java 图片如何让白色变透明

import  java.awt.Graphics2D;
import  java.awt.image.BufferedImage;
import  java.io.File;
import  java.io.IOException;
import  java.util.regex.Pattern;

import  javax.imageio.ImageIO;
import  javax.swing.ImageIcon;
import  javax.swing.JOptionPane;

public  class  Picture {

    public  static  void  convert(String path) {
        // TODO Auto-generated constructor stub
        try  {
            BufferedImage image = ImageIO.read( new  File(path));
            ImageIcon imageIcon =  new  ImageIcon(image);
            BufferedImage bufferedImage =  new  BufferedImage(
                    imageIcon.getIconWidth(), imageIcon.getIconHeight(),
                    BufferedImage.TYPE_4BYTE_ABGR);
            Graphics2D g2D = (Graphics2D) bufferedImage.getGraphics();
            g2D.drawImage(imageIcon.getImage(),  0 ,  0 ,
                    imageIcon.getImageObserver());
            int  alpha =  0 ;
            for  ( int  j1 = bufferedImage.getMinY(); j1 < bufferedImage
                    .getHeight(); j1++) {
                for  ( int  j2 = bufferedImage.getMinX(); j2 < bufferedImage
                        .getWidth(); j2++) {
                    int  rgb = bufferedImage.getRGB(j2, j1);
                    if  (colorInRange(rgb))
                        alpha =  0 ;
                    else
                        alpha =  255 ;
                    rgb = (alpha <<  24 ) | (rgb &  0x00ffffff );
                    bufferedImage.setRGB(j2, j1, rgb);
                }
            }
            g2D.drawImage(bufferedImage,  0 ,  0 , imageIcon.getImageObserver());
            // 生成图片为PNG
            String outFile = path.substring( 0 , path.lastIndexOf( "." ));
            ImageIO.write(bufferedImage,  "png" ,  new  File(outFile +  ".png" ));
        }  catch  (IOException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }
    }

    public  static  boolean  colorInRange( int  color) {
        int  red = (color &  0xff0000 ) >>  16 ;
        int  green = (color &  0x00ff00 ) >>  8 ;
        int  blue = (color &  0x0000ff );
        if  (red >= color_range && green >= color_range && blue >= color_range)
            return  true ;
        return  false ;
    }

    public  static  int  color_range =  210 ;
    public  static  Pattern pattern = Pattern.compile( "[0-9]*" );

    public  static  boolean  isNo(String str) {
        return  pattern.matcher(str).matches();
    }

    /**
     * @param args
     */
    public  static  void  main(String[] args) {
        // TODO Auto-generated method stub
        String path = JOptionPane.showInputDialog( null ,  "请输入图片目录" );
        if  (path ==  null  || ! new  File(path).isDirectory()) {
            JOptionPane.showMessageDialog( null ,  "输入目录有误！" );
            return ;
        }
        String color = JOptionPane.showInputDialog( null ,  "请输入色差范围0~255(建议10~50)" );
        if  (isNo(color)) {
            color_range =  255  - Integer.parseInt(color);
            File file =  new  File(path);
            String[] files = file.list();
            for  ( int  i =  0 ; i < files.length; i++) {
                String ext = files[i].substring(files[i].lastIndexOf( "." ) +  1 );
                if  (ext.equals( "jpg" )) {
                    convert(path +  "//"  + files[i]);
                }
            }
            JOptionPane.showMessageDialog( null ,  "转换完成！" );
        }  else  {
            JOptionPane.showMessageDialog( null ,  "输入的数字有误！" );
        }
    }

}