In iText 7 java how do you update Link text after it's already been added to the document - itext

Question

I am using iText7 to build a table of contents for my document. I know all the section names before I start, but don't know what the page numbers will be. My current process is to create a table on the first page and create all the Link objects with generic text "GO!". Then as I add sections I add through the link objects and update the text with the page numbers that I figured out as I created the document.
However, at the end, what gets written out for the link is "GO!", not the updated page number values I set as I was creating the rest of the document.
I did set the immediateFlush flag to false when I created the Document.
public class UpdateLinkTest {
PdfDocument pdfDocument = null;
List<Link>links = 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);
// 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);
document.close();
}
private void addSummaryTable(List<String[]> notes, Document document) {
links = new ArrayList<>();
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)));
links.add(link);
addCell(link, hyperlinkColor, table, false);
count++;
}
document.add(table);
}
private void addNotesText(List<String[]> notes, Document document)
throws Exception {
int count = 0;
for (String[] note : notes) {
int numberOfPages = pdfDocument.getNumberOfPages();
Link link = links.get(count);
link.setText(""+(numberOfPages+1));
Paragraph noteText = new Paragraph(note[2]);
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);
}
}

Answer 1

Quite more work needs to be done compared to the code you have now because the changes to the elements don't take any effect once you've added them to the document. Immediate flush set to false allows you to relayout the elements, but that does not happen automatically. The way you calculate the current page the paragraph will be placed on (int numberOfPages = pdfDocument.getNumberOfPages();) is not bulletproof because in some cases pages might be added in advance, even if the content is not going to be placed on them immediately.
There is a very low level way to achieve your goal but with the recent version of iText (7.1.15) there is a simpler way as well, which still requires some work though. Basically your use case is very similar to target-counter concept in CSS, with page counter being the target one in your case. To support target counters in pdfHTML add-on we added new capabilities to our layout module which are possible to use directly as well.
To start off, we are going to tie our Link elements to the corresponding Paragraph elements that they will point to. We are going to do it with ID property in layout:
link.setProperty(Property.ID, String.valueOf(count));
noteText.setProperty(Property.ID, String.valueOf(count));
Next up, we are going to create custom renderers for our Link elements and Paragraph elements. Those custom renderers will interact with TargetCounterHandler which is the new capability in layout module I mentioned in the introduction. The idea is that during layout operation the paragraph will remember the page on which it was placed and then the corresponding link element (remember, link elements are connected to paragraph elements) will ask TargetCounterHandler during layout process of that link element which page the corresponding paragraph was planed on. So in a way, TargetCounterHandler is a connector.
Code for custom renderers:
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());
}
}
Don't forget to assign the custom renderers to their elements:
link.setNextRenderer(new CustomLinkRenderer(link));
noteText.setNextRenderer(new CustomParagraphRenderer(noteText));
Now, the other thing we need to do it relayout. You already set immediateFlush to false and this is needed for relayout to work. Relayout is needed because on the first layout loop we will not know all the positions of the paragraphs, but we will already have placed the links on the pages by the time we know those positions. So we need the second pass to use the information about page numbers the paragraphs will reside on and set that information to the links.
Relayout is pretty straightforward - once you've put all the content you just need to call a single dedicated method:
// 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();
One caveat is that for now you also need to subclass the DocumentRenderer since there is an additional operation that needs to be done that is not performed under the hood - propagation of the target counter handler to the root renderer we will be using for the second layout operation:
// 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));
And now we are done. Here is our visual result:
Complete code looks as follows:
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;
}
}
}