2.Java 图片质量压缩与图片缩放

Java 图片压缩：像素质量压缩 、图片长宽缩放。常用方式：一种为Java有BufferedImage来处理；另一种为谷歌的Thumbnailator处理。如果为文件流处理图片的时候，推荐使用第一种；如果

路径读取文件，推荐选择第二种。

1.BufferedImage来处理

    1.1 质量压缩

//读取图片文件流
BufferedImage image = ImageIO.read(inputStream);

// 得到指定Format图片的writer
Iterator iter = ImageIO.getImageWritersByFormatName("JPEG");
ImageWriter imageWriter = iter.next();

// 得到指定writer的输出参数设置(ImageWriteParam )
ImageWriteParam iwp = imageWriter.getDefaultWriteParam();
iwp.setCompressionMode(ImageWriteParam.MODE_EXPLICIT); // 设置可否压缩iwp.setCompressionQuality(2000000); // 设置压缩质量参数iwp.setProgressiveMode(ImageWriteParam.MODE_DISABLED);
ColorModel colorModel = ColorModel.getRGBdefault();

// 指定压缩时使用的色彩模式
iwp.setDestinationType(new javax.imageio.ImageTypeSpecifier(colorModel,
colorModel.createCompatibleSampleModel(16, 16)));

// 开始打包图片，写入byte[]
ByteArrayOutputStream byteArrayOutputStream =new ByteArrayOutputStream(); // 取得内存输出流
IIOImage iIamge =new IIOImage(image, null, null);

// 此处因为ImageWriter中用来接收write信息的output要求必须是ImageOutput
// 通过ImageIo中的静态方法，得到byteArrayOutputStream的ImageOutput
imageWriter.setOutput(ImageIO.createImageOutputStream(byteArrayOutputStream));
imageWriter.write(null, iIamge, iwp);

InputStream sbs =new ByteArrayInputStream(byteArrayOutputStream.toByteArray());

//输入文件流
ByteArrayOutputStream outStream = new ByteArrayOutputStream();
ImageIO.write(ImageIO.read(sbs), "JPEG", outStream);
return outStream.toByteArray(); 

    1.2 图片长宽缩放

//读取图片文件流
BufferedImage image = ImageIO.read(inputStream);
int width = image.getWidth(); int height = image.getHeight(); 
//判断图片的摆放位置(横向图片 纵向图片)
if(width >4000  || height >4000){
    BigDecimal value;
    //定义的基准为4K
    BigDecimal bignum1 =new BigDecimal("4000");
    //获取相对应的比例
    if(image.getWidth() > image.getHeight()){
        BigDecimal bignum2 =new BigDecimal(image.getWidth());
        value = bignum1.divide(bignum2, 2);
    }else{
        BigDecimal bignum2 =new BigDecimal(image.getHeight());
        value = bignum1.divide(bignum2, 2);
    }

    //缩小相应的比例
     if(value.doubleValue() <1){
        width =new BigDecimal(image.getWidth()).multiply(value).intValue();
        height =new BigDecimal(image.getHeight()).multiply(value).intValue();
        //重绘图片
        BufferedImage imageNew =new BufferedImage(width,                 height,BufferedImage.TYPE_INT_RGB);

        imageNew.getGraphics().drawImage(image, 0, 0, width, height, null); // 绘制缩小后的图

        ByteArrayOutputStream outStream =new ByteArrayOutputStream();         ImageIO.write(imageNew, "JPEG", outStream);
        //把outStream里的数据写入内存
        return outStream.toByteArray();
 }

2.Thumbnailator处理

    2.1 质量压缩 

    Thumbnails.of(path).scale(1f).outputQuality(0.25f).toFile(toPic);
    outputQuality就是用来控制图片质量的

     2.2 图片长宽缩放 

ByteArrayOutputStream out = new ByteArrayOutputStream();
Thumbnails.of(path).size(ppi, ppi).outputFormat("png").toOutputStream(out);
return  out.toByteArray();

备注：读取文件流时，使用thumbnailator 时部分图片抛异常(因此推荐Java BufferedImage)

net.coobird.thumbnailator.tasks.UnsupportedFormatException: No suitable ImageReader foundfor source data.

    at net.coobird.thumbnailator.tasks.io.InputStreamImageSource.read(Unknown Source)

    at net.coobird.thumbnailator.tasks.SourceSinkThumbnailTask.read(Unknown Source)

    at net.coobird.thumbnailator.Thumbnailator.createThumbnail(Unknown Source)

    at net.coobird.thumbnailator.Thumbnails$Builder.toOutputStream(Unknown Source)