Change the color of pdf pages alternatively using iText pdf in java

问题

I'm creating report based on client activity. I'm creating this report with the help of the iText PDF library. I want to create the first two pages with a blue background color (for product name and disclaimer notes) and the remaining pages in white (without a background color). I colored two pages at the very beginning of report with blue using following code.

Rectangle pageSize = new Rectangle(PageSize.A4);
pageSize.setBackgroundColor(new BaseColor(84, 141, 212));
Document document = new Document( pageSize );

But when I move to 3rd page using document.newpage(), the page is still in blue. I can't change the color of 3rd page. I want to change the color of 3rd page onward to white. How can I do this using iText?

回答1:

This is a follow-up question of How can I add page background color of pdf using iText in java

While the advice given in the answer to that question works, it's not the best advice you could get. If I had seen your original question earlier, I would have answered it differently. I would have recommended you to use page events, as is done in the PageBackgrounds example.

In this example, I create a blue background for page 1 and 2, and a grey background for all the subsequent even pages. See page_backgrounds.pdf

How is this achieved? Well, using the same technique as used in my answer to this related question: How to draw border for whole pdf pages using iText library 5.5.2

I create a page event like this:

public class Background extends PdfPageEventHelper {
    @Override
    public void onEndPage(PdfWriter writer, Document document) {
        int pagenumber = writer.getPageNumber();
        if (pagenumber % 2 == 1 && pagenumber != 1)
            return;
        PdfContentByte canvas = writer.getDirectContentUnder();
        Rectangle rect = document.getPageSize();
        canvas.setColorFill(pagenumber < 3 ? BaseColor.BLUE : BaseColor.LIGHT_GRAY);
        canvas.rectangle(rect.getLeft(), rect.getBottom(), rect.getWidth(), rect.getHeight());
        canvas.fill();
    }
}

As you can see, I first check for the page number. If it's an odd number and if it's not equal to 1, I don't do anything.

However, if I'm on page 1 or 2, or if the page number is even, I get the content from the writer, and I get the dimension of the page from the document. I then set the fill color to either blue or light gray (depending on the page number), and I construct the path for a rectangle that covers the complete page. Finally, I fill that rectangle with the fill color.

Now that we've got our custom Background event, we can use it like this:

PdfWriter writer = PdfWriter.getInstance(document, new FileOutputStream(filename));
Background event = new Background();
writer.setPageEvent(event);

Feel free to adapt the Background class if you need a different behavior.

来源：https://stackoverflow.com/questions/30211043/change-the-color-of-pdf-pages-alternatively-using-itext-pdf-in-java

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java

itextpdf