maven坐标：

<dependency>
			<groupId>commons-io</groupId>
			<artifactId>commons-io</artifactId>
			<version>2.5</version>
		</dependency>
		<dependency>
			<groupId>com.lowagie</groupId>
			<artifactId>itext</artifactId>
			<version>2.1.7</version>
		</dependency>
		<dependency>
			<groupId>com.itextpdf</groupId>
			<artifactId>itextpdf</artifactId>
			<version>5.5.9</version>
		</dependency>
		<dependency>
			<groupId>com.itextpdf</groupId>
			<artifactId>itext-asian</artifactId>
			<version>5.2.0</version>
		</dependency>

 

实现：

public static byte[] mergePdfFiles(List<byte[]> files) throws IOException {
        Document document = new Document(PageSize.A4);
        ByteArrayOutputStream bos = new ByteArrayOutputStream();
        try {
            PdfCopy copy = new PdfCopy(document, bos);
            document.open();

            for (int i = 0; i < files.size(); i++) {
                byte[] bytesArray = files.get(i);
                PdfReader reader = new PdfReader(bytesArray);
                int n = reader.getNumberOfPages();
                for (int j = 1; j <= n; j++) {
                    document.newPage();
                    PdfImportedPage page = copy.getImportedPage(reader, j);
                    copy.addPage(page);
                }
            }



        } catch (Exception e) {
            e.printStackTrace();
        } finally {
            bos.flush();
            bos.close();
            document.close();
        }

        return bos.toByteArray();
    }