4种xml解析器区别

XML作用：不同应用之间的通信和数据共享
Dom遍历法：对内存消耗大，容易内存溢出
SAX方法：事件驱动模式，缺点 不易操作，很难同时访问多处不同数据，对内存消耗不大，速度快
jdom方法：
dom4j方法：优秀比jdom优秀

Dom遍历法：全部加载内容到内存
DocumentBuilderFactory d=DocumentBuilderFactory.newInstance();
		try {
			DocumentBuilder bu=d.newDocumentBuilder();
			Document dom=bu.parse("pom.xml");
			NodeList nl=dom.getElementsByTagName("dependency");
			System.out.println(nl.getLength());
			for(int i=0;i<nl.getLength();i++) {
				Node node=nl.item(i);
				NodeList nnm=node.getChildNodes();

				for(int k=0;k<nnm.getLength();k++) {
					Node node1=nnm.item(k);
					if(node1.getNodeType()==Node.ELEMENT_NODE) {
						String tt=node1.getNodeName();
						String tt1=node1.getTextContent();
						System.out.println(tt+":"+tt1+"\n");
					}

				}
			}
		} catch (ParserConfigurationException e) {
			// TODO Auto-generated catch block
			e.printStackTrace();
		} catch (SAXException e) {
			// TODO Auto-generated catch block
			e.printStackTrace();
		} catch (IOException e) {
			// TODO Auto-generated catch block
			e.printStackTrace();
		}
	}

SAX方法 两个步骤：
package com.xml;

import org.xml.sax.Attributes;
import org.xml.sax.SAXException;
import org.xml.sax.helpers.DefaultHandler;

public class SAXhandler extends DefaultHandler {
	int index=0;
	public void startElement(String uri, String localName,String qName,Attributes attributes) throws SAXException {
		super.startElement(uri, localName, qName, attributes);
		if(qName=="project") {
			index++;
			System.out.println("开始遍历第"+index+"gejiedian");
			//String va=attributes.getValue("id");//已知属性名称
			int aa=attributes.getLength();
			for(int i=0;i<aa;i++) {
				String name=attributes.getQName(i);
				String va=attributes.getValue(name);
				System.out.println(name+":"+va);
			}
		}else if(qName.equals("dependency")) {
			System.out.print("节点名称："+qName);
		}

	}
	public void endElement(String uri, String localName, String qName) throws SAXException {
		super.endElement(uri, localName, qName);
		if(qName.equals("project")) {
			System.out.println("end遍历第"+index+"gejiedian");
		}

	}
	public void startDocument() throws SAXException {
		super.startDocument();
		System.out.println("解析开始");
	}
	public void endDocument() throws SAXException {
		super.endDocument();
		System.out.println("解析结束");
	}

	public void characters(char[]ch, int start, int length) throws SAXException {
		super.characters(ch, start, length);
		String value=new String(ch, start, length);
		if(!value.trim().equals("")) {
			System.out.println(value);
		}

	}
}

import java.io.IOException;

import javax.xml.parsers.ParserConfigurationException;
import javax.xml.parsers.SAXParser;
import javax.xml.parsers.SAXParserFactory;

import org.xml.sax.SAXException;

public class SAX {

	public static void main(String[] args) {
		// TODO Auto-generated method stub
		SAXParserFactory sf=SAXParserFactory.newInstance();
		try {
			SAXParser sp=sf.newSAXParser();
			SAXhandler sh=new SAXhandler();
			sp.parse("pom.xml", sh);

		} catch (ParserConfigurationException | SAXException e) {
			// TODO Auto-generated catch block
			e.printStackTrace();
		} catch (IOException e) {
			// TODO Auto-generated catch block
			e.printStackTrace();
		}

	}

}

jdom方法：需要额外jar包

import java.io.File;

import java.io.IOException;
import java.util.ArrayList;
import java.util.List;

import org.jdom.Attribute;
import org.jdom.Document;
import org.jdom.Element;
import org.jdom.JDOMException;
import org.jdom.input.SAXBuilder;

public class JDOM {

	public static void main(String[] args) throws JDOMException, IOException {
		SAXBuilder sb=new SAXBuilder();
		Document Document = sb.build(new File("pom1.xml"));
		Element rootelement=Document.getRootElement();
		List<Element> listele=rootelement.getChildren();
		List<Object> lo=new ArrayList<Object>();

		for( Element ele:listele) {
			obj o=new obj();
			System.out.println("开始"+(listele.indexOf(ele)+1)+"个");
			List<Attribute> attrs=ele.getAttributes();
			for(Attribute attr:attrs) {
				String attrname=attr.getName();
				String attrvalue=attr.getValue();
				System.out.println(attrname+":"+attrvalue);
			}
			List<Element> list_sun= ele.getChildren();
			for( Element ele1:list_sun) {

				if(ele1.getName().equals("groupId") ) {
				o.setGroupId(ele1.getValue());
			}else if(ele1.getName().equals("artifactId")) {
				o.setArtifactId(ele1.getValue());
			}
				}
			lo.add(o);
			o=null;

		}

		System.out.println(lo);

	}

}

dom4j方法：
import java.io.File;
import java.util.Iterator;
import java.util.List;

import org.dom4j.Attribute;
import org.dom4j.Document;
import org.dom4j.DocumentException;
import org.dom4j.Element;
import org.dom4j.io.SAXReader;

public class dom4j {

	public static void main(String[] args) throws DocumentException {
		SAXReader sr=new SAXReader();
		Document Document = sr.read(new File("pom1.xml"));
		Element root=Document.getRootElement();
		Iterator it=root.elementIterator();
		while(it.hasNext()) {
			Element ele=(Element) it.next();
			List<Attribute> list=ele.attributes();
			for(Attribute attr:list) {
			System.out.println(attr.getName()+":"+attr.getValue());
			}

			Iterator  suneles=ele.elementIterator();
			while(suneles.hasNext()) {
				Element ele1=(Element) suneles.next();

				System.out.println(ele1.getName()+":"+ele1.getStringValue());
				}

		}
	}

}