IText 7 How To Add Div or Paragraph in Header Without Overlapping Page Content?

问题

I am facing the following problem for which i haven't found any solution yet. I am implementing a platform for a medical laboratory. They want for every incident to write the report to the system and then generate and print it from the system. I am using itext 7 to accomplish this. However i am facing the following problem.

They have a very strange template. On the first page in the beginning they want to print a specific table, while in the beginning of every other page they want to print something else. So i need to know when pages change in order to print in the beginning of the page the corresponding table.

After reading various sources i ended up creating the first page normally and then adding a header event handler that checks the page number and gets executed always except page 1.

public class VariableHeaderEventHandler implements IEventHandler {


    @Override
    public void handleEvent(Event event) {
        System.out.println("THIS IS ME: HEADER EVENT HANDLER STARTED.....");
        PdfDocumentEvent documentEvent = (PdfDocumentEvent) event;
        PdfDocument pdfDoc = documentEvent.getDocument();
        PdfPage page = documentEvent.getPage();
        Rectangle pageSize = page.getPageSize();
        int pageNumber = pdfDoc.getPageNumber(page);

        if (pageNumber == 1) return; //Do nothing in the first page...

        System.out.println("Page size: " + pageSize.getHeight());

        Rectangle rectangle = new Rectangle(pageSize.getLeft() + 30, pageSize.getHeight()-234, pageSize.getWidth() - 60, 200);


        PdfCanvas pdfCanvas = new PdfCanvas(page.newContentStreamBefore(), page.getResources(), pdfDoc);
        pdfCanvas.rectangle(rectangle);
        pdfCanvas.setFontAndSize(FontsAndStyles.getRegularFont(), 10);
        Canvas canvas = new Canvas(pdfCanvas, pdfDoc, rectangle);

        Div header = new Div();

        Paragraph paragraph = new Paragraph();

        Text text = new Text("Διαγνωστικό Εργαστήριο Ιστοπαθολογίας και Μοριακής Παθολογοανατομικής").addStyle(FontsAndStyles.getBoldStyle());
        paragraph.add(text);
        paragraph.add(new Text("\n"));
        text = new Text("Μοριακή Διάγνωση σε Συνεργασία με").addStyle(FontsAndStyles.getBoldStyle());
        paragraph.add(text);
        paragraph.add(new Text("\n"));
        text = new Text("Γκούρβας Βίκτωρας, M.D., Ph.D.").addStyle(FontsAndStyles.getBoldStyle());
        paragraph.add(text);
        paragraph.add(new Text("\n"));
        text = new Text("Τσιμισκή 33, Τ.Κ. 54624, ΘΕΣΣΑΛΟΝΙΚΗ").addStyle(FontsAndStyles.getNormalStyle());
        paragraph.add(text);
        paragraph.add(new Text("\n"));
        text = new Text("Τήλ/Φάξ: 2311292924 Κιν.: 6932104909 e-mail: vgourvas@gmail.com").addStyle(FontsAndStyles.getNormalStyle());
        paragraph.add(text);
        header.add(paragraph);

//        =============Horizontal Line BOLD============
        SolidLine solidLine = new SolidLine((float) 1.5);
        header.add(new LineSeparator(solidLine));
//        ========Horizontal Line BOLD End==========


        text = new Text("ΠΑΘΟΛΟΓΟΑΝΑΤΟΜΙΚΗ ΕΞΕΤΑΣΗ").addStyle(FontsAndStyles.getBoldStyle());
        paragraph = new Paragraph().add(text);


        header.add(paragraph);
        header.setTextAlignment(TextAlignment.CENTER);
        canvas.add(header);
        canvas.close();
    }

However the problem i am facing now is that header overlaps content and i can't figure out how to set different margins per page. For example form page 2 and beyond i would like different topMargin.

Has anyone faced these problems before and have found a working solution? Am I implementing correct? Is there a better way of accomplishing the same result?

Thanks in advance,

Toutoudakis Michail

回答1:

You should create your own custom document renderer and decrease the area which would be used to place content for each page except for the first one.

Please look at the snippet below and updateCurrentArea method in particular.

    class CustomDocumentRenderer extends DocumentRenderer {
    public CustomDocumentRenderer(Document document) {
        super(document);
    }

    @Override
    public IRenderer getNextRenderer() {
        return new CustomDocumentRenderer(this.document);
    }

    @Override
    protected LayoutArea updateCurrentArea(LayoutResult overflowResult) {
        LayoutArea area = super.updateCurrentArea(overflowResult);
        if (currentPageNumber > 1) {
            area.setBBox(area.getBBox().decreaseHeight(200));
        }  
        return area;
    }
}

Then just set the renderer on your document:

    Document doc = new Document(pdfDoc);
    doc.setRenderer(new CustomDocumentRenderer(doc));

The resultant pdf which I get for your document looks as follows:

There is another solution however. Once you've added at least one element to your document, you can change the default document's margins. The change will be applied on all pages created afterwards (and in your case these are pages 2, 3, ...)

        doc.add(new Paragraph("At least one element should be added. Otherwise the first page wouldn't be created and changing of the default margins would affect it."));
    doc.setMargins(200, 36, 36, 36);
    // now you can be sure that all the next pages would have new margins

来源：https://stackoverflow.com/questions/54439202/itext-7-how-to-add-div-or-paragraph-in-header-without-overlapping-page-content