如何使用Java和itext从Graphics对象创建包含多个页面的PDF

2 years ago

document.open();

    // the same contentByte is returned, it's just flushed & reset during
    // new page events.
    PdfContentByte cb = writer.getDirectContent();

    for (int _pageNumber = 0; _pageNumber < _numberofPages; ++_numberOfPages) {
      /*******************/
      //harmless in first pass, *necessary* in others
      document.newPage(); 
      /*******************/

      g2 = cb.createGraphics(_pageWidth, _height);
      g2.translate(0, (_numberOfPages - _pageNumber) * _pageHeight);
      draw(g2);
      g2.dispose();
    }

    document.close();

因此，您将整个界面渲染N次，并且仅在不同位置显示页面大小的切片 . 这在印刷世界IIRC中被称为“条带化” . 聪明，但它在PDF中可能更有效率 .

将整个界面渲染为一个巨大的PdfTemplate（使用g2d），一次 . 然后将该模板绘制到所有页面中，使得您想要的部分在当前页面的边距内可见（“媒体框”） .

PdfContentByte cb = writer.getDirectContent();
float entireHeight = _numberOfPages * _pageHeight;
PdfTemplate hugeTempl = cb.createTemplate( 0, -entireHeight, pageWidth, _pageHeight );
g2 = hugeTempl.createGraphics(0, -entireHeight, _pageWidth, _pageHeight ); 
draw(g2);
g2.dispose();

for (int curPg = 0; curPg < _numberOfPages; ++curPg) {
  cb.addTemplateSimple( hugeTempl, 0, -_pageHeight * curPg );

  document.newPage();
}

PDF的坐标空间在左下角设置为0,0，当您向上和向右时，这些值会增加 . PdfGraphis2D做了相当多的魔术来隐藏与你的区别，但我们仍然需要在这里处理它...因此在边界框和绘图位置中的负坐标 .

这完全是“背面的卫生巾”编码，我完全有可能在那里犯了一两个错误......但这就是主意 .

2 years ago

我在遵循上面的代码时遇到了麻烦（某些方法在当前的itextpdf版本中似乎有所改变） . 这是我的解决方案：

import com.itextpdf.awt.PdfGraphics2D;
import com.itextpdf.text.Document;
import com.itextpdf.text.PageSize;
import com.itextpdf.text.pdf.PdfContentByte;
import com.itextpdf.text.pdf.PdfTemplate;
import com.itextpdf.text.pdf.PdfWriter;
import java.awt.Color;
import java.awt.Dimension;
import java.awt.Graphics2D;
import java.awt.event.WindowEvent;
import java.io.FileOutputStream;
import java.io.OutputStream;
import javax.swing.JFrame;
import javax.swing.JLabel;
import javax.swing.JPanel;
import net.miginfocom.swing.MigLayout;

public class PanelToPDF {

    private static JFrame frame= new JFrame();
    private static JPanel view= new JPanel();
    private static float pageWidth= PageSize.A4.getWidth();
    private static float pageHeight= PageSize.A4.getHeight();

    public static void main(String[] args) throws Exception {
        System.out.println("Page width = " + pageWidth + ", height = " + pageHeight);

        initPane();
        createMultipagePDF();

        frame.dispatchEvent(new WindowEvent(frame, WindowEvent.WINDOW_CLOSING));
    }


    private static void initPane() {
        view.setLayout(new MigLayout());
        view.setBackground(Color.WHITE);

        for (int i= 1; i <= 160; ++i) {
            JLabel label= new JLabel("This is a test! " + i);
            label.setForeground(Color.BLACK);
            view.add(label, "wrap");

            JPanel subPanel= new JPanel();
            subPanel.setBackground(Color.RED);
            view.add(subPanel);
        }

        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        frame.setSize(new Dimension(Math.round(pageWidth), Math.round(pageHeight)));
        frame.add(view);
        frame.setVisible(true);
    }

    private static void createMultipagePDF() throws Exception {
        // Calculate the number of pages required. Use the preferred size to get
        // the entire panel height, rather than the panel height within the JFrame
        int numPages= (int) Math.ceil(view.getPreferredSize().height / pageHeight); // int divided by float

        // Output to PDF
        OutputStream os= new FileOutputStream("test.pdf");
        Document doc= new Document();
        PdfWriter writer= PdfWriter.getInstance(doc, os);
        doc.open();
        PdfContentByte cb= writer.getDirectContent();

        // Iterate over pages here
        for (int currentPage= 0; currentPage < numPages; ++currentPage) {
            doc.newPage(); // not needed for page 1, needed for >1

            PdfTemplate template= cb.createTemplate(pageWidth, pageHeight);
            Graphics2D g2d= new PdfGraphics2D(template, pageWidth, pageHeight * (currentPage + 1));
            view.printAll(g2d);
            g2d.dispose();

            cb.addTemplate(template, 0, 0);
        }

        doc.close();
    }