如何使用pdfbox或其他java库减小合并PDF/A-1b文件的大小
输入:带有嵌入式字体的(如14)PDF/A-1b文件列表。如何使用pdfbox或其他java库减小合并PDF/A-1b文件的大小,java,pdf,fonts,pdfbox,filesize,Java,Pdf,Fonts,Pdfbox,Filesize,输入:带有嵌入式字体的(如14)PDF/A-1b文件列表。 处理:与Apache PDFBOX进行简单合并。 结果:1个PDF/A-1b文件,文件大(太大)。(它几乎是所有源文件大小的总和) 问题:有没有办法减小生成的PDF的文件大小? Idea:删除多余的嵌入式字体。但是怎么做呢?这是正确的方法吗 不幸的是,下面的代码没有完成这项工作,而是突出了明显的问题 try (PDDocument document = PDDocument.load(new File("E:/tmp/16189_ZU_
处理:与Apache PDFBOX进行简单合并。
结果:1个PDF/A-1b文件,文件大(太大)。(它几乎是所有源文件大小的总和) 问题:有没有办法减小生成的PDF的文件大小?
Idea:删除多余的嵌入式字体。但是怎么做呢?这是正确的方法吗 不幸的是,下面的代码没有完成这项工作,而是突出了明显的问题
try (PDDocument document = PDDocument.load(new File("E:/tmp/16189_ZU_20181121195111_5544_2008-12-31_Standardauswertung.pdf"))) {
List<COSName> collectedFonts = new ArrayList<>();
PDPageTree pages = document.getDocumentCatalog().getPages();
int pageNr = 0;
for (PDPage page : pages) {
pageNr++;
Iterable<COSName> names = page.getResources().getFontNames();
System.out.println("Page " + pageNr);
for (COSName name : names) {
collectedFonts.add(name);
System.out.print("\t" + name + " - ");
PDFont font = page.getResources().getFont(name);
System.out.println(font + ", embedded: " + font.isEmbedded());
page.getCOSObject().removeItem(COSName.F);
page.getResources().getCOSObject().removeItem(name);
}
}
document.save("E:/tmp/output.pdf");
}
感谢您的帮助……此答案中的代码试图优化文档,如OP的示例文档,即包含完全相同对象副本的文档,在本例中是完全相同的、完全嵌入的字体。它不只是将几乎相同的对象(例如,相同字体的多个子集)合并为一个联合子集
在对问题的评论过程中,很明显OP的PDF中的重复字体确实是源字体文件的完全相同的副本。要合并此类重复对象,必须收集文档的复杂对象(数组、字典、流),相互比较,然后合并重复对象
对于大型文档,文档中所有复杂对象的实际成对比较可能会花费太多时间,因此下面的代码计算这些对象的散列,并仅比较具有相同散列的对象
要合并重复项,代码将选择其中一个重复项,并将对任何其他重复项的所有引用替换为对所选重复项的引用,从而从文档对象池中删除其他重复项。为了更有效地执行此操作,代码最初不仅收集所有复杂对象,还收集对每个对象的所有引用
优化代码
这是用来优化PDDocument
的方法:
public void optimize(PDDocument pdDocument) throws IOException {
Map<COSBase, Collection<Reference>> complexObjects = findComplexObjects(pdDocument);
for (int pass = 0; ; pass++) {
int merges = mergeDuplicates(complexObjects);
if (merges <= 0) {
System.out.printf("Pass %d - No merged objects\n\n", pass);
break;
}
System.out.printf("Pass %d - Merged objects: %d\n\n", pass, merges);
}
}
(帮助器接口参考
与实现数组参考
和字典参考
)
以下帮助器方法和类最终会识别和合并重复项:
int mergeDuplicates(Map<COSBase, Collection<Reference>> complexObjects) throws IOException {
List<HashOfCOSBase> hashes = new ArrayList<>(complexObjects.size());
for (COSBase object : complexObjects.keySet()) {
hashes.add(new HashOfCOSBase(object));
}
Collections.sort(hashes);
int removedDuplicates = 0;
if (!hashes.isEmpty()) {
int runStart = 0;
int runHash = hashes.get(0).hash;
for (int i = 1; i < hashes.size(); i++) {
