核心代码：

package com.ddatsh; import java.io.IOException;import java.io.StringReader;import java.io.StringWriter;import java.io.UnsupportedEncodingException; import org.dom4j.Document;import org.dom4j.DocumentException;import org.dom4j.io.OutputFormat;import org.dom4j.io.SAXReader;import org.dom4j.io.XMLWriter; public class XmlFormat { public static String format(String str) throws Exception { SAXReader reader = new SAXReader(); // System.out.println(reader); // 注释：创建一个串的字符输入流 StringReader in = new StringReader(str); Document doc = reader.read(in); // System.out.println(doc.getRootElement()); // 注释：创建输出格式 OutputFormat formater = OutputFormat.createPrettyPrint(); //formater=OutputFormat.createCompactFormat(); // 注释：设置xml的输出编码 formater.setEncoding("utf-8"); // 注释：创建输出(目标) StringWriter out = new StringWriter(); // 注释：创建输出流 XMLWriter writer = new XMLWriter(out, formater); // 注释：输出格式化的串到目标中，执行后。格式化后的串保存在out中。 writer.write(doc); writer.close(); System.out.println(out.toString()); // 注释：返回我们格式化后的结果 return out.toString(); } public static void main(String[] args) throws Exception { String head="<?xml version=\"1.0\" encoding=\"GBK\"?>"; String str = "<RequestData><HeadData><UserCode>sh1_admin</UserCode><UserName>sh1_admin</UserName><UserCompanyCode>3107</UserCompanyCode><UserCompanyName>上海分公司一部</UserCompanyName><RequestType>03</RequestType></HeadData><BodyData><ReportId>113100000033</ReportId><Insurant>a5rfg87</Insurant><NumberPlate>沪E78612</NumberPlate><EngineModel></EngineModel><CarVin></CarVin><AccidentDate>2011-02-25 15:07:00</AccidentDate><ReportDate>2011-02-25 15:07:00</ReportDate><Province>310000</Province><City>310100</City><District></District><AccidentPlace>1</AccidentPlace><AccidentLongitude></AccidentLongitude><AccidentLatitude></AccidentLatitude><SurveyLongitude></SurveyLongitude><SurveyLatitude></SurveyLatitude><SceneReportFlag></SceneReportFlag><Reporter></Reporter><ReporterTel></ReporterTel><SurveyPlace></SurveyPlace><OperatorId>3525</OperatorId><OperatorName>sh_admin</OperatorName><ReportDealId>30000800</ReportDealId><ReportDealName>江苏分公司</ReportDealName><CompanyName></CompanyName><CustomerTypeCode></CustomerTypeCode><ForcePolicyId>a5rfg87a5rfg87a5rfg87</ForcePolicyId><BizPolicyId></BizPolicyId><Index>0</Index><FieldName>5</FieldName></BodyData></RequestData>"; // System.out.println(str); format(str); } }

oschina用的在线格式化xml的工具就是使用此段代码。