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- /*
- * Licensed to the Apache Software Foundation (ASF) under one or more
- * contributor license agreements. See the NOTICE file distributed with
- * this work for additional information regarding copyright ownership.
- * The ASF licenses this file to You under the Apache License, Version 2.0
- * (the "License"); you may not use this file except in compliance with
- * the License. You may obtain a copy of the License at
- *
- * http://www.apache.org/licenses/LICENSE-2.0
- *
- * Unless required by applicable law or agreed to in writing, software
- * distributed under the License is distributed on an "AS IS" BASIS,
- * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
- * See the License for the specific language governing permissions and
- * limitations under the License.
- */
-
- /* $Id$ */
-
- package org.apache.fop.pdf;
-
- import java.security.MessageDigest;
- import java.security.NoSuchAlgorithmException;
- import java.text.DateFormat;
- import java.text.SimpleDateFormat;
- import java.util.Date;
- import java.util.Random;
-
- /**
- * A class to generate the File Identifier of a PDF document (the ID entry of the file
- * trailer dictionary).
- */
- abstract class FileIDGenerator {
-
- abstract byte[] getOriginalFileID();
-
- abstract byte[] getUpdatedFileID();
-
- private static final class RandomFileIDGenerator extends FileIDGenerator {
-
- private byte[] fileID;
-
- private RandomFileIDGenerator() {
- Random random = new Random();
- fileID = new byte[16];
- random.nextBytes(fileID);
- }
-
- @Override
- byte[] getOriginalFileID() {
- return fileID;
- }
-
- @Override
- byte[] getUpdatedFileID() {
- return fileID;
- }
-
- }
-
- private static final class DigestFileIDGenerator extends FileIDGenerator {
-
- private byte[] fileID;
-
- private final PDFDocument document;
-
- private final MessageDigest digest;
-
- DigestFileIDGenerator(PDFDocument document) throws NoSuchAlgorithmException {
- this.document = document;
- this.digest = MessageDigest.getInstance("MD5");
- }
-
- @Override
- byte[] getOriginalFileID() {
- if (fileID == null) {
- generateFileID();
- }
- return fileID;
- }
-
- @Override
- byte[] getUpdatedFileID() {
- return getOriginalFileID();
- }
-
- private void generateFileID() {
- DateFormat df = new SimpleDateFormat("yyyy'-'MM'-'dd'T'HH':'mm':'ss'.'SSS");
- digest.update(PDFDocument.encode(df.format(new Date())));
- // Ignoring the filename here for simplicity even though it's recommended
- // by the PDF spec
- digest.update(PDFDocument.encode(String.valueOf(document.getCurrentFileSize())));
- digest.update(document.getInfo().toPDF());
- fileID = digest.digest();
- }
-
- }
-
- /**
- * Use this method when the file ID is needed before the document is finalized. The
- * digest method recommended by the PDF Reference is based, among other things, on the
- * file size.
- *
- * @return an instance that generates a random sequence of bytes for the File
- * Identifier
- */
- static FileIDGenerator getRandomFileIDGenerator() {
- return new RandomFileIDGenerator();
- }
-
- /**
- * Returns an instance that generates a file ID using the digest method recommended by
- * the PDF Reference. To properly follow the Reference, the size of the document must
- * no longer change after this method is called.
- *
- * @param document the document whose File Identifier must be generated
- * @return the generator
- * @throws NoSuchAlgorithmException if the MD5 Digest algorithm is not available
- */
- static FileIDGenerator getDigestFileIDGenerator(PDFDocument document)
- throws NoSuchAlgorithmException {
- return new DigestFileIDGenerator(document);
- }
- }
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