int hash = hashes.get(i).hash;
if (hash != runHash) {
int runSize = i - runStart;
if (runSize != 1) {
System.out.printf("Equal hash %d for %d elements.\n", runHash, runSize);
removedDuplicates += mergeRun(complexObjects, hashes.subList(runStart, i));
}
runHash = hash;
runStart = i;
}
}
int runSize = hashes.size() - runStart;
if (runSize != 1) {
System.out.printf("Equal hash %d for %d elements.\n", runHash, runSize);
removedDuplicates += mergeRun(complexObjects, hashes.subList(runStart, hashes.size()));
}
}
return removedDuplicates;
}
int mergeRun(Map<COSBase, Collection<Reference>> complexObjects, List<HashOfCOSBase> run) {
int removedDuplicates = 0;
List<List<COSBase>> duplicateSets = new ArrayList<>();
for (HashOfCOSBase entry : run) {
COSBase element = entry.object;
for (List<COSBase> duplicateSet : duplicateSets) {
if (equals(element, duplicateSet.get(0))) {
duplicateSet.add(element);
element = null;
break;
}
}
if (element != null) {
List<COSBase> duplicateSet = new ArrayList<>();
duplicateSet.add(element);
duplicateSets.add(duplicateSet);
}
}
System.out.printf("Identified %d set(s) of identical objects in run.\n", duplicateSets.size());
for (List<COSBase> duplicateSet : duplicateSets) {
if (duplicateSet.size() > 1) {
COSBase surviver = duplicateSet.remove(0);
Collection<Reference> surviverReferences = complexObjects.get(surviver);
for (COSBase object : duplicateSet) {
Collection<Reference> references = complexObjects.get(object);
for (Reference reference : references) {
reference.setTo(surviver);
surviverReferences.add(reference);
}
complexObjects.remove(object);
removedDuplicates++;
}
surviver.setDirect(false);
}
}
return removedDuplicates;
}
boolean equals(COSBase a, COSBase b) {
if (a instanceof COSArray) {
if (b instanceof COSArray) {
COSArray aArray = (COSArray) a;
COSArray bArray = (COSArray) b;
if (aArray.size() == bArray.size()) {
for (int i=0; i < aArray.size(); i++) {
if (!resolve(aArray.get(i)).equals(resolve(bArray.get(i))))
return false;
}
return true;
}
}
} else if (a instanceof COSDictionary) {
if (b instanceof COSDictionary) {
COSDictionary aDict = (COSDictionary) a;
COSDictionary bDict = (COSDictionary) b;
Set<COSName> keys = aDict.keySet();
if (keys.equals(bDict.keySet())) {
for (COSName key : keys) {
if (!resolve(aDict.getItem(key)).equals(bDict.getItem(key)))
return false;
}
// In case of COSStreams we strictly speaking should
// also compare the stream contents here. But apparently
// their hashes coincide well enough for the original
// hashing equality, so let's just assume...
