输入：包含嵌入字体的(例如14个)PDF / A-1b文件列表.

处理：与Apache PDFBOX进行简单合并.

结果：1个文件大小(太大)的PDF / A-1b文件. (它几乎是所有源文件大小的总和).

问题：有没有办法减少生成的PDF的文件大小？

想法：删除冗余的嵌入字体.但是怎么样？这是正确的方法吗？

不幸的是,以下代码没有完成这项工作,但突出了明显的问题.

try (PDDocument document = PDDocument.load(new File("E:/tmp/16189_ZU_20181121195111_5544_2008-12-31_Standardauswertung.pdf"))) {

List collectedFonts = new ArrayList<>();

PDPageTree pages = document.getDocumentCatalog().getPages();

int pageNr = 0;

for (PDPage page : pages) {

pageNr++;

Iterable 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");

}

代码产生如下输出：

Page 1

COSName{F23} - PDTrueTypeFont ArialMT-Bold, embedded: true

COSName{F27} - PDTrueTypeFont ArialMT-Regular, embedded: true

Page 2

COSName{F23} - PDTrueTypeFont ArialMT-Bold, embedded: true

COSName{F33} - PDTrueTypeFont ArialMT-BoldItalic, embedded: true

COSName{F25} - PDTrueTypeFont ArialMT-Italic, embedded: true

COSName{F27} - PDTrueTypeFont ArialMT-Regular, embedded: true

Page 3

COSName{F23} - PDTrueTypeFont ArialMT-Bold, embedded: true

COSName{F25} - PDTrueTypeFont ArialMT-Italic, embedded: true

COSName{F27} - PDTrueTypeFont ArialMT-Regular, embedded: true

Page 4

COSName{F23} - PDTrueTypeFont ArialMT-Bold, embedded: true

COSName{F25} - PDTrueTypeFont ArialMT-Italic, embedded: true

COSName{F27} - PDTrueTypeFont ArialMT-Regular, embedded: true

Page 5

COSName{F23} - PDTrueTypeFont ArialMT-Bold, embedded: true

COSName{F33} - PDTrueTypeFont ArialMT-BoldItalic, embedded: true

COSName{F27} - PDTrueTypeFont ArialMT-Regular, embedded: true

Page 6

COSName{F23} - PDTrueTypeFont ArialMT-Bold, embedded: true

COSName{F33} - PDTrueTypeFont ArialMT-BoldItalic, embedded: true

COSName{F27} - PDTrueTypeFont ArialMT-Regular, embedded: true

Page 7

COSName{F23} - PDTrueTypeFont ArialMT-Bold, embedded: true

COSName{F33} - PDTrueTypeFont ArialMT-BoldItalic, embedded: true

COSName{F27} - PDTrueTypeFont ArialMT-Regular, embedded: true

Page 8

COSName{F23} - PDTrueTypeFont ArialMT-Bold, embedded: true

COSName{F25} - PDTrueTypeFont ArialMT-Italic, embedded: true

COSName{F27} - PDTrueTypeFont ArialMT-Regular, embedded: true

Page 9

COSName{F23} - PDTrueTypeFont ArialMT-Bold, embedded: true

COSName{F33} - PDTrueTypeFont ArialMT-BoldItalic, embedded: true

COSName{F25} - PDTrueTypeFont ArialMT-Italic, embedded: true

COSName{F27} - PDTrueTypeFont ArialMT-Regular, embedded: true

Page 10

COSName{F23} - PDTrueTypeFont ArialMT-Bold, embedded: true

COSName{F33} - PDTrueTypeFont ArialMT-BoldItalic, embedded: true

COSName{F25} - PDTrueTypeFont ArialMT-Italic, embedded: true

COSName{F27} - PDTrueTypeFont ArialMT-Regular, embedded: true

Page 11

COSName{F23} - PDTrueTypeFont ArialMT-Bold, embedded: true

COSName{F33} - PDTrueTypeFont ArialMT-BoldItalic, embedded: true

COSName{F27} - PDTrueTypeFont ArialMT-Regular, embedded: true

Page 12

COSName{F23} - PDTrueTypeFont ArialMT-Bold, embedded: true

COSName{F25} - PDTrueTypeFont ArialMT-Italic, embedded: true

COSName{F27} - PDTrueTypeFont ArialMT-Regular, embedded: true

Page 13

COSName{F23} - PDTrueTypeFont ArialMT-Bold, embedded: true

COSName{F25} - PDTrueTypeFont ArialMT-Italic, embedded: true

COSName{F27} - PDTrueTypeFont ArialMT-Regular, embedded: true

Page 14

COSName{F23} - PDTrueTypeFont ArialMT-Bold, embedded: true

COSName{F25} - PDTrueTypeFont ArialMT-Italic, embedded: true

COSName{F27} - PDTrueTypeFont ArialMT-Regular, embedded: true

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解决方法:

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,使用已查看的字体文件项替换字典中的实际字体文件项,删除了引用并可以进行压缩.通过这种方式,我能够将30 MB的文件缩小到大约6 MB.

File file = new File("test.pdf");

PDDocument doc = PDDocument.load(file);

Map 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));

也许这不是最优雅的方式,但它可以工作并保持PDF / A-1b的兼容性.

标签：java,pdf,fonts,pdfbox,filesize

来源： https://codeday.me/bug/20191006/1858483.html