Java & xml学习笔记 SAX篇

答案：Java & XML学习笔记
1、需要软件
   java,解析器(例如Xerces),API(例如SAX,DOM)
2、SAX机制
  1)解析
    String xmlURI = "c:/test.xml";
    String vendorParserClass = "org.apache.xerces.parsers.SAXParser";
    XMLReaer reader = XMLReaderFactory.createXMLReader(vendorParserClass);

    InputSource inputSource = new InputSource(xmlURI);
    reader.parse(inputSource);

    这样一个xml文档解析过程就完成了。因为SAX是采用时间处理机制来解析XML
    文档的，在解析过程中会触发一些事件，也就是执行特定的方法，你可以实现
    这些方法，就可以通过解析xml来做一些事情了
  2)处理
    SAX2.0定义的核心处理接口一共有
    org.xml.sax.ContentHandler
    org.xml.sax.ErrorHandler
    org.xml.sax.DTDHandler
    org.xml.sax.EntityResolver
    这些接口是通过
    org.xml.sax.XMLReader的setContentHandler(),setEroorHandler(),
    setDTDHandler(),setEntityHandler()注册到解析器，这里面最重要的是
    org.xml.sax.ContentHandler接口，它具体如下
    public interface ContentHandler{
        public void setDocumentLocator(Locator locator);
 public void startDocument() throws SAXException;
 public void endDocument() throws SAXException;
 public void startPrefixMapping(String prefix,String uri)
        throws SAXException;
 public void endPrefixMapping(String prifix)
        throws SAXException;
 public void startElement(String namespaceURI,String localName,
        String qName,Attributes atts) throws SAXException;
 public void endElement(String namespaceURI,String localName,
        String qName) throws SAXException;
 public void characters(char ch[],int start,int length)
        throws SAXException;
 public void ignorableWhitespace(char ch[],int start,int length)
        throws SAXException;
 public void processingInstruction(String target,String data)
        throws SAXException;
 public void skippedEntity(String name)
        throws SAXException;
    }
    通过setContentHandler()将你实现的ContentHandler注册给XMLReader之后，
    在解析过程中，系统根据各种条件执行接口中的方法，下面简单说明一下
    1)文档定位器
       private Locator locator;

       public void setDocumentLocator(Locator locator){
           this.locator = locator;
       }

       通常情况下，你只要如此实现就可以了，这个主要是得到当前解析的位置，
       通过得到的locator，你可以使用它的getLineNumber(),getColumnName()等
       方法，可以得到文档当前的位置，但要注意的是，这个locator不能保存，只
       针对当前的解析有效
    2)文档的开头和结尾
      public void startDocument() throws SAXException{
         //解析过程中仅位于setDocumentLocator()方法后调用
      }
      public void endDocument() throws SAXException{
         //解析过程中最后调用
      }

      大多数情况下你可以不用理他们，只要写个空方法就可以了
    3)名字空间的开始和结束
      public void startPrefixMapping(String prefix,String uri)
      throws SAXException{
      }
      public void endPrefixMapping(String prifix)
      throws SAXException{
      }
    4)元素的开始和结束
      public void startElement(String namespaceURI,String localName,
      String qName,Attributes atts) throws SAXException{
      }
      public void endElement(String namespaceURI,String localName,
      String qName) throws SAXException{
      }
    5)元素的数据
      public void characters(char ch[],int start,int length)
      throws SAXException{
      String s = new String(ch,start,length);
      }
      这个是得到当前的元素的文本数据
    6)可以忽略的空白
      public void ignorableWhitespace(char ch[],int start,int length)
      throws SAXException{
      }
    7)实体
      public void skippedEntity(String name)
        throws SAXException{
      }
    8)指令处理
      public void processingInstruction(String target,String data)
      throws SAXException{
      }
  3)例子：这个是从Java & XML 中复制过来的，
/*
 * Created on 2004-11-30
 *
 * TODO To change the template for this generated file go to
 * Window - Preferences - Java - Code Style - Code Templates
 */
package javaxml2;

/**
 * @author yuangfang
 *
 * TODO To change the template for this generated type comment go to
 * Window - Preferences - Java - Code Style - Code Templates
 */

import java.io.*;
import java.util.*;
import org.xml.sax.*;
import org.xml.sax.ext.LexicalHandler;
import org.xml.sax.helpers.XMLReaderFactory;

import java.awt.*;
import javax.swing.*;
import javax.swing.tree.*;

public class SAXTreeViewer extends JFrame{
 
 private String vendorParserClass =  "org.apache.xerces.parsers.SAXParser";

 private JTree jTree;
 DefaultTreeModel defaultTreeModel;
 
 public SAXTreeViewer(){
  super("SAX Tree Viewer");
  setSize(600,450);
 }
 
 public void init(String xmlURI) throws IOException,SAXException{
  DefaultMutableTreeNode base = new DefaultMutableTreeNode("XML Document:" + xmlURI);
  defaultTreeModel = new DefaultTreeModel(base);
  jTree = new JTree(defaultTreeModel);
  
  buildTree(defaultTreeModel,base,xmlURI);
  getContentPane().add(new JScrollPane(jTree),BorderLayout.CENTER);
  
 }
 
 public void buildTree(DefaultTreeModel treeModel,DefaultMutableTreeNode base,String xmlURI)
 throws IOException,SAXException{
  
  String featureURI = "";
  try{
   XMLReader reader = XMLReaderFactory.createXMLReader(vendorParserClass);
   
   ContentHandler jTreeContentHandler = new JTreeContentHandler(treeModel,base);
   ErrorHandler jTreeErrorHandler = new JTreeErrorHandler();
   
   reader.setContentHandler(jTreeContentHandler);
   reader.setErrorHandler(jTreeErrorHandler);
   reader.setEntityResolver(new SimpleEntityResolver());
   
   featureURI = "http://xml.org/sax/features/validation";
   reader.setFeature(featureURI,true);
   
   featureURI = "http://xml.org/sax/features/namespaces";
   setNamespaceProcessing(reader,true);
   
   featureURI = "http://xml.org/sax/features/string-interning";
   reader.setFeature(featureURI,true);
   
   featureURI = "http://apache.org/xml/features/validation/schema";
   reader.setFeature(featureURI,false);
   
   InputSource inputSource = new InputSource(xmlURI);
   reader.parse(inputSource);
  }
  catch(SAXNotRecognizedException e){
   System.out.println("The parse class " + vendorParserClass 
     + " does not recognize the feature URI " + featureURI);
   System.exit(0);
  }
  catch(SAXNotSupportedException e){
   System.out.println("The parser class " + vendorParserClass +
     " does not support the feature URI " + featureURI);
  }
 }
 
 private void setNamespaceProcessing(XMLReader reader,boolean state)
 throws SAXNotSupportedException,SAXNotRecognizedException
 {
  reader.setFeature("http://xml.org/sax/features/namespaces",state);
  reader.setFeature("http://xml.org/sax/features/namespace-prefixes",!state);
 }
 public static void main(String[] args) {
  try{
   if(args.length != 1){
    System.out.println("Usage:Java javaxml2.SAXTreeViewer " + "[XML Document URI]");
    System.exit(0);
   }
   SAXTreeViewer viewer = new SAXTreeViewer();
   viewer.init(args[0]);
   viewer.setVisible(true);
  }catch(Exception e)
  {
   e.printStackTrace();
  }
 }
}

class JTreeContentHandler implements ContentHandler,LexicalHandler{
 private DefaultTreeModel treeModel;
 
 private DefaultMutableTreeNode current;
 
 private Locator locator;
 
 private Map namespaceMappings;
 
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