獲取所需合併的 PDF 檔案路徑即可。

/**
     * 合成 PDF
     * @param beforeRootPath: 專案路徑
     * @param filePath: 第一個 PDF 路徑
     * @param checkReport: 物件, 用於獲取使用者上傳的 PDF 路徑(欄位)
     * @return
     * @throws Exception
     */
    public String getPathSynthesisPdf(String beforeRootPath, String filePath, CheckReport checkReport) throws
 
 Exception{
        //合成後的檔案路徑("D:\\pdf\\aaaa.pdf")
        String synthesisPdfPath = "";
        SimpleDateFormat formatter = new SimpleDateFormat("yyyyMMddHHmmss");  
        synthesisPdfPath = beforeRootPath + "WEB-INF\\upload\\checkReport\\syntheticsPdf\\syntheticsPdf_" + formatter.format(new Date()) + "_鋁及鋁合金化學成分.pdf"
 
;
        PDFMergerUtility PDFmerger = new PDFMergerUtility();       
        PDFmerger.setDestinationFileName(synthesisPdfPath); 
        File file1 = new File(filePath); 
        File file2 = new File(checkReport.getSyPath() == null || checkReport.getSyPath().trim().length() == 0 ? "" : beforeRootPath + "WEB-INF\\upload\\checkReport\\uploadThreePDF\\"
 
 + checkReport.getSyPath()); 
        File file3 = new File(checkReport.getBgPath() == null || checkReport.getBgPath().trim().length() == 0 ? "" : beforeRootPath + "WEB-INF\\upload\\checkReport\\uploadThreePDF\\" + checkReport.getBgPath()); 
        File file4 = new File(checkReport.getYsPath() == null || checkReport.getYsPath().trim().length() == 0 ? "" : beforeRootPath + "WEB-INF\\upload\\checkReport\\uploadThreePDF\\" + checkReport.getYsPath()); 
        PDDocument doc1 = null; 
        PDDocument doc2 = null; 
        PDDocument doc3 = null; 
        PDDocument doc4 = null; 
        if(equalsStr(file2.getPath()) && equalsStr(file3.getPath()) && equalsStr(file4.getPath())){
            if(file1.getPath() != null && file1.getPath().trim().length() > 0){
                doc1 = PDDocument.load(file1);
                PDFmerger.addSource(file1); 
            }
            if(file2.getPath() != null && file2.getPath().trim().length() > 0){
                doc2 = PDDocument.load(file2);
                PDFmerger.addSource(file2); 
            }
            if(file3.getPath() != null && file3.getPath().trim().length() > 0){
                doc3  = PDDocument.load(file3);
                PDFmerger.addSource(file3); 
            }
            if(file4.getPath() != null && file4.getPath().trim().length() > 0){
                doc4  = PDDocument.load(file4);
                PDFmerger.addSource(file4); 
            }
            PDFmerger.mergeDocuments(); 
            if(doc1 != null){
                doc1.close(); 
            }
            if(doc2 != null){
                doc2.close(); 
            }
            if(doc3 != null){
                doc3.close(); 
            }
            if(doc4 != null){
                doc4.close(); 
            }
            System.out.println("使用者上傳的三個PDF和模板合成完成!"); 
        }else {
            throw new Exception("請先上傳附件!");
        }
        return synthesisPdfPath;
    }