如何在Java中减小多部分文件的大小

Question

我有一个基于Java Spring MVC的应用程序，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
}

我现在正在尝试通过以下方式减小图像的大小： 增加Java中图像的分辨率并减小大小和在Java中降低图像分辨率 我面临的问题是，在上述示例中，我们处理的是保存到指定位置的java.io.File对象。我不想保存这个图像。是否有任何方法可以使用类似的方式压缩我的多部分图像文件并继续上传。

- Geo Thomas

Answer 1

这是我第一次深入研究ImageIO包。我发现MemoryCacheImageOutputStream可以让你将图像输出流写入输出流，即ByteArrayOutputStream。从那里，数据可以使用toByteArray()和toString()进行检索，经过压缩后。由于我将图像存储到postgresql并将图像存储为字节数组，所以我使用了toByteArray。虽然有些晚了，但我希望它能帮助到某些人。

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();
}

- gov

Answer 2

为什么不在客户端上传之前调整大小呢？这样可以节省一些带宽。

BlueImp JQuery Upload 可以实现此功能。

- Neil McGuigan