Dom4j是一个易于使用的，开源的库，在Java平台上与XML,XPath,XSLT协同工作。使用Java集合框架，全面支持DOM,SAX,JAXP。 
官方网站:http://dom4j.org

1.将XML文件转换为一个Document对象

import java.net.URL;

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

public class Foo {

public Document parse(URL url) throws DocumentException { 
        SAXReader reader = new SAXReader(); 
        Document document = reader.read(url); 
        return document; 
    } 
}

2.很多方法用于操作Document，可以返回标准的Java迭代器

public void bar(Document document) throws DocumentException {

Element root = document.getRootElement();

// iterate through child elements of root 
        for ( Iterator i = root.elementIterator(); i.hasNext(); ) { 
            Element element = (Element) i.next(); 
            // do something 
        }

// iterate through child elements of root with element name "foo" 
        for ( Iterator i = root.elementIterator( "foo" ); i.hasNext(); ) { 
            Element foo = (Element) i.next(); 
            // do something 
        }

// iterate through attributes of root 
        for ( Iterator i = root.attributeIterator(); i.hasNext(); ) { 
            Attribute attribute = (Attribute) i.next(); 
            // do something 
        } 
     }

3.快速循环

如果你需要遍历一个很大的XML文档，可以使用快速循环(递归)来改善性能。可以避免为每一次循环都创建一个迭代器对象。

public void treeWalk(Document document) { 
        treeWalk( document.getRootElement() ); 
    }

public void treeWalk(Element element) { 
        for ( int i = 0, size = element.nodeCount(); i < size; i++ ) { 
            Node node = element.node(i); 
            if ( node instanceof Element ) { 
                treeWalk( (Element) node ); 
            } 
            else { 
                // do something…. 
            } 
        } 
    }

4.创建一个新的XML文档

import org.dom4j.Document; 
import org.dom4j.DocumentHelper; 
import org.dom4j.Element;

public class Foo {

public Document createDocument() { 
        Document document = DocumentHelper.createDocument(); 
        Element root = document.addElement( "root" );

Element author1 = root.addElement( "author" ) 
            .addAttribute( "name", "James" ) 
            .addAttribute( "location", "UK" ) 
            .addText( "James Strachan" ); 
        
        Element author2 = root.addElement( "author" ) 
            .addAttribute( "name", "Bob" ) 
            .addAttribute( "location", "US" ) 
            .addText( "Bob McWhirter" );

return document; 
    } 
}

5.将XML文档写入文件

通过write()方法将一个XML文档写入文件是最简单的方式。 
    FileWriter out = new FileWriter( "foo.xml" ); 
    document.write( out ); 
    
  如果你想改变输出的格式，比如美观的格式（含缩进）和压缩的格式（不含缩进），可以使用XMLWriter类。

import org.dom4j.Document; 
import org.dom4j.io.OutputFormat; 
import org.dom4j.io.XMLWriter;

public class Foo {

public void write(Document document) throws IOException {

// lets write to a file 
        XMLWriter writer = new XMLWriter( 
            new FileWriter( "output.xml" ) 
        ); 
        writer.write( document ); 
        writer.close();

// Pretty print the document to System.out 
        OutputFormat format = OutputFormat.createPrettyPrint(); 
        writer = new XMLWriter( System.out, format ); 
        writer.write( document );

// Compact format to System.out 
        format = OutputFormat.createCompactFormat(); 
        writer = new XMLWriter( System.out, format ); 
        writer.write( document ); 
    } 
}

6.XML和String之间的相互转换

通过asXML()方法，你可以将一个Document,Attribute或Element对象转换成一个包含XML文本的字符串。 
        Document document = …; 
        String text = document.asXML();

同样，通过DocumentHelper.parseText()方法，你也可以方便地将一个字符串形式的XML转换成一个Document对象。 
        String text = " James "; 
        Document document = DocumentHelper.parseText(text);