java图片压缩详解编程语言

/**  
   * 改变图片的大小到宽为size，然后高随着宽等比例变化  
   * @param is 上传的图片的输入流  
   * @param os 改变了图片的大小后，把图片的流输出到目标OutputStream  
   * @param size 新图片的宽  
   * @param format 新图片的格式  
   * @throws IOException  
   */  
  public static void resizeImage1(InputStream is, OutputStream os, int size, String format) {   
      try { 
    BufferedImage prevImage = ImageIO.read(is);   
     double width = prevImage.getWidth();   
     double height = prevImage.getHeight();   
     double percent = size/width;   
     int newWidth = (int)(width * percent);   
     int newHeight = (int)(height * percent);   
     BufferedImage image = new BufferedImage(newWidth, newHeight, BufferedImage.TYPE_INT_BGR);   
     //以下代码在压缩图片透明背景会变成变黑色 
    /* Graphics graphics = image.createGraphics();   
     graphics.drawImage(prevImage, 0, 0, newWidth, newHeight, null);   
     ImageIO.write(image, format, os);*/   
     ///////////////////////////////////////// 
     
     //以下代码解决在压缩png格式的图片透明背景会变成变黑色的问题 
     Graphics2D g2d = image.createGraphics();  
     image = g2d.getDeviceConfiguration().createCompatibleImage(newWidth,newHeight,Transparency.TRANSLUCENT);  
        g2d.dispose();  
        g2d = image.createGraphics();  
        Image from = prevImage.getScaledInstance(newWidth, newHeight, prevImage.SCALE_AREA_AVERAGING);  
        g2d.drawImage(from, 0, 0, null); 
        g2d.dispose();  
        ImageIO.write(image, format,os);  
     os.flush();   
     is.close();   
     os.close();     } catch (Exception e) { 
    // TODO Auto-generated catch block 
    e.printStackTrace(); 
   }   
  }