想通过Jdom向web.xml文件添加servlet的配置信息。如：
<servlet>
        <servlet-name>xxx</servlet-name>
        <servlet-class>com.sdt.action.xxx</servlet-class>
</servlet>
<servlet-mapping>
        <servlet-name>xxx</servlet-name>
        <url-pattern>/xxx</url-pattern>
</servlet-mapping>
但是总是报这样的错误：Exception in thread "main" org.jdom.IllegalAddException: The Content already has an existing parent "servlet"
我的代码如下：

import java.io.File;
import java.io.FileOutputStream;
import org.jdom.Document;
import org.jdom.Element;
import org.jdom.Parent;
import org.jdom.input.SAXBuilder;
import org.jdom.output.XMLOutputter;


/**向web.xml中增加Servlet配置
 *
 * @author liujia
 */
public class DomUtil {
    
    public static void add(String tableName) throws Exception {
        String className = "PersonServlet" ;
        String servletPackage = "com.sdt.servlet" ;
        
        String fileName = "d:/netbeans/workday01/src/test/javaeye/web.xml" ;
        File f = new File(fileName) ;
        SAXBuilder builder = new SAXBuilder() ;
        Document doc = builder.build(f) ;
        Element root = doc.getRootElement() ;
        System.out.println("root: " + root.getName());
        Element servlet = new Element("servlet") ;
        Element servletMapping = new Element("servlet-mapping") ;
        Element servletName = new Element("servletName") ;
        Element servletClass = new Element("servletClass") ;
        Element urlPattern = new Element("urlPattern") ;
        
        servletClass.setText(servletPackage + "." + className) ;
        servletName.setText("className") ;
        urlPattern.setText("/" + className) ;
        
        servlet.addContent(servletName) ;
        servlet.addContent(servletClass) ;
        servletMapping.addContent(servletName) ;
        servletMapping.addContent(urlPattern) ;
        
        Parent p = root.getParent();
        p.removeContent(root);
        root.addContent(servlet) ;
        root.addContent(servletMapping) ;
        
        XMLOutputter out = new XMLOutputter() ;
        out.setFormat(out.getFormat().setEncoding("GBK")) ;
        out.output(doc, new FileOutputStream(new File(fileName),true)) ;
        
    }
    
    
    public static void main(String[] args) throws Exception {
        add("t_person") ;
    }
}

希望大家能帮帮我，实在是解决不了了。