Apache PDFBox Remove Spaces between characters

问题

We are using PDFBox to extract text from PDF's.

Some PDF's text can't be extract correctly. The following image shows a part from the PDF as image:

After text extraction we get the following text:
3, 8 5 EU R 1 Netto 38,50 EUR 4,00
(Spaces are added between ',' and '8')

Here is our code:

            PDDocument pdf = PDDocument.load(reuseableInputStream);
            PDFTextStripper pdfStripper = new PDFTextStripper();
            pdfStripper.setSortByPosition(true);
            String text = pdfStripper.getText(pdf);

We tried to play with the PDFTextStripper attributes 'AverageCharTolerance' and 'SpacingTolerance' with no positive effect.

The alternative libary 'iText' extract the text correctly without spaces between the characters. But we can't use it because of license problems.

Any ideas? Thank you.

EDIT: We are using version 1.8.9. We tried also the snapshot version 2.0.0 with no effect.

回答1:

The cause

Inspecting the file provided by the OP it turns out that the issue is caused by extra spaces actually being there! There are multiple strings drawn from the same starting position; at every position at most one of those strings has a non-space character. Thus, the PDF viewer output looks good, but PDFBox as text extractor tries to make use of all characters found including those extra space characters.

The behavior can be reproduced using a PDF with this content stream with F0 being Courier:

BT
/F0 9 Tf
100 500 Td
(             2                                                                  Netto        5,00 EUR 3,00) Tj
0 0 Td
(                2882892  ENERGIZE LR6 Industrial                     2,50 EUR 1) Tj
ET

In a PDF viewer this looks like this:

Copy & paste from Adobe Reader results in

2 2 8 8 2 8 9 2 E N E R G I Z E L R 6 I n d u s t r i a l 2 , 5 0 E U R 1 Netto 5,00 EUR 3,00

Regular extraction using PDFBox results in

             2    2 8 8 2 89 2    E N E RG  IZ  E  L R 6  I n du s t  ri  a l                      2 ,5  0  EU  R  1 Netto        5,00 EUR 3,00

Thus, not only PDFBox has problems here, these two outputs look different but the extra spaces are a problem either way.

I would propose telling the producer of those PDFs that they are difficult to post-process, even for widely-used software like Adobe Reader.

A work-around

To extract something sensible from this we have to somehow ignore the (actually existing!) extra spaces. As there is no way to ad hoc know which spaces can be used later on and which not, we simply remove all and hope PDFBox adds spaces where necessary:

String extractNoSpaces(PDDocument document) throws IOException
{
    PDFTextStripper stripper = new PDFTextStripper()
    {
        @Override
        protected void processTextPosition(TextPosition text)
        {
            String character = text.getCharacter();
            if (character != null && character.trim().length() != 0)
                super.processTextPosition(text);
        }
    };
    stripper.setSortByPosition(true);
    return stripper.getText(document);
}

(ExtractWithoutExtraSpaces.java)

Using this method with the test document we get:

2 2882892 ENERGIZE LR6 Industrial 2,50 EUR 1 Netto 5,00 EUR 3,00

Different text extractors

The alternative libary 'iText' extract the text correctly without spaces between the characters

This is due to iText extracting text string by string, not character by character. This procedure has its own perils but in this case results in something more usable out-of-the-box.

来源：https://stackoverflow.com/questions/29554400/apache-pdfbox-remove-spaces-between-characters

标签

pdfbox

text-extraction

pdf-parsing