iText生成PDF文件，每页显示页码以及总页数的实现

如果想在页眉或者页脚加上第x页这样的信息，用普通的HeaderFooter就能轻松搞定。

HeaderFooter footer = new HeaderFooter(new Phrase("第：",FontChinese), new Phrase("页",FontChinese));    
footer.setBorder(Rectangle.NO_BORDER);  
document.setFooter(footer);  
document.open();

如果想在每页显示第x页/共y页这样的功能，实现起来没有那么轻松。
官方页面有具体实现的例子，连接地址：
http://itextdocs.lowagie.com/tutorial/directcontent/pageevents/index.php
源码：
http://itextdocs.lowagie.com/examples/com/lowagie/examples/directcontent/pageevents/PageNumbersWatermark.java

源码里面的东西比较繁多，精简以后如下：

import java.io.FileOutputStream;

import com.lowagie.text.Document;
import com.lowagie.text.Element;
import com.lowagie.text.ExceptionConverter;
import com.lowagie.text.Font;
import com.lowagie.text.PageSize;
import com.lowagie.text.Paragraph;
import com.lowagie.text.pdf.BaseFont;
import com.lowagie.text.pdf.PdfContentByte;
import com.lowagie.text.pdf.PdfPageEventHelper;
import com.lowagie.text.pdf.PdfTemplate;
import com.lowagie.text.pdf.PdfWriter;

public class PdfExport extends PdfPageEventHelper{
	
	public PdfTemplate tpl;
	public BaseFont bf;

	public static void main(String[] args) {
		Document document = new Document(PageSize.A4, 20, 20, 20, 20);
		try {			
			PdfWriter writer = PdfWriter.getInstance(document, new FileOutputStream("D:\\HelloItext.pdf"));
			writer.setPageEvent(new PdfExport());
			
			BaseFont bfChinese = BaseFont.createFont("STSong-Light", "UniGB-UCS2-H", BaseFont.NOT_EMBEDDED);
	
			document.open();
			
			Paragraph title = new Paragraph("测试内容。。。。", new Font(bfChinese,15));
			title.setAlignment(Element.ALIGN_CENTER);
			document.add(title);	
		} catch (Exception de) {
			de.printStackTrace();
		}
		document.close();
	}
	
	public void onOpenDocument(PdfWriter writer, Document document) {
        try {
            tpl = writer.getDirectContent().createTemplate(100, 100);
            bf = BaseFont.createFont("STSong-Light", "UniGB-UCS2-H", BaseFont.NOT_EMBEDDED);   
        }
        catch(Exception e) {
            throw new ExceptionConverter(e);
        }
    }
    
    public void onEndPage(PdfWriter writer, Document document) {
       //在每页结束的时候把“第x页”信息写道模版指定位置
        PdfContentByte cb = writer.getDirectContent();
        cb.saveState();
        String text = "第" + writer.getPageNumber() + "页,共";
        cb.beginText();
        cb.setFontAndSize(bf, 8);
        cb.setTextMatrix(460, 786);//定位“第x页,共” 在具体的页面调试时候需要更改这xy的坐标
        cb.showText(text);
        cb.endText();
        cb.addTemplate(tpl, 492, 786);//定位“y页” 在具体的页面调试时候需要更改这xy的坐标

        cb.saveState();
        cb.stroke();
        cb.restoreState();       
        cb.closePath();//sanityCheck();
    }
    
    public void onCloseDocument(PdfWriter writer, Document document) {
       //关闭document的时候获取总页数，并把总页数按模版写道之前预留的位置
       tpl.beginText();
       tpl.setFontAndSize(bf, 8);
       tpl.showText(Integer.toString(writer.getPageNumber() - 1)+"页");
       tpl.endText();
       tpl.closePath();//sanityCheck();
    }
}