servlet导出pdf

import java.io.ByteArrayOutputStream;
import java.io.IOException;

import javax.servlet.ServletException;
import javax.servlet.ServletOutputStream;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

import com.itextpdf.text.Document;
import com.itextpdf.text.DocumentException;
import com.itextpdf.text.Paragraph;
import com.itextpdf.text.pdf.PdfWriter;
public void doGet(HttpServletRequest request, HttpServletResponse response)
    throws ServletException, IOException {


   Document doc = new Document();  
       ByteArrayOutputStream ba = new ByteArrayOutputStream();  
      try {  
           PdfWriter writer = PdfWriter.getInstance(doc, ba);  
           doc.open();  
           doc.add(new Paragraph("Hello World cc"));  

       } catch (DocumentException e) {  
           e.printStackTrace();  
       }  
       doc.close();  
       response.addHeader("Content-Disposition","attachment;filename=" + "test.pdf");
       response.setContentType("application/pdf");  
       response.setContentLength(ba.size());  
       ServletOutputStream out = response.getOutputStream();  
       ba.writeTo(out);  
       out.flush();