Thumbnails.of(src).size(100,100).keepAspectRatio(false).toFile(desc) 

Thumbnails.of(src).forceSize(100,100).toFile(desc)

<dependency>
<groupId>net.coobird</groupId>
<artifactId>thumbnailator</artifactId>
<version>0.4.8</version>
</dependency>

//保持图片不变形，多余部分裁剪掉
//压缩至指定图片尺寸（例如：横400高300）
BufferedImage image = ImageIO.read(fromPic); 
Builder builder = null; 
int imageWidth = image.getWidth(); 
int imageHeitht = image.getHeight(); 
if ((float)300 / 400 != (float)imageWidth / imageHeitht) { 
if (imageWidth > imageHeitht) { 
image = Thumbnails.of(fromPic).height(300).asBufferedImage(); 
} 
else { 
image = Thumbnails.of(fromPic).width(400).asBufferedImage();
 } 
builder = Thumbnails.of(image).sourceRegion(Positions.CENTER, 400, 300).size(400, 300);
 } else {
 builder = Thumbnails.of(image).size(400, 300);
} 
builder.outputFormat("jpg").toFile(toPic); //注意：scale、width|height、size三者不能同时共存，但必须要有一个

//asBufferedImage() 返回BufferedImage  
BufferedImage thumbnail = Thumbnails.of("images/a380_1280x1024.jpg")   
        .size(1280, 1024)  
        .toOutputStream(response.getOutputStream());