使用 iText7 在高亮注释上设置外观流

Question

我有一个 PDF 查看器，如果没有外观流，它不会显示高亮显示。我正在 java 中试用 iText 7 核心，尝试向 PDF 添加高亮注释，但这些注释没有外观流，因此我希望在将注释写入 PDF 时尝试自己添加它们文件。

我遇到了旧答案，但它适用于 C# 和 iText 5，我似乎无法弄清楚如何在 iText 7 中复制它并取得成功。

所以我的问题是：如何在 iText 7 核心中的高亮注释上设置外观流？

我对代码的最深入了解如下所示。我正在使用 RegexBasedLocationExtrationStrategy class 查找 pdf 中所有搜索词的位置。

RegexBasedLocationExtractionStrategy evntlstnr = new RegexBasedLocationExtractionStrategy(pattern);
for (int pIdx = 0; pIdx < pdfDoc.getNumberOfPages(); ++pIdx) {
    final PdfPage page = pdfDoc.getPage(pIdx + 1);
    new PdfCanvasProcessor(evntlstnr).processPageContent(page);
    Collection<IPdfTextLocation> locations =  evntlstnr.getResultantLocations();
    for (IPdfTextLocation location : locations) {
        Rectangle rect = location.getRectangle();
        // Specify quad points in Z-like order
        // [0,1] x1,y1   [2,3] x2,y2
        // [4,5] x3,y3   [6,7] x4,y4
        float[] quads = new float[8];
        quads[0] = rect.getX();
        quads[1] = rect.getY() + rect.getHeight();
        quads[2] = rect.getX() + rect.getWidth();
        quads[3] = quads[1];
        quads[4] = quads[0];
        quads[5] = rect.getY();
        quads[6] = quads[2];
        quads[7] = quads[5];

        Color highlightColor = new DeviceRgb(0f, 0f, 1f);
        PdfTextMarkupAnnotation highlight = PdfTextMarkupAnnotation.createHighLight(rect, quads);
        highlight.setColor(highlightColor);


        Rectangle appearRect = new Rectangle(0f, 0f, rect.getWidth(), rect.getHeight());                            
        PdfFormXObject appearObj = new PdfFormXObject(appearRect);                                                        
        final PdfResources appearRes = appearObj.getResources();

        PdfExtGState extGState = new PdfExtGState();
        extGState.setBlendMode(PdfExtGState.BM_MULTIPLY);
        appearRes.addExtGState(extGState);
        appearObj.setBBox(new PdfArray(new float[] {0f, 0f, rect.getWidth(), rect.getHeight()}));

        PdfShading appearShading = new PdfShading.Axial(highlightColor.getColorSpace(), 0f, 0f, highlightColor.getColorValue(), 1f, 1f, highlightColor.getColorValue());                                                     
        appearRes.addShading(appearShading);

        appearRes.addColorSpace(highlightColor.getColorSpace());                            

        PdfAnnotationAppearance appearance = new PdfAnnotationAppearance(appearObj.getPdfObject());
        highlight.setNormalAppearance(appearance);
        highlight.setFlag(PdfAnnotation.PRINT);
        page.addAnnotation(highlight);
    }
}

Answer 1

使用 Samuel 的回答，我偶然发现了一个可行的答案。

我对 PDF 标准和这个框架 (iText) 没有期望，但我的假设是，根据我下面的工作示例，我试图为突出显示编写的矩形是一个粗略的回退当查看器无法呈现注释时 "faking" 突出显示矩形的方法（因为它们没有外观流）。意识到这两个操作没有关联，我来到了下面显示的工作示例。希望这对以后的其他人有帮助。

RegexBasedLocationExtractionStrategy evntlstnr = new RegexBasedLocationExtractionStrategy(pattern);
for (int pIdx = 0; pIdx < pdfDoc.getNumberOfPages(); ++pIdx) {
    final PdfPage page = pdfDoc.getPage(pIdx + 1);
    new PdfCanvasProcessor(evntlstnr).processPageContent(page);
    Collection<IPdfTextLocation> locations =  evntlstnr.getResultantLocations();
    for (IPdfTextLocation location : locations) {
        Rectangle rect = location.getRectangle();
        // Specify quad points in Z-like order
        // [0,1] x1,y1   [2,3] x2,y2
        // [4,5] x3,y3   [6,7] x4,y4
        float[] quads = new float[8];
        quads[0] = rect.getX();
        quads[1] = rect.getY() + rect.getHeight();
        quads[2] = rect.getX() + rect.getWidth();
        quads[3] = quads[1];
        quads[4] = quads[0];
        quads[5] = rect.getY();
        quads[6] = quads[2];
        quads[7] = quads[5];

        Color highlightColor = new DeviceRgb(1f, 1f, 0f);                                                                                                                           

        PdfTextMarkupAnnotation highlight = PdfTextMarkupAnnotation.createHighLight(rect, quads);
        highlight.setColor(highlightColor); 
        highlight.setFlag(PdfAnnotation.PRINT);
        page.addAnnotation(highlight);                            

        PdfCanvas canvas = new PdfCanvas(page);
        PdfExtGState extGState = new PdfExtGState();
        extGState.setBlendMode(PdfExtGState.BM_MULTIPLY);
        canvas.setExtGState(extGState);
        canvas.rectangle(rect.getX(), rect.getY(), rect.getWidth(), rect.getHeight());
        canvas.setFillColor(highlightColor);
        canvas.fill();                            
        canvas.release();                                                        
    }
}

使用 iText7 在高亮注释上设置外观流

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