://apache.org/xml/features/nonvalidating/load-external-dtd",
false);
47          SAXParser saxParser = factory.newSAXParser();
48          InputStream in = new URL(url).openStream();
49          saxParser.parse(in, handler);
50   }
51 }

生成XML

不带命名空间的文档：

Document doc = builder.newDocument();  //创建一个空文档

Element rootElement = doc.createElement(rootName);  //创建文档元素

Element childElement = doc.createElement(childName);

Text textNode = doc.createTextNode(textContents);  //创建文本节点

doc.appendChild(rootElement);   //创建跟节点

rootElement.appendChild(childElement);  //创建子节点

childElement.appendChild(textNode);   //创建文本值

rootElement.setAttribute(name,value);  //创建元素属性

带命名空间的文档：

DocumentBuilderFactory factory = DocumentBuilderFactory.newInstance();

factory.setNamespaceAware(true);

builder = factory.newDocumentBuilder();

String namespace = "http://www.w3.org/2000/svg";

Element rootElement = doc.createElementNS(namespace,"svg"); //创建文档元素

Element svgElement = doc.createElement(namespace,"svg:svg");  //带命名空间前缀的写法

rootElement.setAttributeNS(namespace,qualifiedName,value);

----------------------------------------------------------------

XML DOM输出
方式1

Transformer t = TransformerFactory.newInstance().newTransformer();   //这玩意干嘛的？从源到结果的转换API

t.setOutputProperty(OutputKeys.DOCTYPE_SYSTEM,systemIdentifier);

t.setOutputProperty(Outputkeys.DOCTYPE_SYSTEM,publicIdentifier);

t.setOutputProperty(OutputKeys.INDENT,"yes");

t.setOutputProperty(OutputKeys.METHOD,"xml");

t.setOutputProperty("{http://xml.apache.org/xslt}indent-amount","2");

t.transform(new DOMSource(doc),new StreamResult(new FileOutputStream(file)));  //执行上面的设置并且输出到文件中

方式2 LSSerializer

DOMImplementation impl = doc.getImplementation();

DOMImplementationLS implLS = (DOMImplementationLS) impl.getFeature("LS","3.0");

LSSerializer ser = implLS.createLSSerializer();

ser.getDomConfig().setParameter("format-pretty-print",true);  //设置空格和换行

String str = ser.writeToString(doc);  //将文档转换为字符串

LSOutput out = implLS.createLSOutput();

out.setEncoding("UTF-8");

out.setByteStream(Files.newOutputStream(path));

ser.write(doc,out);  //将输出写入文件中

方式3 StAX

XMLOutputFactory factory = XMLOutputFactory.newInstance();

XMLStreamWriter writer = factory.createXMLStreamWriter(out);

接着是一系列的按XML顺序从上到下的操作，如：

产生XML文件头  writer.writeStartDocument();

添加子节点  writer.writeStartElement(name);

...