concatenate pdfs (using iText)

PdfJoiner.java

import java.io.FileOutputStream;
import java.io.IOException;

import com.itextpdf.text.Document;
import com.itextpdf.text.DocumentException;
import com.itextpdf.text.pdf.PdfCopy;
import com.itextpdf.text.pdf.PdfImportedPage;
import com.itextpdf.text.pdf.PdfReader;
import com.itextpdf.text.pdf.RandomAccessFileOrArray;


public class PdfJoiner {

    public void join(String outputPath, String... inputPaths) {
        Document document = null;
        PdfCopy copy = null;

        try {
            for (String inputPath : inputPaths) {
                PdfReader reader = new PdfReader(new RandomAccessFileOrArray(inputPath), null); // ここがポイント
                reader.consolidateNamedDestinations();

                if (document == null) {
                    document = new Document(reader.getPageSizeWithRotation(1));
                    copy = new PdfCopy(document, new FileOutputStream(outputPath));
                    document.open();
                }

                PdfImportedPage page;
                int numberOfPages = reader.getNumberOfPages();
                for (int i = 1; i <= numberOfPages; i++) {
                    page = copy.getImportedPage(reader, i);
                    copy.addPage(page);
                }
                reader.close();
            }
            copy.close();
            document.close();

        } catch (IOException e) {
            throw new RuntimeException(e);

        } catch (DocumentException e) {
            throw new RuntimeException(e);

        } finally {
            if (document != null) {
                document.close();
            }
            if (copy != null) {
                copy.close();
            }
        }
    }
}