HTML转PDF - Java / Java EE

各位大哥大街们，我想把HTML转换成PDF，使用的是FOP，但是报错：
java.lang.ClassCastException: org.apache.fop.layout.BlockArea cannot be cast to org.apache.fop.layout.AreaContainer
at com.test.Html2Pdf.fo2PDF(Html2Pdf.java:115)
115是driver.run()。程序代码如下：
Java code:

package com.test;

import java.io.ByteArrayOutputStream;
import java.io.File;
import java.io.FileInputStream;
import java.io.FileOutputStream;
import java.io.OutputStream;

import javax.xml.parsers.DocumentBuilder;
import javax.xml.parsers.DocumentBuilderFactory;
import javax.xml.transform.Transformer;
import javax.xml.transform.TransformerFactory;
import javax.xml.transform.dom.DOMResult;
import javax.xml.transform.dom.DOMSource;

import org.apache.avalon.framework.logger.ConsoleLogger;
import org.apache.avalon.framework.logger.Logger;
import org.apache.fop.apps.Driver;
import org.apache.fop.tools.DocumentInputSource;
import org.w3c.dom.Document;
import org.w3c.tidy.Tidy;

/*
* Class that converts HTML to PDF using
* the DOM interfaces of JTidy, Xalan, and FOP.
*
* @author N. Afshartous
*
*/
public class Html2Pdf {

public static void main(String[] args) {

// open file
// if (args.length != 2) {
// System.out.println("Usage: Html2Pdf htmlFile styleSheet");
// System.exit(1);
//