return true;
}
}
}
return false;
}
static COSBase resolve(COSBase object) {
while (object instanceof COSObject)
object = ((COSObject)object).getObject();
return object;
}
(帮助器类hashofcbase
)
将代码应用于OP的示例文档
OP的示例文档大小约为6.5MB。像这样应用上面的代码
PDDocument pdDocument = PDDocument.load(SOURCE);
optimize(pdDocument);
pdDocument.save(RESULT);
结果生成的PDF大小小于700 KB,并且看起来是完整的
(如果丢失了什么,请告诉我,我会设法修复的。)
警告语
一方面,此优化器不会识别所有相同的重复项。特别是在循环引用的情况下,不会识别对象的重复圆,因为代码仅在重复对象圆的内容相同时才识别重复对象,而重复对象圆中通常不会出现这种情况
另一方面,在某些情况下,此优化器可能已经过于急切,因为PDF查看器可能需要一些重复项作为单独的对象来接受每个实例作为单独的实体
此外,该程序还涉及文件中的各种对象,甚至是定义PDF内部结构的对象,但它不会尝试更新管理此结构的任何PDFBox类(
PDDocument
,PDDocumentCatalog
,PDAcroForm
,…)。为了不让任何挂起的更改破坏整个文档,因此,请仅将此程序应用于新加载的、未修改的PDDocument
实例,然后立即保存,无需进一步的ado。在文件中调试时,我发现相同字体的字体文件被多次引用。因此,将字典中的实际字体文件项替换为已查看的字体文件项,即可删除引用并进行压缩。这样,我就可以将一个30MB的文件压缩到6MB左右
File file = new File("test.pdf");
PDDocument doc = PDDocument.load(file);
Map<String, COSBase> fontFileCache = new HashMap<>();
for (int pageNumber = 0; pageNumber < doc.getNumberOfPages(); pageNumber++) {
final PDPage page = doc.getPage(pageNumber);
COSDictionary pageDictionary = (COSDictionary) page.getResources().getCOSObject().getDictionaryObject(COSName.FONT);
for (COSName currentFont : pageDictionary.keySet()) {
COSDictionary fontDictionary = (COSDictionary) pageDictionary.getDictionaryObject(currentFont);
for (COSName actualFont : fontDictionary.keySet()) {
COSBase actualFontDictionaryObject = fontDictionary.getDictionaryObject(actualFont);
if (actualFontDictionaryObject instanceof COSDictionary) {
COSDictionary fontFile = (COSDictionary) actualFontDictionaryObject;
if (fontFile.getItem(COSName.FONT_NAME) instanceof COSName) {
COSName fontName = (COSName) fontFile.getItem(COSName.FONT_NAME);
fontFileCache.computeIfAbsent(fontName.getName(), key -> fontFile.getItem(COSName.FONT_FILE2));
fontFile.setItem(COSName.FONT_FILE2, fontFileCache.get(fontName.getName()));
}
}
}
}
}
final ByteArrayOutputStream baos = new ByteArrayOutputStream();
doc.save(baos);
final File compressed = new File("test_compressed.pdf");
baos.writeTo(new FileOutputStream(compressed));
File File=新文件(“test.pdf”);
PDDocument doc=PDDocument.load(文件);
Map fontFileCache=新建HashMap();
对于(int pageNumber=0;pageNumberfontFile.getItem(COSName.FONT_FILE2));
setItem(COSName.FONT_FILE2,fontFileCache.get(fontName.getName());
}
}
}
}
}
最终ByteArrayOutputStream bas=新ByteArrayOutputStream();
单据保存(baos);
最终文件压缩=新文件(“test_compressed.pdf”);
writeTo(新文件输出流(压缩));
也许这不是最优雅的方法,但它可以工作并保持PDF/A-1b的兼容性。我发现的另一种方法是以这种方式使用ITEXT 7(pdfWriter.setSmartMode):
字体是否完全嵌入?或者作为子集?@mkl从输出来看,它们似乎完全嵌入。因此,如果文件都来自同一个源,并且具有相同的字典,那么就可以真正替换字体资源中的对象
static class HashOfCOSBase implements Comparable<HashOfCOSBase> {
public HashOfCOSBase(COSBase object) throws IOException {
this.object = object;
this.hash = calculateHash(object);
}
int calculateHash(COSBase object) throws IOException {
if (object instanceof COSArray) {
int result = 1;
for (COSBase member : (COSArray)object)
result = 31 * result + member.hashCode();
return result;
} else if (object instanceof COSDictionary) {
int result = 3;
for (Map.Entry<COSName, COSBase> entry : ((COSDictionary)object).entrySet())
