itext7导出pdf的分页，添加页眉，页脚的Java代码

下面是使用itext7导出pdf，添加分页、页眉和页脚的Java代码示例：

import com.itextpdf.kernel.pdf.PdfDocument;
import com.itextpdf.kernel.pdf.PdfPage;
import com.itextpdf.kernel.pdf.PdfWriter;
import com.itextpdf.layout.Document;
import com.itextpdf.layout.element.Paragraph;
import com.itextpdf.layout.element.Text;
import com.itextpdf.layout.renderer.DocumentRenderer;
import com.itextpdf.layout.renderer.DrawContext;
import com.itextpdf.layout.renderer.IRenderer;

import java.io.File;
import java.io.FileNotFoundException;
import java.util.ArrayList;
import java.util.List;

public class PdfGenerator {

    private static final String DEST = "output.pdf";

    public static void main(String[] args) throws FileNotFoundException {
        File file = new File(DEST);
        file.getParentFile().mkdirs();
        new PdfGenerator().createPdf(DEST);
    }

    public void createPdf(String dest) throws FileNotFoundException {
        PdfWriter writer = new PdfWriter(dest);
        PdfDocument pdf = new PdfDocument(writer);
        Document document = new Document(pdf);

        // 设置页眉和页脚
        pdf.addEventHandler(PdfDocumentEvent.START_PAGE, new PageEventHandler());

        // 添加内容
        List<String> paragraphs = new ArrayList<>();
        paragraphs.add("Paragraph 1");
        paragraphs.add("Paragraph 2");
        paragraphs.add("Paragraph 3");
        paragraphs.add("Paragraph 4");
        paragraphs.add("Paragraph 5");
        paragraphs.add("Paragraph 6");
        paragraphs.add("Paragraph 7");
        paragraphs.add("Paragraph 8");
        paragraphs.add("Paragraph 9");
        paragraphs.add("Paragraph 10");

        for (String text : paragraphs) {
            document.add(new Paragraph(text));
        }

        document.close();
    }

    // 实现分页、页眉和页脚
    private static class PageEventHandler implements IPdfPageEvent {

        @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);
            Canvas canvas = new Canvas(pdfCanvas, pdfDoc, pageSize);

            // 添加页眉
            canvas.showTextAligned(new Paragraph("Header").setFontColor(Color.GRAY), pageSize.getWidth() / 2, pageSize.getTop() - 30, TextAlignment.CENTER);

            // 添加页脚
            canvas.showTextAligned(new Paragraph(String.format("Page %d", pageNumber)), pageSize.getWidth() / 2, pageSize.getBottom() + 30, TextAlignment.CENTER);

            canvas.close();
        }
    }

    // 实现分页
    private static class CustomRenderer extends DocumentRenderer {
        public CustomRenderer(Document document) {
            super(document);
        }

        @Override
        public void drawBackground(DrawContext drawContext) {
            super.drawBackground(drawContext);
            int pageNumber = getCurrentArea().getPageNumber();
            if (pageNumber != 1) {
                drawContext.getCanvas().beginText().setFontAndSize(PdfFontFactory.createFont(), 12).moveText(36, 20).showText(String.valueOf(pageNumber)).endText();
            }
        }

        @Override
        public IRenderer getNextRenderer() {
            return new CustomRenderer(getDocument());
        }
    }
}

在上面的代码中，我们首先创建一个 `PdfWriter` 和 `PdfDocument`。然后我们创建一个 `Document` 并设置页眉和页脚的代码。我们添加了一些段落到文档中。

我们使用了 `PageEventHandler` 实现了分页、页眉和页脚。在 `handleEvent` 方法中，我们获取了当前页码，并添加了页眉和页脚。

我们还使用了 `CustomRenderer` 实现了分页。在 `drawBackground` 方法中，我们将当前页码添加到每一页的左下角。