java实现给pdf文件加水印！

给pdf文档加水印！

import java.awt.Color;
import java.io.BufferedOutputStream;
import java.io.File;
import java.io.FileOutputStream;
import java.io.IOException;
import java.text.SimpleDateFormat;
import java.util.Calendar;

import com.lowagie.text.DocumentException;
import com.lowagie.text.Element;
import com.lowagie.text.Image;
import com.lowagie.text.pdf.BaseFont;
import com.lowagie.text.pdf.PdfContentByte;
import com.lowagie.text.pdf.PdfGState;
import com.lowagie.text.pdf.PdfReader;
import com.lowagie.text.pdf.PdfStamper;

	
public static void waterMark(String inputFile,    
            String outputFile, String waterMarkName) {    
        try {    
            PdfReader reader = new PdfReader(inputFile);    
            PdfStamper stamper = new PdfStamper(reader, new FileOutputStream(    
                    outputFile));    
              
            BaseFont base = BaseFont.createFont("STSong-Light", "UniGB-UCS2-H",   BaseFont.EMBEDDED);  
              
            Rectangle pageRect = null;  
            PdfGState gs = new PdfGState();  
            gs.setFillOpacity(0.3f);  
            gs.setStrokeOpacity(0.4f);  
            int total = reader.getNumberOfPages() + 1;   
              
            JLabel label = new JLabel();  
            FontMetrics metrics;  
            int textH = 0;   
            int textW = 0;   
            label.setText(waterMarkName);   
            metrics = label.getFontMetrics(label.getFont());   
            textH = metrics.getHeight();
            textW = metrics.stringWidth(label.getText());  
                
            PdfContentByte under;    
            for (int i = 1; i < total; i++) {   
            	under = stamper.getOverContent(i);// 在内容上方加水印
			    //content = stamper.getUnderContent(i);//在内容下方加水印
				gs.setFillOpacity(0.2f);
				// content.setGState(gs);
				under.beginText();
				 
				under.setFontAndSize(base, 50);
				under.setTextMatrix(70, 200);
				under.showTextAligned(Element.ALIGN_CENTER, "测试水印！", 300,350, 55); 
              
                
                
                under.endText();  
            }   
          
          //一定不要忘记关闭流
            stamper.close();  
            reader.close();
        } catch (Exception e) {    
            e.printStackTrace();    
        }    
    }