Dom4j实例解析

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。

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 = "<person> <name>James</name> </person>";
        Document document = DocumentHelper.parseText(text);