看了一些网上的代码，总觉得，是在计算机出长和宽，起始坐标后 裁减了原图片，到底能不能实现压缩，比如：原图的大小为 310*330 我现在想把长固定为220然后宽压缩为 220/310*330 的效果？
jmagick ( http://www.jmagick.org/index.html )，imagemagick的Java实现。可以用
php的GD库毫无压力的做到……imagemagick当然也行了，其java实现就是@gaosboy所说的jmagick拉。
用imagemagick的效果好。不过用起来不是很方便。在linux下倒还方便。在win下用就没那么方便了。
对效果要求不高可以用awt来缩放就可以了。
public final class ThumbUtils {
private ThumbUtils() {
}
/**
* @param in
* @param out
* @param formatName
* @param size
* @throws IOException
*/
public static void encodeThumb(InputStream in, OutputStream out, PictureSize limitSize, String formatName) throws IOException {
BufferedImage image = ImageIO.read(in);
encodeThumb(image, out, limitSize, formatName);
}
public static void encodeThumb(BufferedImage image, OutputStream out, PictureSize limitSize, String formatName) throws IOException {
PictureSize originalSize = new PictureSize(image.getWidth(null), image.getHeight(null));
PictureSize thumbSize = getThumbSize(limitSize, originalSize);
int width = thumbSize.getWidth(), height = thumbSize.getHeight();
ColorModel dstCM = image.getColorModel();
BufferedImage dst = new BufferedImage(dstCM, dstCM.createCompatibleWritableRaster(width, height), dstCM.isAlphaPremultiplied(), null);
Image scaleImage = image.getScaledInstance(width, height, Image.SCALE_SMOOTH);
Graphics2D g = dst.createGraphics();
g.drawImage(scaleImage, 0, 0, width, height, null);
g.dispose();
ImageIO.write(dst, formatName, out);
}
/**
* @param limitSize
* @param originalSize
* @return
*/
public static PictureSize getThumbSize(PictureSize limitSize, PictureSize originalSize) {
int maxWidth = limitSize.getWidth();
int maxHeight = limitSize.getHeight();
if (maxWidth == 0 && maxHeight == 0) {
maxWidth = maxHeight = DEFAULT_THUMB_SIZE;
}
int originalWidth = originalSize.getWidth();
int originalHeight = originalSize.getHeight();
int width = DEFAULT_THUMB_SIZE, height = DEFAULT_THUMB_SIZE;
float rate = 0;
if (maxWidth > 0 && maxHeight > 0) {
rate = Math.min(maxWidth * 1f / originalWidth, maxHeight * 1f / originalHeight);
} else if (maxWidth > 0) {
rate = maxWidth * 1f / originalWidth;
} else if (maxHeight > 0) {
rate = maxHeight * 1f / originalHeight;
} else {
// no happen.
}
width = (int) (originalWidth * rate);
height = (int) (originalHeight * rate);
return new PictureSize(width, height);
}
public static final int DEFAULT_THUMB_SIZE = 96;
}淘宝网使用GraphicsMagick处理图片，据说比imagemagick更高效，Java API：im4java。
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