使用PDFBox和VB.NET检测粗体,斜体和打击文本

Dim doc As PDDocument = Nothing

    Try
        doc = PDDocument.load(RFPFilePath)
        Dim stripper As New PDFTextStripper()

        stripper.setAddMoreFormatting(True)
        stripper.setSortByPosition(True)
        rtxt_DocumentViewer.Text = stripper.getText(doc)

    Finally
        If doc IsNot Nothing Then
            doc.close()
        End If
    End Try

正如在一个Java示例所做的评论中提到的OP,我还只使用了JavaBox和Java,这个答案以Java示例为特色.此外,此示例仅使用PDFBox版本1.8.11进行开发和测试.

自定义文本剥离器

正如评论中已经提到的,

The bold and italic effects in the OP’s sample document are generated by using a different font (containing bold or italic versions of the letters) to draw the text. The underline and strike-through effects in the sample document are generated by drawing a rectangle under / through the text line which has the width of the text line and a very small height. To extract these information,therefore,one has to extend the PDFTextStripper to somehow react to font changes and rectangles nearby text.

这是一个扩展PDFTextStripper的示例类,如下所示：

public class PDFStyledTextStripper extends PDFTextStripper
{
    public PDFStyledTextStripper() throws IOException
    {
        super();
        registerOperatorProcessor("re",new AppendRectangleToPath());
    }

    @Override
    protected void writeString(String text,List<TextPosition> textPositions) throws IOException
    {
        for (TextPosition textPosition : textPositions)
        {
            Set<String> style = determineStyle(textPosition);
            if (!style.equals(currentStyle))
            {
                output.write(style.toString());
                currentStyle = style;
            }
            output.write(textPosition.getCharacter());
        }
    }

    Set<String> determineStyle(TextPosition textPosition)
    {
        Set<String> result = new HashSet<>();

        if (textPosition.getFont().getBaseFont().toLowerCase().contains("bold"))
            result.add("Bold");

        if (textPosition.getFont().getBaseFont().toLowerCase().contains("italic"))
            result.add("Italic");

        if (rectangles.stream().anyMatch(r -> r.underlines(textPosition)))
            result.add("Underline");

        if (rectangles.stream().anyMatch(r -> r.strikesThrough(textPosition)))
            result.add("StrikeThrough");

        return result;
    }

    class AppendRectangleToPath extends OperatorProcessor
    {
        public void process(PDFOperator operator,List<COSBase> arguments)
        {
            COSNumber x = (COSNumber) arguments.get(0);
            COSNumber y = (COSNumber) arguments.get(1);
            COSNumber w = (COSNumber) arguments.get(2);
            COSNumber h = (COSNumber) arguments.get(3);

            double x1 = x.doubleValue();
            double y1 = y.doubleValue();

            // create a pair of coordinates for the transformation
            double x2 = w.doubleValue() + x1;
            double y2 = h.doubleValue() + y1;

            Point2D p0 = transformedPoint(x1,y1);
            Point2D p1 = transformedPoint(x2,y1);
            Point2D p2 = transformedPoint(x2,y2);
            Point2D p3 = transformedPoint(x1,y2);

            rectangles.add(new TransformedRectangle(p0,p1,p2,p3));
        }

        Point2D.Double transformedPoint(double x,double y)
        {
            double[] position = {x,y}; 
            getGraphicsState().getCurrentTransformationMatrix().createAffineTransform().transform(
                    position,position,1);
            return new Point2D.Double(position[0],position[1]);
        }
    }

    static class TransformedRectangle
    {
        public TransformedRectangle(Point2D p0,Point2D p1,Point2D p2,Point2D p3)
        {
            this.p0 = p0;
            this.p1 = p1;
            this.p2 = p2;
            this.p3 = p3;
        }

        boolean strikesThrough(TextPosition textPosition)
        {
            Matrix matrix = textPosition.getTextPos();
            // TODO: This is a very simplistic implementation only working for horizontal text without page rotation
            // and horizontal rectangular strikeThroughs with p0 at the left bottom and p2 at the right top

            // Check if rectangle horizontally matches (at least) the text
            if (p0.getX() > matrix.getXPosition() || p2.getX() < matrix.getXPosition() + textPosition.getWidth() - textPosition.getFontSizeInPt() / 10.0)
                return false;
            // Check whether rectangle vertically is at the right height to underline
            double vertDiff = p0.getY() - matrix.getYPosition();
            if (vertDiff < 0 || vertDiff > textPosition.getFont().getFontDescriptor().getAscent() * textPosition.getFontSizeInPt() / 1000.0)
                return false;
            // Check whether rectangle is small enough to be a line
            return Math.abs(p2.getY() - p0.getY()) < 2;
        }

        boolean underlines(TextPosition textPosition)
        {
            Matrix matrix = textPosition.getTextPos();
            // TODO: This is a very simplistic implementation only working for horizontal text without page rotation
            // and horizontal rectangular underlines with p0 at the left bottom and p2 at the right top

            // Check if rectangle horizontally matches (at least) the text
            if (p0.getX() > matrix.getXPosition() || p2.getX() < matrix.getXPosition() + textPosition.getWidth() - textPosition.getFontSizeInPt() / 10.0)
                return false;
            // Check whether rectangle vertically is at the right height to underline
            double vertDiff = p0.getY() - matrix.getYPosition();
            if (vertDiff > 0 || vertDiff < textPosition.getFont().getFontDescriptor().getDescent() * textPosition.getFontSizeInPt() / 500.0)
                return false;
            // Check whether rectangle is small enough to be a line
            return Math.abs(p2.getY() - p0.getY()) < 2;
        }

        final Point2D p0,p3;
    }

    final List<TransformedRectangle> rectangles = new ArrayList<>();
    Set<String> currentStyle = Collections.singleton("Undefined");
}

(PDFStyledTextStripper.java)

除了PDFTextStripper所做的,这个类也是

>使用AppendRectangleToPath运算符处理器内部类的实例从内容(使用re指令定义)收集矩形,
>从determineStyle中的示例文档中检查样式变体的文本,以及
>每当样式更改时,将新样式添加到writeString中的结果中.

注意：这仅仅是一个概念证明！尤其是

> TransformedRectangle.underlines(TextPosition)和TransformedRectangle#strikesThrough(TextPosition)中的测试实现非常简单,仅适用于没有页面旋转的水平文本和水平矩形strikeThroughs和下划线,左下角为p0,右上角为p2 ;
>收集所有矩形,而不是检查它们是否真的充满了可见的颜色;
>“粗体”和“斜体”的测试仅仅检查使用过的字体的名称,这通常是不够的.

测试输出

像这样使用PDFStyledTextStripper

String extractStyled(PDDocument document) throws IOException
{
    PDFTextStripper stripper = new PDFStyledTextStripper();
    stripper.setSortByPosition(true);
    return stripper.getText(document);
}

(从ExtractText.java开始,从测试方法testExtractStyledFromExampleDocument调用)

一个得到结果

[]This is an example of plain text 

[Bold]This is an example of bold text 
[] 
[Underline]This is an example of underlined text[] 

[Italic]This is an example of italic text  
[] 
[StrikeThrough]This is an example of strike through text[]  

[Italic,Bold]This is an example of bold,italic text

对于OP的样本文档

PS同时,PDFStyledTextStripper的代码也略有改变,也适用于在github问题中共享的示例文档,特别是其内部类TransformedRectangle的代码,参见. here.