BufferedImage image= bim;//二维码
BufferedImage bg= ImageIO.read(路径);//获取北京图片
Graphics2D g=bg.createGraphics();
int width=image.getWidth(null) > bg.getWidth() * 5/10? (bg.getWidth() * 5/10) : image.getWidth(null);
int height=image.getHeight(null) > bg.getHeight() *5 /10? (bg.getHeight() * 5/10) : image.getWidth(null);
g.drawImage(image,(bg.getWidth()- width)/2,(bg.getHeight()-height)/2,width,height,null);
g.dispose();
bg.flush();
image.flush();
ImageIO.write(bg,"png", file);