Html serializer

import java.io.*;
import javax.servlet.http.*;
import javax.servlet.*;
import org.apache.html.dom.*;
import org.apache.xml.serialize.*;

public class AcessoTeste extends HttpServlet {
	public void doGet(HttpServletRequest req, HttpServletResponse res) throws IOException, ServletException{
		HTMLDocumentImpl htmldoc = new HTMLDocumentImpl();
		PrintWriter fos = res.getWriter();
		
		HTMLSerializer serializer = new HTMLSerializer();
		serializer.setOutputCharStream(fos);
		serializer.asDOMSerializer();
		serializer.serialize(htmldoc.getDocumentElement());
	}
}

java.lang.NoClassDefFoundError: Could not initialize class org.apache.xml.serialize.HTMLdtd

org.apache.xml.serialize.HTMLSerializer.serializeElement(Unknown Source)

org.apache.xml.serialize.BaseMarkupSerializer.serializeNode(Unknown Source)

org.apache.xml.serialize.BaseMarkupSerializer.serialize(Unknown Source)

Teste.(Teste.java:48)

AcessoTeste.doGet(AcessoTeste.java:8)

javax.servlet.http.HttpServlet.service(HttpServlet.java:689)

javax.servlet.http.HttpServlet.service(HttpServlet.java:802)

sun.reflect.GeneratedMethodAccessor58.invoke(Unknown Source)

sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25)

java.lang.reflect.Method.invoke(Method.java:597)

org.apache.catalina.security.SecurityUtil$1.run(SecurityUtil.java:244)

java.security.AccessController.doPrivileged(Native Method)

javax.security.auth.Subject.doAsPrivileged(Subject.java:517)

org.apache.catalina.security.SecurityUtil.execute(SecurityUtil.java:276)

org.apache.catalina.security.SecurityUtil.doAsPrivilege(SecurityUtil.java:162)