与您现在的代码相比，需要做更多的工作，因为一旦将元素添加到文档中，对元素的更改就不会生效。立即刷新设置为 false 允许您重新布局元素，但这不会自动发生。您计算段落将放置在的当前页面 (int numberOfPages = pdfDocument.getNumberOfPages();) 的方式不是防弹的，因为在某些情况下可能会提前添加页面，即使内容不会立即放置在它们上。
有一种非常低级的方法可以实现您的目标，但是对于最新版本的 iText (7.1.15)，还有一种更简单的方法，但仍然需要一些工作。基本上，您的用例与 CSS 中的 target-counter 概念非常相似，page 计数器是您案例中的目标。为了支持 pdfHTML 插件中的目标计数器，我们在 layout 模块中添加了新功能，这些功能也可以直接使用。
首先，我们要将Link 元素与它们将指向的相应Paragraph 元素联系起来。我们将在布局中使用ID 属性：
link.setProperty(Property.ID, String.valueOf(count));
noteText.setProperty(Property.ID, String.valueOf(count));
接下来，我们将为Link 元素和Paragraph 元素创建自定义渲染器。这些自定义渲染器将与TargetCounterHandler 交互，这是我在介绍中提到的layout 模块中的新功能。这个想法是，在布局操作期间，段落将记住放置它的页面，然后相应的链接元素（请记住，链接元素连接到段落元素）将在该链接元素的布局过程中询问TargetCounterHandler计划了相应的段落。所以在某种程度上，TargetCounterHandler 是一个连接器。
自定义渲染器代码：
private static class CustomParagraphRenderer extends ParagraphRenderer {
public CustomParagraphRenderer(Paragraph modelElement) {
super(modelElement);
}
@Override
public IRenderer getNextRenderer() {
return new CustomParagraphRenderer((Paragraph) modelElement);
}
@Override
public LayoutResult layout(LayoutContext layoutContext) {
LayoutResult result = super.layout(layoutContext);
TargetCounterHandler.addPageByID(this);
return result;
}
}
private static class CustomLinkRenderer extends LinkRenderer {
public CustomLinkRenderer(Link link) {
super(link);
}
@Override
public LayoutResult layout(LayoutContext layoutContext) {
Integer targetPageNumber = TargetCounterHandler.getPageByID(this, getProperty(Property.ID));
if (targetPageNumber != null) {
setText(String.valueOf(targetPageNumber));
}
return super.layout(layoutContext);
}
@Override
public IRenderer getNextRenderer() {
return new CustomLinkRenderer((Link) getModelElement());
}
}
不要忘记将自定义渲染器分配给他们的元素：
link.setNextRenderer(new CustomLinkRenderer(link));
noteText.setNextRenderer(new CustomParagraphRenderer(noteText));
现在，我们需要做的另一件事relayout。您已经将immediateFlush 设置为false，这是relayout 工作所必需的。需要重新布局，因为在第一个布局循环中，我们不会知道段落的所有位置，但是当我们知道这些位置时，我们已经在页面上放置了链接。因此，我们需要第二次传递来使用有关段落所在页码的信息，并将该信息设置为链接。
Relayout 非常简单 - 一旦您放置了所有内容，您只需要调用一个专用方法即可：
// For now we have to prepare the handler for relayout manually, this is going to be improved
// in future iText versions
((DocumentRenderer)document.getRenderer()).getTargetCounterHandler().prepareHandlerToRelayout();
document.relayout();
需要注意的是，现在您还需要对DocumentRenderer 进行子类化，因为还有一个额外的操作需要在后台执行 - 将目标计数器处理程序传播到根渲染器，我们将用于第二个布局操作：
// For now we have to create a custom renderer for the root document to propagate the
// target counter handler to the renderer that will be used on the second layout process
// This is going to be improved in future iText versions
private static class CustomDocumentRenderer extends DocumentRenderer {
public CustomDocumentRenderer(Document document, boolean immediateFlush) {
super(document, immediateFlush);
}
@Override
public IRenderer getNextRenderer() {
CustomDocumentRenderer renderer = new CustomDocumentRenderer(document, immediateFlush);
renderer.targetCounterHandler = new TargetCounterHandler(targetCounterHandler);
return renderer;
}
}
document.setRenderer(new CustomDocumentRenderer(document, false));
现在我们完成了。这是我们的视觉结果：
完整代码如下：
public class UpdateLinkTest {
PdfDocument pdfDocument = null;
Color hyperlinkColor = new DeviceRgb(0, 102, 204);
public static void main(String[] args) throws Exception {
List<String[]> notes = new ArrayList<>();
notes.add(new String[] {"me", "title", "this is my text" });
notes.add(new String[] {"me2", "title2", "this is my text 2" });
new UpdateLinkTest().exportPdf(notes, new File("./test2.pdf"));
}
public void exportPdf(List<String[]> notes, File selectedFile) throws Exception {
PdfWriter pdfWriter = new PdfWriter(selectedFile);
