在java中使用iText pdf替换pdf页面的颜色 [英] Change the color of pdf pages alternatively using iText pdf in java

问题描述

我正在根据客户活动创建报告。
我在iText PDF库的帮助下创建此报告。
我想用蓝色背景颜色创建前两页（产品名称和免责声明）
，其余页面为白色（没有背景颜色）。
我在报告的最开始使用以下代码为蓝色着色了两页。

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 );

但是当我使用 document.newpage（）移至第3页时，页面仍为蓝色。
我无法改变第3页的颜色。我想将第3页的颜色改为白色。
如何使用iText进行此操作？

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?

推荐答案

这是如何使用iText添加pdf的页面背景颜色在java

虽然在回答这个问题时给出的建议有效，但这不是你能得到的最佳建议。如果我之前看过你原来的问题，我会以不同的方式回答。我会建议您使用页面事件，就像在 PageBackgrounds 示例中所做的那样。

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.

在这个例子中，我为第1页和第2页创建了一个蓝色背景，为所有后续偶数页创建了一个灰色背景。请参阅 page_backgrounds.pdf

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

这是如何实现的？好吧，使用与我对这个相关问题的答案中使用的技术相同的技术：如何使用iText库5.5.2绘制整个pdf页面的边框

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

我创建了一个页面事件像这样：

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();
    }
}

如您所见，我首先检查页面数。如果它是一个奇数，如果它不等于1，我什么都不做。

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.

但是，如果我在第1页或第2页，或者如果页码是偶数，我从编写器获取内容，我从文档中获取页面的维度 。然后我将填充颜色设置为蓝色或浅灰色（取决于页码），然后构建覆盖整个页面的矩形的路径。最后，我用填充颜色填充该矩形。

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.

现在我们已经获得了自定义背景事件，我们可以像这样使用它：

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);

如果背景类，请随意调整你需要一个不同的行为。

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

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