result += entry.hashCode();
if (object instanceof COSStream) {
try ( InputStream data = ((COSStream)object).createRawInputStream() ) {
MessageDigest md = MessageDigest.getInstance("MD5");
byte[] buffer = new byte[8192];
int bytesRead = 0;
while((bytesRead = data.read(buffer)) >= 0)
md.update(buffer, 0, bytesRead);
result = 31 * result + Arrays.hashCode(md.digest());
} catch (NoSuchAlgorithmException e) {
throw new IOException(e);
}
}
return result;
} else {
throw new IllegalArgumentException(String.format("Unknown complex COSBase type %s", object.getClass().getName()));
}
}
final COSBase object;
final int hash;
@Override
public int compareTo(HashOfCOSBase o) {
int result = Integer.compare(hash, o.hash);
if (result == 0)
result = Integer.compare(hashCode(), o.hashCode());
return result;
}
}
PDDocument pdDocument = PDDocument.load(SOURCE);
optimize(pdDocument);
pdDocument.save(RESULT);
File file = new File("test.pdf");
PDDocument doc = PDDocument.load(file);
Map<String, COSBase> fontFileCache = new HashMap<>();
for (int pageNumber = 0; pageNumber < doc.getNumberOfPages(); pageNumber++) {
final PDPage page = doc.getPage(pageNumber);
COSDictionary pageDictionary = (COSDictionary) page.getResources().getCOSObject().getDictionaryObject(COSName.FONT);
for (COSName currentFont : pageDictionary.keySet()) {
COSDictionary fontDictionary = (COSDictionary) pageDictionary.getDictionaryObject(currentFont);
for (COSName actualFont : fontDictionary.keySet()) {
COSBase actualFontDictionaryObject = fontDictionary.getDictionaryObject(actualFont);
if (actualFontDictionaryObject instanceof COSDictionary) {
COSDictionary fontFile = (COSDictionary) actualFontDictionaryObject;
if (fontFile.getItem(COSName.FONT_NAME) instanceof COSName) {
COSName fontName = (COSName) fontFile.getItem(COSName.FONT_NAME);
fontFileCache.computeIfAbsent(fontName.getName(), key -> fontFile.getItem(COSName.FONT_FILE2));
fontFile.setItem(COSName.FONT_FILE2, fontFileCache.get(fontName.getName()));
}
}
}
}
}
final ByteArrayOutputStream baos = new ByteArrayOutputStream();
doc.save(baos);
final File compressed = new File("test_compressed.pdf");
baos.writeTo(new FileOutputStream(compressed));
try (PdfWriter pdfWriter = new PdfWriter(out)) {
pdfWriter.setSmartMode(true); // Here happens the optimation, e.g. reducing redundantly embedded fonts
pdfWriter.setCompressionLevel(Deflater.BEST_COMPRESSION);
try (PdfDocument pdfDoc = new PdfADocument(pdfWriter, PdfAConformanceLevel.PDF_A_1B,
new PdfOutputIntent("Custom", "", "http://www.color.org", "sRGB IEC61966-2.1", colorProfile))) {
PdfMerger merger = new PdfMerger(pdfDoc);
merger.setCloseSourceDocuments(true);
try {
for (InputStream pdf : pdfs) {
try (PdfDocument doc = new PdfDocument(new PdfReader(pdf))) {
merger.merge(doc, createPageList(doc.getNumberOfPages()));
}
}
merger.close();
}
catch (com.itextpdf.kernel.crypto.BadPasswordException e) {
throw new BieneException("Konkatenierung eines passwortgeschützten PDF-Dokumentes nicht möglich: " + e.getMessage(),
e);
}
catch (com.itextpdf.io.IOException | PdfException e) {
throw new BieneException(e.getMessage(), e);
}
}
}