Question

我有Java Spring MVC个应用程序，其中有一个选项可以上传图像并保存到服务器。我有以下方法：

@RequestMapping(value = "/uploaddocimagecontentsubmit", method = RequestMethod.POST)
public String createUpdateFileImageContentSubmit(@RequestParam("file") MultipartFile file, ModelMap model)
{
//methods to handle file upload
}

我现在正在尝试减小图像的大小，参考以下内容：

increasing-resolution-and-reducing-size-of-an-image-in-java和decrease-image-resolution-in-java 我面临的问题是，在上面的例子中，我们正在处理保存到指定位置的java.io.File个对象。我不想保存图像。有什么方法可以使用类似的东西来压缩我的Multipart Image文件并继续上传。

Answer 1

这是我第一次深入研究 ImageIO 包。我遇到了 MemoryCacheImageOutputStream，它允许您将图像输出流写入输出流，即 ByteArrayOutputStream。从那里，可以在压缩后使用 toByteArray() 和 toString() 检索数据。我使用 toByteArray，因为我将图像存储到 postgresql 并将图像存储为字节数组。我知道这已经晚了，但我希望它可以帮助某人。

private byte[] compressImage(MultipartFile mpFile) {
    float quality = 0.3f;
    String imageName = mpFile.getOriginalFilename();
    String imageExtension = imageName.substring(imageName.lastIndexOf(".") + 1);
    // Returns an Iterator containing all currently registered ImageWriters that claim to be able to encode the named format.
    // You don't have to register one yourself; some are provided.
    ImageWriter imageWriter = ImageIO.getImageWritersByFormatName(imageExtension).next();
    ImageWriteParam imageWriteParam = imageWriter.getDefaultWriteParam();
    imageWriteParam.setCompressionMode(ImageWriteParam.MODE_EXPLICIT); // Check the api value that suites your needs.
    // A compression quality setting of 0.0 is most generically interpreted as "high compression is important,"
    // while a setting of 1.0 is most generically interpreted as "high image quality is important."
    imageWriteParam.setCompressionQuality(quality);
    ByteArrayOutputStream baos = new ByteArrayOutputStream();
    // MemoryCacheImageOutputStream: An implementation of ImageOutputStream that writes its output to a regular
    // OutputStream, i.e. the ByteArrayOutputStream.
    ImageOutputStream imageOutputStream = new MemoryCacheImageOutputStream(baos);
    // Sets the destination to the given ImageOutputStream or other Object.
    imageWriter.setOutput(imageOutputStream);
    BufferedImage originalImage = null;
    try (InputStream inputStream = mpFile.getInputStream()) {
        originalImage = ImageIO.read(inputStream); 
    } catch (IOException e) {
        String info = String.format("compressImage - bufferedImage (file %s)- IOException - message: %s ", imageName, e.getMessage());
        logger.error(info);
        return baos.toByteArray();
    }
    IIOImage image = new IIOImage(originalImage, null, null);
    try {
        imageWriter.write(null, image, imageWriteParam);
    } catch (IOException e) {
        String info = String.format("compressImage - imageWriter (file %s)- IOException - message: %s ", imageName, e.getMessage());
        logger.error(info);
    } finally {
        imageWriter.dispose();
    }
    return baos.toByteArray();
}

Answer 2

为什么不在上传前在客户端调整大小？这将节省一些带宽

BlueImp JQuery Upload可以做到这一点

如何减少java中多部分文件的大小

2 个答案: