Serve merged PDF on servlet

PDFMerger.java

package testPackage;

import java.io.ByteArrayOutputStream;
import java.io.IOException;
import java.io.InputStream;
import java.util.ArrayList;
import java.util.Iterator;
import java.util.List;

import com.itextpdf.text.Document;
import com.itextpdf.text.pdf.PdfContentByte;
import com.itextpdf.text.pdf.PdfImportedPage;
import com.itextpdf.text.pdf.PdfReader;
import com.itextpdf.text.pdf.PdfWriter;

/** A PDF merger using iText */

public class PDFMerger {
 
    /**
     * @param streamOfPDFFiles
     * @param outputStream
     * @param paginate
     * @return a byte array of the merged PDF
     */
    public static byte[] concatPDFs(List<InputStream> pdfs, ByteArrayOutputStream outputStream) {
        Document document = new Document();
        
        try {
            List<PdfReader> readers = new ArrayList<PdfReader>();
            int totalPages = 0;
            Iterator<InputStream> iteratorPDFs = pdfs.iterator();
 
            // Create Readers for the pdfs.
            while (iteratorPDFs.hasNext()) {
                InputStream pdf = iteratorPDFs.next();
                PdfReader pdfReader = new PdfReader(pdf);
                readers.add(pdfReader);
                pdf.close();
                totalPages += pdfReader.getNumberOfPages();
            }
            
            // Create a writer for the outputstream
            PdfWriter writer = PdfWriter.getInstance(document, outputStream);
 
            document.open();
            
            PdfContentByte cb = writer.getDirectContent(); // Holds the PDF data
 
            PdfImportedPage page;
            int currentPageNumber = 0;
            int pageOfCurrentReaderPDF = 0;
            Iterator<PdfReader> iteratorPDFReader = readers.iterator();
 
            // Loop through the PDF files and add to the output.
            while (iteratorPDFReader.hasNext()) {
                PdfReader pdfReader = iteratorPDFReader.next();

                // Create a new page in the target for each source page.
                while (pageOfCurrentReaderPDF < pdfReader.getNumberOfPages()) {
                	// Set document size based on the original PDF's size
                	document.setPageSize(pdfReader.getCropBox(++pageOfCurrentReaderPDF));
                    document.newPage();              
                    currentPageNumber++;                 
                    page = writer.getImportedPage(pdfReader,
                            pageOfCurrentReaderPDF);
                    cb.addTemplate(page, 0, 0);          
                }
                pageOfCurrentReaderPDF = 0;
            }
            outputStream.flush();
            document.close();
            outputStream.close();
        } catch (Exception e) {
            e.printStackTrace();
        } finally {
            if (document.isOpen())
                document.close();
            try {
                if (outputStream != null)
                    outputStream.close();
            } catch (IOException ioe) {
                ioe.printStackTrace();
            }
        }
        return outputStream.toByteArray();
    }
}

TestServlet.java

package testPackage;

import java.io.*;
import java.util.ArrayList;
import java.util.List;

import javax.servlet.*;
import javax.servlet.annotation.*;
import javax.servlet.http.*;

import org.apache.tomcat.util.http.fileupload.IOUtils;

/** Simple servlet for displaying the merged PDF */

@WebServlet("/pdf")
public class TestServlet extends HttpServlet {

	private static byte[] PDF;
	
	static {
		mergePDF();
	}
	
	// Replace this method's content with your PDFs
	public static void mergePDF() {
		try {
			List<InputStream> pdfs = new ArrayList<InputStream>();
			pdfs.add(new FileInputStream("test.pdf"));
			pdfs.add(new FileInputStream("test2.pdf"));
			ByteArrayOutputStream output = new ByteArrayOutputStream();
			PDF = PDFMerger.concatPDFs(pdfs, output);
		} catch (Exception e) {
			e.printStackTrace();
		}
	}

	@Override
	public void doGet(HttpServletRequest request, HttpServletResponse response)
			throws ServletException, IOException {
		
		InputStream is = new ByteArrayInputStream(PDF);

		// Set response headers
		response.setHeader("Expires", "0");
		response.setHeader("Cache-Control", "must-revalidate, post-check=0, pre-check=0");
		response.setHeader("Pragma", "public");
		response.setContentType("application/pdf");
		response.setContentLength(PDF.length);

		OutputStream os = response.getOutputStream();
		IOUtils.copy(is, os);

		os.flush();
		os.close();

	}
}