在没有重叠页面的itext 7中的行之间添加画布

Question

是否可以将canvas和addParagraph一起添加到文档中？我有很长的文字（1000页）。

我需要在某些地方（图形，形状等）的文本之间添加画布。

例如，如果文本中有单词“graph_add”

PdfDocument pdfDoc = new PdfDocument(new PdfWriter(DEST));
PageSize ps = PageSize.A4;;
Document doc = new Document(pdfDoc, ps);
BufferedReader br = new BufferedReader(new FileReader("bigfileWithText.txt"));
while ((line = br.readLine()) != null) {
if("graph_add".equals(line))
//Add canvas in document in this place!!doc.add(Canvas)
doc.add(new Paragraph(line)
}
doc.close();

这是示例文件：

这篇文章https://itextpdf.com/ru/resources/books/itext-7-building-blocks/chapter-2-adding-content-canvas-or-document不适合，这里我需要在一个单独的页面上创建。我在文本后的某个时刻添加了一个图形（Canvas），然后再添加一个文本。像这样的东西：

Answer 1

What to Add

首先，你不能简单地添加一个Canvas，因为Canvas只是帮助将内容直接添加到指定的PdfCanvas上，这是不同API级别之间的桥梁，参见它的JavaDoc：

/**
 * This class is used for adding content directly onto a specified {@link PdfCanvas}.
 * {@link Canvas} does not know the concept of a page, so it can't reflow to a 'next' {@link Canvas}.
 *
 * This class effectively acts as a bridge between the high-level <em>layout</em>
 * API and the low-level <em>kernel</em> API.
 */
public class Canvas extends RootElement<Canvas>

出于类似的原因，您无法添加PdfCanvas，因为它也只是帮助将内容直接添加到页面的内容流或表单XObject中：

/**
 * PdfCanvas class represents an algorithm for writing data into content stream.
 * To write into page content, create PdfCanvas from a page instance.
 * To write into form XObject, create PdfCanvas from a form XObject instance.
 * Make sure to call PdfCanvas.release() after you finished writing to the canvas.
 * It will save some memory.
 */
public class PdfCanvas implements Serializable

但是，你可以添加到某个东西，是将它包装到Image之后的XObject形式。

因此，您应首先创建一个表单XObject，然后是PdfCanvas，然后是Canvas，并用您的内容填充Canvas：

PdfFormXObject pdfFormXObject = new PdfFormXObject(XOBJECT_SIZE);
PdfCanvas pdfCanvas = new PdfCanvas(pdfFormXObject, pdfDoc);
try (Canvas canvas = new Canvas(pdfCanvas, pdfDoc, pdfFormXObject.getBBox().toRectangle())) {
    ADD CONTENT TO canvas AS REQUIRED FOR THE USE CASE IN QUESTION
}

然后，您可以将表单XObject包装在Image中并将其添加到文档中：

doc.add(new Image(pdfFormXObject));

An Example

我使用了您的示例文本和图形图像（存储为“Graph.png”）：

String text = "Until recently, increasing dividend yields grabbed the headlines. However, increasing\n" + 
        "yields were actually more a reflection of the market capitalisation challenge than of the\n" + 
        "fortunes of mining shareholders. The yields mask a complete u-turn from boom-time\n" + 
        "dividend policies. More companies have now announced clear percentages of profit\n" + 
        "distribution policies. The big story today is the abandonment of progressive dividends\n" + 
        "by the majors, confirming that no miner was immune from a sustained commodity\n" + 
        "cycle downturn, however diversified their portfolio. \n" +
        "\ngraph_add\n\n" +
        "Shareholders were not fully rewarded for the high commodity prices and huge\n" + 
        "profits experienced in the boom, as management ploughed cash and profits into\n" + 
        "bigger and more marginal assets. During those times, production was the main\n" + 
        "game and shareholders were rewarded through soaring stock prices. However,\n" + 
        "this investment proposition relied on prices remaining high. ";

final Image img;
try (InputStream imageResource = getClass().getResourceAsStream("Graph.png")) {
    ImageData data = ImageDataFactory.create(StreamUtil.inputStreamToArray(imageResource));
    img = new Image(data);
}

PdfDocument pdfDoc = new PdfDocument(new PdfWriter(DEST));
PageSize ps = PageSize.A4;;
Document doc = new Document(pdfDoc, ps);

Rectangle effectivePageSize = doc.getPageEffectiveArea(ps);
img.scaleToFit(effectivePageSize.getWidth(), effectivePageSize.getHeight());
PdfFormXObject pdfFormXObject = new PdfFormXObject(new Rectangle(img.getImageScaledWidth(), img.getImageScaledHeight()));
PdfCanvas pdfCanvas = new PdfCanvas(pdfFormXObject, pdfDoc);
try (Canvas canvas = new Canvas(pdfCanvas, pdfDoc, pdfFormXObject.getBBox().toRectangle())) {
    canvas.add(img);
}

BufferedReader br = new BufferedReader(new StringReader(text));
String line;
while ((line = br.readLine()) != null) {
    if("graph_add".equals(line)) {
        doc.add(new Image(pdfFormXObject));
    } else {
        doc.add(new Paragraph(line));
    }
}
doc.close();

（AddCanvasToDocument测试testAddCanvasForRuslan）

结果：

---

顺便说一句：如果在这个例子中只添加一个位图到Canvas，显然可以将Image img直接添加到Document doc而不是通过XObject形式......