一、PDF 页面坐标系

• PDF 页面的原点 (0, 0) 位于页面的左下角，X 轴向右为正，Y 轴向上为正

二、PDF 页面尺寸获取

PDPage page = new PDPage();

PDRectangle mediaBox = page.getMediaBox();

float width = mediaBox.getWidth();
float height = mediaBox.getHeight();

System.out.println("mediaBox: " + mediaBox);
System.out.println("width: " + width);
System.out.println("height: " + height);

# 输出结果

mediaBox: [0.0,0.0,612.0,792.0]
width: 612.0
height: 792.0

try (PDDocument document = PDDocument.load(new File("pdf/example.pdf"))) {
    PDPage page = document.getPage(0);

    PDRectangle mediaBox = page.getMediaBox();

    float width = mediaBox.getWidth();
    float height = mediaBox.getHeight();

    System.out.println("mediaBox: " + mediaBox);
    System.out.println("width: " + width);
    System.out.println("height: " + height);
} catch (Exception e) {
    e.printStackTrace();
}

# 输出结果

mediaBox: [0.0,0.0,612.0,792.0]
width: 612.0
height: 792.0

三、PDF 页面位置计算

1、使图片位于 PDF 页面的左上角

try (PDDocument document = new PDDocument()) {
    PDPage page = new PDPage();
    document.addPage(page);

    PDImageXObject pdImage = PDImageXObject.createFromFile("pdf/dzs.jpeg", document);

    try (PDPageContentStream contentStream = new PDPageContentStream(document, page)) {

        // 获取 PDF 页面的尺寸
        PDRectangle mediaBox = page.getMediaBox();
        float pdfWidth = mediaBox.getWidth();
        float pdfHeight = mediaBox.getHeight();

        // 获取图片的尺寸
        float imgWidth = pdImage.getWidth() * 0.25f;
        float imgHeight = pdImage.getHeight() * 0.25f;

        float x = 0;
        float y = pdfHeight - imgHeight;

        contentStream.drawImage(pdImage, x, y, imgWidth, imgHeight);
    } catch (IOException e) {
        e.printStackTrace();
    }

    document.save("pdf/image_position_example.pdf");
} catch (IOException e) {
    e.printStackTrace();
}

2、使图片位于 PDF 页面的左下角

...

float x = 0;
float y = 0;

...

3、使图片位于 PDF 页面的右上角

...

float x = pdfWidth - imgWidth;
float y = pdfHeight - imgHeight;

...

4、使图片位于 PDF 页面的右下角

...

float x = pdfWidth - imgWidth;
float y = 0;

...

5、使图片靠左垂直居中

...

float x = 0;
float y = (pdfHeight - imgHeight) / 2;

...

6、使图片靠右垂直居中

...

float x = pdfWidth - imgWidth;
float y = (pdfHeight - imgHeight) / 2;

...

7、使图片靠上水平居中

...

float x = (pdfWidth - imgWidth) / 2;
float y = pdfHeight - imgHeight;

...

8、使图片靠下水平居中

...

float x = (pdfWidth - imgWidth) / 2;
float y = 0;

...

9、使图片居中

...

float x = (pdfWidth - imgWidth) / 2;
float y = (pdfHeight - imgHeight) / 2;

...