java - 复制时 PDFBox 中的新文档中的页面被裁剪

Question

我正在尝试将单个 PDF 拆分为多个。就像 10 页文档变成 10 个单页文档。

PDDocument source = PDDocument.load(input_file);
PDDocument output = new PDDocument();
PDPage page = source.getPages().get(0);
output.addPage(page);
output.save(file);
output.close();

这里的问题是，新文档的页面大小与原始文档不同。因此，新文档中的某些文本被裁剪或丢失。我正在使用 PDFBox 2.0，如何避免这种情况？

更新:谢谢@mkl。

Splitter 发挥了魔力。这是更新后的工作部分，

public static void extractAndCreateDocument(SplitMeta meta, PDDocument source)
      throws IOException {

    File file = new File(meta.getFilename());

    Splitter splitter = new Splitter();
    splitter.setStartPage(meta.getStart());
    splitter.setEndPage(meta.getEnd());
    splitter.setSplitAtPage(meta.getEnd());

    List<PDDocument> docs = splitter.split(source);
    if(docs.size() > 0){
      PDDocument output = docs.get(0);
      output.save(file);
      output.close();
    }
  }

public class SplitMeta {

  private String filename;
  private int start;
  private int end;

  public SplitMeta() {
  }
}

Answer 1

不幸的是，OP 没有提供示例文档来重现该问题。因此，我必须猜测。

我认为问题是基于未立即链接到页面对象而是从其父级继承的对象。

在这种情况下，使用 PDDocument.addPage 是错误的选择，因为此方法仅将给定的页面对象添加到目标文档页面树，而不考虑继承的内容。

相反，应该使用PDDocument.importPage，其记录为:

/**
 * This will import and copy the contents from another location. Currently the content stream is stored in a scratch
 * file. The scratch file is associated with the document. If you are adding a page to this document from another
 * document and want to copy the contents to this document's scratch file then use this method otherwise just use
 * the {@link #addPage} method.
 * 
 * Unlike {@link #addPage}, this method does a deep copy. If your page has annotations, and if
 * these link to pages not in the target document, then the target document might become huge.
 * What you need to do is to delete page references of such annotations. See
 * <a href="http://stackoverflow.com/a/35477351/535646">here</a> for how to do this.
 *
 * @param page The page to import.
 * @return The page that was imported.
 * 
 * @throws IOException If there is an error copying the page.
 */
public PDPage importPage(PDPage page) throws IOException

实际上，即使这种方法也可能不够，因为它没有考虑所有继承的属性，但是查看 Splitter 实用程序类，我们会得到一个印象:

PDPage imported = getDestinationDocument().importPage(page);
imported.setCropBox(page.getCropBox());
imported.setMediaBox(page.getMediaBox());
// only the resources of the page will be copied
imported.setResources(page.getResources());
imported.setRotation(page.getRotation());
// remove page links to avoid copying not needed resources 
processAnnotations(imported);

使用辅助方法

private void processAnnotations(PDPage imported) throws IOException
{
    List<PDAnnotation> annotations = imported.getAnnotations();
    for (PDAnnotation annotation : annotations)
    {
        if (annotation instanceof PDAnnotationLink)
        {
            PDAnnotationLink link = (PDAnnotationLink)annotation;   
            PDDestination destination = link.getDestination();
            if (destination == null && link.getAction() != null)
            {
                PDAction action = link.getAction();
                if (action instanceof PDActionGoTo)
                {
                    destination = ((PDActionGoTo)action).getDestination();
                }
            }
            if (destination instanceof PDPageDestination)
            {
                // TODO preserve links to pages within the splitted result  
                ((PDPageDestination) destination).setPage(null);
            }
        }
        // TODO preserve links to pages within the splitted result  
        annotation.setPage(null);
    }
}

当您尝试将单个 PDF 拆分为多个(例如将 10 页文档拆分为 10 个单页文档)时，您可能需要使用此 Splitter 实用程序类按原样。

测试

为了测试这些方法，我使用了 PDF Clown 示例输出 AnnotationSample.Standard.pdf 的输出。因为该库严重依赖于页面树值的继承。因此，我使用 PDDocument.addPage、PDDocument.importPage 或 Splitter 将其唯一页面的内容复制到新文档，如下所示:

PDDocument source = PDDocument.load(resource);
PDDocument output = new PDDocument();
PDPage page = source.getPages().get(0);
output.addPage(page);
output.save(new File(RESULT_FOLDER, "PageAddedFromAnnotationSample.Standard.pdf"));
output.close();

( CopyPages.java 测试 testWithAddPage)

PDDocument source = PDDocument.load(resource);
PDDocument output = new PDDocument();
PDPage page = source.getPages().get(0);
output.importPage(page);
output.save(new File(RESULT_FOLDER, "PageImportedFromAnnotationSample.Standard.pdf"));
output.close();

( CopyPages.java 测试 testWithImportPage)

PDDocument source = PDDocument.load(resource);
Splitter splitter = new Splitter();
List<PDDocument> results = splitter.split(source);
Assert.assertEquals("Expected exactly one result document from splitting a single page document.", 1, results.size());
PDDocument output = results.get(0);
output.save(new File(RESULT_FOLDER, "PageSplitFromAnnotationSample.Standard.pdf"));
output.close();

( CopyPages.java 测试 testWithSplitter)

只有最终测试忠实地复制了页面。