图片问题

一、用Thumbnails工具类实现
二、文件流实现
图片尺寸不变，质量改变
public static File resize(Float quality, File file, Image targetImage) throws ImageFormatException, IOException {
    int newWidth = targetImage.getWidth(null);
        int newHeight = targetImage.getHeight(null);
        ImageWriter imgWrier; 
        ImageWriteParam imgWriteParams; 
 
        // 指定写图片的方式为 jpg 
        imgWrier = ImageIO.getImageWritersByFormatName("png").next(); 
      imgWriteParams = new JPEGImageWriteParam(null);
        // 要使用压缩，必须指定压缩方式为MODE_EXPLICIT 
        imgWriteParams.setCompressionMode(imgWriteParams.MODE_EXPLICIT); 
        // 这里指定压缩的程度，参数qality是取值0~1范围内， 
        imgWriteParams.setCompressionQuality((float)0.5); 
        imgWriteParams.setProgressiveMode(imgWriteParams.MODE_DISABLED); 
        ColorModel colorModel = ColorModel.getRGBdefault(); 
        // 指定压缩时使用的色彩模式 
        imgWriteParams.setDestinationType(new javax.imageio.ImageTypeSpecifier(colorModel, colorModel 
                .createCompatibleSampleModel(16, 16))); 
        BufferedImage image = new BufferedImage(newWidth, newHeight, BufferedImage.TYPE_INT_RGB);
        Graphics2D g2d = image.createGraphics(); 
        image = g2d.getDeviceConfiguration().createCompatibleImage(newWidth,newHeight,Transparency.TRANSLUCENT); 
        g2d.dispose(); 
        g2d = image.createGraphics(); 
        Image from = targetImage.getScaledInstance(newWidth, newHeight, targetImage.SCALE_AREA_AVERAGING); 
        g2d.drawImage(from, 0, 0, null);
        g2d.dispose();
       
        System.out.println("原图片大小=================="+file.length());
        System.out.println("原图片路径=================="+file.getCanonicalPath());

        FileOutputStream out = new FileOutputStream(file); 
        imgWrier.reset(); 
        // 必须先指定 out值，才能调用write方法, ImageOutputStream可以通过任何 OutputStream构造 
        imgWrier.setOutput(ImageIO.createImageOutputStream(out)); 
        // 调用write方法，就可以向输入流写图片 
        imgWrier.write(null, new IIOImage(image, null, null), imgWriteParams); 
        out.flush(); 
        out.close(); 
        System.out.println("新图片大小=================="+file.length());
        return file;
    }


大小改变，质量不变
public static File resize20180224(Float quality, File file, Image targetImage) throws ImageFormatException, IOException {
    int targetWidth = targetImage.getWidth(null);
        int targetHeight = targetImage.getHeight(null);
    int width = Math.max(targetWidth, 1);
        int height = Math.max(targetHeight, 1);
        double rate=2.0;
       /* if(file.length()>=1024000){
        rate= file.length()/(double)1024000;
        }*/
        int newWidth = (int) (((double) width) / rate);
        int newHeight = (int) (((double) height) / rate);
        BufferedImage image = new BufferedImage(newWidth, newHeight, BufferedImage.TYPE_INT_RGB);
        Graphics2D g2d = image.createGraphics(); 
        image = g2d.getDeviceConfiguration().createCompatibleImage(newWidth,newHeight,Transparency.TRANSLUCENT); 
        g2d.dispose(); 
        g2d = image.createGraphics(); 
        Image from = targetImage.getScaledInstance(newWidth, newHeight, targetImage.SCALE_AREA_AVERAGING); 
        g2d.drawImage(from, 0, 0, null);
        g2d.dispose(); 
       
        /** 设置图片压缩比例 */ 
        if (quality == null || quality <= 0) {
            if(file.length()<2049000){  
            //0.5倍压缩
            quality = (Float)0.5f;//小于2MB
            }else{
            //0.25倍压缩
            quality = (Float)0.25f;//大于2MB
            }
        }
        System.out.println("原图片大小=================="+file.length());
        ImageIO.write(image, "png", file);
        System.out.println("新图片大小=================="+file.length());
        return file;
    }