Add: Option to remove the digital signature when merging (#1424)

src/main/java/stirling/software/SPDF/controller/api/MergeController.java

@@ -10,11 +10,16 @@ import java.util.ArrayList;
 import java.util.Arrays;
 import java.util.Comparator;
 import java.util.List;
+import java.util.stream.Collectors;
 
 import org.apache.pdfbox.Loader;
 import org.apache.pdfbox.multipdf.PDFMergerUtility;
 import org.apache.pdfbox.pdmodel.PDDocument;
+import org.apache.pdfbox.pdmodel.PDDocumentCatalog;
 import org.apache.pdfbox.pdmodel.PDPage;
+import org.apache.pdfbox.pdmodel.interactive.form.PDAcroForm;
+import org.apache.pdfbox.pdmodel.interactive.form.PDField;
+import org.apache.pdfbox.pdmodel.interactive.form.PDSignatureField;
 import org.slf4j.Logger;
 import org.slf4j.LoggerFactory;
 import org.springframework.http.ResponseEntity;
@@ -38,6 +43,7 @@ public class MergeController {
 
     private static final Logger logger = LoggerFactory.getLogger(MergeController.class);
 
+    // Merges a list of PDDocument objects into a single PDDocument
     public PDDocument mergeDocuments(List<PDDocument> documents) throws IOException {
         PDDocument mergedDoc = new PDDocument();
         for (PDDocument doc : documents) {
@@ -48,6 +54,7 @@ public class MergeController {
         return mergedDoc;
     }
 
+    // Returns a comparator for sorting MultipartFile arrays based on the given sort type
     private Comparator<MultipartFile> getSortComparator(String sortType) {
         switch (sortType) {
             case "byFileName":
@@ -108,37 +115,78 @@ public class MergeController {
                     "This endpoint merges multiple PDF files into a single PDF file. The merged file will contain all pages from the input files in the order they were provided. Input:PDF Output:PDF Type:MISO")
     public ResponseEntity<byte[]> mergePdfs(@ModelAttribute MergePdfsRequest form)
             throws IOException {
-        List<File> filesToDelete = new ArrayList<File>();
+        List<File> filesToDelete = new ArrayList<>(); // List of temporary files to delete
+        ByteArrayOutputStream docOutputstream =
+                new ByteArrayOutputStream(); // Stream for the merged document
+        PDDocument mergedDocument = null;
+
+        boolean removeCertSign = form.isRemoveCertSign();
+
         try {
             MultipartFile[] files = form.getFileInput();
-            Arrays.sort(files, getSortComparator(form.getSortType()));
-
-            PDFMergerUtility mergedDoc = new PDFMergerUtility();
-            ByteArrayOutputStream docOutputstream = new ByteArrayOutputStream();
+            Arrays.sort(
+                    files,
+                    getSortComparator(
+                            form.getSortType())); // Sort files based on the given sort type
 
+            PDFMergerUtility mergerUtility = new PDFMergerUtility();
             for (MultipartFile multipartFile : files) {
-                File tempFile = GeneralUtils.convertMultipartFileToFile(multipartFile);
-                filesToDelete.add(tempFile);
-                mergedDoc.addSource(tempFile);
+                File tempFile =
+                        GeneralUtils.convertMultipartFileToFile(
+                                multipartFile); // Convert MultipartFile to File
+                filesToDelete.add(tempFile); // Add temp file to the list for later deletion
+                mergerUtility.addSource(tempFile); // Add source file to the merger utility
+            }
+            mergerUtility.setDestinationStream(
+                    docOutputstream); // Set the output stream for the merged document
+            mergerUtility.mergeDocuments(null); // Merge the documents
+
+            byte[] mergedPdfBytes = docOutputstream.toByteArray(); // Get merged document bytes
+
+            // Load the merged PDF document
+            mergedDocument = Loader.loadPDF(mergedPdfBytes);
+
+            // Remove signatures if removeCertSign is true
+            if (removeCertSign) {
+                PDDocumentCatalog catalog = mergedDocument.getDocumentCatalog();
+                PDAcroForm acroForm = catalog.getAcroForm();
+                if (acroForm != null) {
+                    List<PDField> fieldsToRemove =
+                            acroForm.getFields().stream()
+                                    .filter(field -> field instanceof PDSignatureField)
+                                    .collect(Collectors.toList());
+
+                    if (!fieldsToRemove.isEmpty()) {
+                        acroForm.flatten(
+                                fieldsToRemove,
+                                false); // Flatten the fields, effectively removing them
+                    }
+                }
             }
 
-            mergedDoc.setDestinationFileName(
-                    files[0].getOriginalFilename().replaceFirst("[.][^.]+$", "") + "_merged.pdf");
-            mergedDoc.setDestinationStream(docOutputstream);
-
-            mergedDoc.mergeDocuments(null);
+            // Save the modified document to a new ByteArrayOutputStream
+            ByteArrayOutputStream baos = new ByteArrayOutputStream();
+            mergedDocument.save(baos);
 
+            String mergedFileName =
+                    files[0].getOriginalFilename().replaceFirst("[.][^.]+$", "")
+                            + "_merged_unsigned.pdf";
             return WebResponseUtils.bytesToWebResponse(
-                    docOutputstream.toByteArray(), mergedDoc.getDestinationFileName());
+                    baos.toByteArray(), mergedFileName); // Return the modified PDF
+
         } catch (Exception ex) {
             logger.error("Error in merge pdf process", ex);
             throw ex;
         } finally {
             for (File file : filesToDelete) {
                 if (file != null) {
-                    Files.deleteIfExists(file.toPath());
+                    Files.deleteIfExists(file.toPath()); // Delete temporary files
                 }
             }
+            docOutputstream.close();
+            if (mergedDocument != null) {
+                mergedDocument.close(); // Close the merged document
+            }
         }
     }
 }

src/main/java/stirling/software/SPDF/model/api/general/MergePdfsRequest.java

@@ -21,4 +21,10 @@ public class MergePdfsRequest extends MultiplePDFFiles {
             },
             defaultValue = "orderProvided")
     private String sortType = "orderProvided";
+
+    @Schema(
+            description =
+                    "Flag indicating whether to remove certification signatures from the merged PDF. If true, all certification signatures will be removed from the final merged document.",
+            example = "true")
+    private boolean isRemoveCertSign;
 }