java圖片壓縮

/**


改變圖片的大小到寬為size，然后高隨著寬等比例變化 
@param is 上傳的圖片的輸入流 
@param os 改變了圖片的大小后，把圖片的流輸出到目標OutputStream 
@param size 新圖片的寬 
@param format 新圖片的格式 
@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);

//以下代碼在壓縮圖片透明背景會變成變黑色
/ Graphics graphics = image.createGraphics();

graphics.drawImage(prevImage, 0, 0, newWidth, newHeight, null);

ImageIO.write(image, format, os);*/

/////////////////////////////////////////
//以下代碼解決在壓縮png格式的圖片透明背景會變成變黑色的問題
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();
}

}  </pre>