Java SAX解析XML
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SAX解析XML采用的是从上而下的基于事件驱动的解析方式,在解析过程中会视情况自动调用startDocument()、startElement()、characters()、endElement()、endDocument()等相关的方法。
由编译执行的结果来看:
- startDocument()方法只会在文档开始解析的时候被调用,每次解析只会调用一次。
- startElement()方法每次在开始解析一个元素,即遇到元素标签开始的时候都会调用。
- characters()方法也是在每次解析到元素标签携带的内容时都会调用,即使该元素标签的内容为空或换行。而且如果元素内嵌套元素,在父元素结束标签前, characters()方法会再次被调用,此处需要注意。
- endElement()方法每次在结束解析一个元素,即遇到元素标签结束的时候都会调用。
- endDocument() startDocument()方法只会在文档解析结束的时候被调用,每次解析只会调用一次。
oracle官方解析教程 http://docs.oracle.com/javase/tutorial/jaxp/sax/parsing.html
package com.demo.test;import java.io.FileInputStream;import java.io.FileNotFoundException;import java.io.FileOutputStream;import java.io.IOException;import javax.xml.parsers.ParserConfigurationException;import javax.xml.parsers.SAXParser;import javax.xml.parsers.SAXParserFactory;import javax.xml.transform.OutputKeys;import javax.xml.transform.Result;import javax.xml.transform.Transformer;import javax.xml.transform.TransformerConfigurationException;import javax.xml.transform.sax.SAXTransformerFactory;import javax.xml.transform.sax.TransformerHandler;import javax.xml.transform.stream.StreamResult;import org.xml.sax.Attributes;import org.xml.sax.InputSource;import org.xml.sax.SAXException;import org.xml.sax.helpers.AttributesImpl;import org.xml.sax.helpers.DefaultHandler;public class XmlDemo { private static class SAXHandler extends DefaultHandler { @Override public void startDocument() throws SAXException { System.out.println("startDocument"); } @Override public void endDocument() throws SAXException { System.out.println("endDocument"); } @Override public void startElement(String uri, String localName, String qName, Attributes attributes) throws SAXException { System.out.println("startElement, uri=" + uri + ", localName=" + localName + ", qName=" + qName + ", attributes.getLength()=" + attributes.getLength()); if (attributes.getLength() > 0) { for (int i = 0; i < attributes.getLength(); i++) { System.out.println("startElement attributes(" + i + "): " + attributes.getQName(i) + "=" + attributes.getValue(i)); } } } @Override public void endElement(String uri, String localName, String qName) throws SAXException { System.out.println("endElement, uri=" + uri + ", localName=" + localName + ", qName=" + qName); } @Override public void characters(char[] ch, int start, int length) throws SAXException { System.out.println("characters, start=" + start + ", length=" + length + ", ch=" + new String(ch, start, length)); } } private static void parseXml(String xmlPath) { SAXParserFactory saxParserFactory = SAXParserFactory.newInstance(); FileInputStream fis = null; try { fis = new FileInputStream(xmlPath); InputSource is = new InputSource(fis); // SAX会自动从流中检测正确的字符编码,但是如果流中没有明确指定编码,可能会导致转换错误 is.setEncoding("UTF-8"); SAXParser saxParser = saxParserFactory.newSAXParser(); saxParser.parse(is, new SAXHandler()); } catch (FileNotFoundException e) { e.printStackTrace(); } catch (ParserConfigurationException e) { e.printStackTrace(); } catch (SAXException e) { e.printStackTrace(); } catch (IOException e) { e.printStackTrace(); } finally { if (fis != null) { try { fis.close(); } catch (IOException e) { e.printStackTrace(); } } } } private static void generateXml(String filePath) { SAXTransformerFactory saxTransformerFactory = (SAXTransformerFactory) SAXTransformerFactory.newInstance(); FileOutputStream fos = null; try { TransformerHandler transformerHandler = saxTransformerFactory.newTransformerHandler(); Transformer transformer = transformerHandler.getTransformer(); transformer.setOutputProperty(OutputKeys.ENCODING, "UTF-8"); // 如果是yes,那么会自动换行但不会缩进;如果是no,则不会换行。