转换前: <Head><name>wangjj</name><age>23</age></Head>
转换后: 

<?xml version="1.0" encoding="gb2312"?>
<Head>
   <name>wangjj</name>
   <age>23</age>
 </Head>

代码: 

package com.sun.ATest;
import java.io.StringWriter;
import org.dom4j.Document;
 import org.dom4j.DocumentHelper;
 import org.dom4j.io.OutputFormat;
 import org.dom4j.io.XMLWriter;public class XmlFormat {
    //字符串 XML 格式化处理
  public static void main(String[] args) {
   // TODO Auto-generated method stub
   try {
    String temp = new XmlFormat().formatXml("<Head><name>wangjj</name><age>23</age></Head>");
    System.out.println(temp);
   } catch (Exception e) {
    // TODO Auto-generated catch block
    e.printStackTrace();
   }
  } public static String formatXml(String str) throws Exception {
   Document document = null;
   document = DocumentHelper.parseText(str);
   // 格式化输出格式
   OutputFormat format = OutputFormat.createPrettyPrint();
   format.setEncoding("gb2312");
   StringWriter writer = new StringWriter();
   // 格式化输出流
   XMLWriter xmlWriter = new XMLWriter(writer, format);
   // 将document写入到输出流
   xmlWriter.write(document);
   xmlWriter.close();   return writer.toString();
  }
 }