如何在iText 7中添加页眉和页脚

在iText 7中添加页眉和页脚，可以通过自定义实现一个PdfPageEvent的子类来实现。以下是一个示例代码：

import com.itextpdf.kernel.events.Event;
import com.itextpdf.kernel.events.IEventHandler;
import com.itextpdf.kernel.events.PdfDocumentEvent;
import com.itextpdf.kernel.events.PdfPageEvent;
import com.itextpdf.kernel.geom.Rectangle;
import com.itextpdf.kernel.pdf.PdfDocument;
import com.itextpdf.kernel.pdf.PdfPage;
import com.itextpdf.kernel.pdf.canvas.PdfCanvas;
import com.itextpdf.layout.Canvas;
import com.itextpdf.layout.element.Paragraph;
import com.itextpdf.layout.property.TextAlignment;
import com.itextpdf.layout.property.VerticalAlignment;

public class HeaderFooterHandler implements IEventHandler {
    protected String header;
    protected String footer;

    public HeaderFooterHandler(String header, String footer) {
        this.header = header;
        this.footer = footer;
    }

    @Override
    public void handleEvent(Event event) {
        PdfDocumentEvent docEvent = (PdfDocumentEvent) event;
        PdfDocument pdfDoc = docEvent.getDocument();
        PdfPage page = docEvent.getPage();
        int pageNumber = pdfDoc.getPageNumber(page);

        Rectangle pageSize = page.getPageSize();
        PdfCanvas pdfCanvas = new PdfCanvas(page.newContentStreamBefore(), page.getResources(), pdfDoc);

        // 添加页眉
        Canvas canvas = new Canvas(pdfCanvas, pdfDoc, pageSize);
        canvas.showTextAligned(new Paragraph(header), pageSize.getLeft() + 40, pageSize.getTop() - 30, TextAlignment.LEFT, VerticalAlignment.MIDDLE);

        // 添加页脚
        canvas.showTextAligned(new Paragraph(footer + " - " + pageNumber), pageSize.getRight() - 40, pageSize.getBottom() + 30, TextAlignment.RIGHT, VerticalAlignment.MIDDLE);

        pdfCanvas.release();
    }
}

然后，在创建PDF文档时，将自定义的HeaderFooterHandler实例添加到PdfDocument中：

import com.itextpdf.kernel.pdf.PdfWriter;
import com.itextpdf.layout.Document;

public class AddHeaderFooterExample {
    public static void main(String[] args) {
        String header = "这是页眉";
        String footer = "这是页脚";

        PdfDocument pdfDoc = new PdfDocument(new PdfWriter("output.pdf"));
        Document doc = new Document(pdfDoc);

        // 添加页眉和页脚处理器
        pdfDoc.addEventHandler(PdfDocumentEvent.START_PAGE, new HeaderFooterHandler(header, footer));

        // 添加内容到PDF文档
        doc.add(new Paragraph("这是第一页的内容"));
        doc.add(new AreaBreak());
        doc.add(new Paragraph("这是第二页的内容"));

        doc.close();
    }
}

这样，生成的PDF文档中每一页都会有相应的页眉和页脚。你可以根据需要自定义页眉和页脚的内容和样式。