默认是no// transformer.setOutputProperty(OutputKeys.INDENT, "no"); //不省略的话,会自动添加<?xml version="1.0" encoding="UTF-8"?>。默认是no transformer.setOutputProperty(OutputKeys.OMIT_XML_DECLARATION, "no"); fos = new FileOutputStream(filePath); Result result = new StreamResult(fos); transformerHandler.setResult(result); transformerHandler.startDocument(); AttributesImpl attr = new AttributesImpl(); attr.addAttribute(null, null, "class", String.class.getName(), "value"); startElement(transformerHandler, "html", null); startElement(transformerHandler, "head", null); endElement(transformerHandler, "head"); startElement(transformerHandler, "body", null); selfEndElement(transformerHandler, "p", attr, "characters"); endElement(transformerHandler, "body"); endElement(transformerHandler, "html"); transformerHandler.endDocument(); } catch (FileNotFoundException e) { e.printStackTrace(); } catch (TransformerConfigurationException e) { e.printStackTrace(); } catch (SAXException e) { e.printStackTrace(); } finally { if (fos != null) { try { fos.close(); } catch (IOException e) { e.printStackTrace(); } } } } // SAX默认不自动缩进,因此需要手动根据元素层次进行缩进控制 private static int indent = 0; private static String uri = "http://www.chy.uri"; private static String localname = "localname";// private static String uri = null;// private static String localname = null; private static void startElement(TransformerHandler transformerHandler, String qName, Attributes atts) throws SAXException { System.out.println("startElement " + qName); indent++; addTabs(transformerHandler); transformerHandler.startElement(uri, localname, qName, atts); } private static void endElement(TransformerHandler transformerHandler, String qName) throws SAXException { System.out.println("endElement " + qName); addTabs(transformerHandler); indent--; transformerHandler.endElement(uri, localname, qName); } /** * 自封闭式标签 */ private static void selfEndElement(TransformerHandler transformerHandler, String qName, Attributes atts, String str) throws SAXException { System.out.println("endElement " + qName); indent++; addTabs(transformerHandler); indent--; transformerHandler.startElement(uri, localname, qName, atts); if (str != null) { char[] charArr = str.toCharArray(); transformerHandler.characters(charArr, 0, charArr.length); } transformerHandler.endElement(uri, localname, qName); } /** * SAX不会添加缩进,要自己添加 */ private static void addTabs(TransformerHandler transformerHandler) throws SAXException { System.out.println("addTabs " + indent); char[] ch = new char[indent]; ch[0] = '\n'; if (indent > 1) { for (int i = 1; i < ch.length; i++) { ch[i] = '\t'; } } transformerHandler.characters(ch, 0, ch.length); } public static void main(String[] args) { String xmlPath = "test.xml"; parseXml(xmlPath); generateXml("test.xml"); }}
生成的XML如下
<?xml version="1.0" encoding="UTF-8"?><html xmlns="http://www.chy.uri"> <head> </head> <body> <p class="value">characters</p> </body></html>
这里如果uri变量设置为空,会自动生成一个无结束标签的META标签,并且indent设置为no也无效,还是会自动换行
<?xml version="1.0" encoding="UTF-8"?><html><head><META http-equiv="Content-Type" content="text/html; charset=UTF-8"></head><body><p class="value">characters</p></body></html>
右击项目 –> Properties(Alt + Enter)–> Java Build Path –> Libraries –> 双击JRE System Library
注意:这里如果选择OSGi/Minimum-1.2是找不到”javax.xml.“或”org.xml.sax.”的相关包的。最低版本必须是J2SE-1.5。
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