我有一个解析PDF文档的程序以获取信息.当发布新版本的PDF时,作者使用粗体或斜体文本来指示新信息,并使用Strike through或underlined来指示省略的文本.使用PDFBox中的基础剥离器类会返回所有文本,但格式化将被删除,因此我无法确定文本是新的还是省略.我目前正在使用下面的项目示例代码：
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
如果我只是将PDF文本复制并粘贴到保存格式的richtextBox中,我的解析代码就可以正常工作.我打算通过打开PDF,选择全部,复制,关闭文档然后将其粘贴到我的richtextBox中以编程方式执行此操作,但这看起来很笨拙.
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
PDFTextStripperto 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");
}
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.