Java iText 将文档缩放到 A4

Question

我有以下方法可以将文档的所有页面“调整”为 A4 页面尺寸：

  for (PdfDocument doc : pdfDocuments) {
        int n = doc.getNumberOfPages();
     
        for (int i = 1; i <= n; i++) {
         
            PdfPage page = doc.getPage(i);
        
            Rectangle media = page.getCropBox();
            if (media == null) {
                media = page.getMediaBox();
            }
          
            Rectangle crop = new Rectangle(0, 0, 210, 297);
            page.setMediaBox(crop);
            page.setCropBox(crop);

            // The content, placed on a content stream before, will be rendered before the other content
            // and, therefore, could be understood as a background (bottom "layer")
            new PdfCanvas(page.newContentStreamBefore(),
                    page.getResources(), doc).writeLiteral("\nq 0.5 0 0 0.5 0 0 cm\nq\n");

            // The content, placed on a content stream after, will be rendered after the other content
            // and, therefore, could be understood as a foreground (top "layer")
            new PdfCanvas(page.newContentStreamAfter(),
                    page.getResources(), doc).writeLiteral("\nQ\nQ\n");
        }
    }

但是，这没有按预期工作，页面正在转换为 A4 (297x210)，但内容没有适合内部（缩放），内容显示为被剪切，因为原始页面大于 297X210。我该如何解决这个问题？

Answer 1

在您澄清的评论中

I want the bounding box of the former content be scaled and a margin be added in the target

所以，我们首先要确定原始页面内容的边界框。这可以使用MarginFinder class from 来完成。当心：class 确定所有内容的边界框，即使它只是一个白色矩形，在视觉上与没有内容或以前位于裁剪框之外的内容没有区别......如果您的用例需要它，您可能必须扩展 class 以将此类情况也考虑在内。

内容边界框确定后，剩下要做的就是一些计算。

以下方法使用上面的 class 确定边界框，相应地转换内容，并更改结果裁剪框。

void scale(PdfDocument pdfDocument, Rectangle pageSize, Rectangle pageBodySize) {
    int n = pdfDocument.getNumberOfPages();

    for (int i = 1; i <= n; i++) {
        PdfPage page = pdfDocument.getPage(i);

        MarginFinder marginFinder = new MarginFinder();
        PdfCanvasProcessor pdfCanvasProcessor = new PdfCanvasProcessor(marginFinder);
        pdfCanvasProcessor.processPageContent(page);
        Rectangle boundingBox = marginFinder.getBoundingBox();
        if (boundingBox == null || boundingBox.getWidth() == 0 || boundingBox.getHeight() == 0) {
            System.err.printf("Cannot scale page %d contents with bounding box %s\n", i , boundingBox);
            continue;
        } else {
            // Scale and move content into A4 with margin
            double scale = 0, xDiff= 0, yDiff = 0;
            double xScale = pageBodySize.getWidth()/boundingBox.getWidth();
            double yScale = pageBodySize.getHeight()/boundingBox.getHeight();
            if (xScale < yScale) {
                yDiff = boundingBox.getHeight() * (yScale / xScale - 1) / 2;
                scale = xScale;
            } else {
                xDiff = boundingBox.getWidth() * (xScale / yScale - 1) / 2;
                scale = yScale;
            }

            AffineTransform transform = AffineTransform.getTranslateInstance(pageBodySize.getLeft() + xDiff, pageBodySize.getBottom() + yDiff);
            transform.scale(scale, scale);
            transform.translate(-boundingBox.getLeft(), -boundingBox.getBottom());
            new PdfCanvas(page.newContentStreamBefore(), page.getResources(), pdfDocument)
                    .concatMatrix(transform);
        }
        page.setMediaBox(pageSize);
        page.setCropBox(pageSize);
    }
}

(ScaleToA4方法scale)

对于每边有一英寸边距的 A4 结果页面大小，您可以这样称呼 PdfDocument pdfDocument:

Rectangle pageSize = PageSize.A4;
Rectangle pageBodySize = pageSize.clone().applyMargins(72, 72, 72, 72, false);
scale(pdfDocument, pageSize, pageBodySize);

（摘自ScaleToA4测试testFdaRequiresUseOfEctdFormatAndStandardizedStudyDataInFutureRegulatorySubmissionsSept）

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