pdfDocument = new PdfDocument(pdfWriter);
Document document = new Document(pdfDocument, PageSize.A4, false);
document.setRenderer(new CustomDocumentRenderer(document, false));
// add the table of contents table
addSummaryTable(notes, document);
// add a page break
document.add(new AreaBreak(AreaBreakType.NEXT_PAGE));
// add the body of the document
addNotesText(notes, document);
// For now we have to prepare the handler for relayout manually, this is going to be improved
// in future iText versions
((DocumentRenderer)document.getRenderer()).getTargetCounterHandler().prepareHandlerToRelayout();
document.relayout();
document.close();
}
private void addSummaryTable(List<String[]> notes, Document document) {
Table table = new Table(3);
float pageWidth = PageSize.A4.getWidth();
table.setWidth(pageWidth-document.getLeftMargin()*2);
// add header
addCell("Author", table, true);
addCell("Title", table, true);
addCell("Page", table, true);
int count = 0;
for (String[] note : notes) {
addCell(note[0], table, false);
addCell(note[1], table, false);
Link link = new Link("Go!", PdfAction.createGoTo(""+ (count+1)));
link.setProperty(Property.ID, String.valueOf(count));
link.setNextRenderer(new CustomLinkRenderer(link));
addCell(link, hyperlinkColor, table, false);
count++;
}
document.add(table);
}
private void addNotesText(List<String[]> notes, Document document) {
int count = 0;
for (String[] note : notes) {
Paragraph noteText = new Paragraph(note[2]);
noteText.setProperty(Property.ID, String.valueOf(count));
noteText.setNextRenderer(new CustomParagraphRenderer(noteText));
document.add(noteText);
noteText.setDestination(++count+"");
if (note != notes.get(notes.size()-1))
document.add(new AreaBreak(AreaBreakType.NEXT_PAGE));
}
}
private static void addCell(String text, Table table, boolean b) {
Cell c1 = new Cell().add(new Paragraph(text));
table.addCell(c1);
}
private static void addCell(Link text, Color backgroundColor, Table table, boolean b) {
Cell c1 = new Cell().add(new Paragraph(text));
text.setUnderline();
text.setFontColor(backgroundColor);
table.addCell(c1);
}
private static class CustomLinkRenderer extends LinkRenderer {
public CustomLinkRenderer(Link link) {
super(link);
}
@Override
public LayoutResult layout(LayoutContext layoutContext) {
Integer targetPageNumber = TargetCounterHandler.getPageByID(this, getProperty(Property.ID));
if (targetPageNumber != null) {
setText(String.valueOf(targetPageNumber));
}
return super.layout(layoutContext);
}
@Override
public IRenderer getNextRenderer() {
return new CustomLinkRenderer((Link) getModelElement());
}
}
private static class CustomParagraphRenderer extends ParagraphRenderer {
public CustomParagraphRenderer(Paragraph modelElement) {
super(modelElement);
}
@Override
public IRenderer getNextRenderer() {
return new CustomParagraphRenderer((Paragraph) modelElement);
}
@Override
public LayoutResult layout(LayoutContext layoutContext) {
LayoutResult result = super.layout(layoutContext);
TargetCounterHandler.addPageByID(this);
return result;
}
}
// For now we have to create a custom renderer for the root document to propagate the
// target counter handler to the renderer that will be used on the second layout process
// This is going to be improved in future iText versions
private static class CustomDocumentRenderer extends DocumentRenderer {
public CustomDocumentRenderer(Document document, boolean immediateFlush) {
super(document, immediateFlush);
}
@Override
public IRenderer getNextRenderer() {
CustomDocumentRenderer renderer = new CustomDocumentRenderer(document, immediateFlush);
renderer.targetCounterHandler = new TargetCounterHandler(targetCounterHandler);
return renderer;
}
}
}