Java BufferedImage JPG压缩而无需写入文件 [英] Java BufferedImage JPG compression without writing to file

问题描述

我已经看到使用Java BufferedImage 制作压缩JPG图像的几个例子。 c $ c>通过写入文件来实现对象，但是可以在不写入文件的情况下执行JPG压缩吗？也许是通过像 this 这样的 ByteArrayOutputStream 来写的？

I've seen several examples of making compressed JPG images from Java BufferedImage objects by writing to file, but is it possible to perform JPG compression without writing to file? Perhaps by writing to a ByteArrayOutputStream like this?

ImageWriter jpgWriter = ImageIO.getImageWritersByFormatName("jpg").next();
ImageWriteParam jpgWriteParam = jpgWriter.getDefaultWriteParam();
jpgWriteParam.setCompressionMode(ImageWriteParam.MODE_EXPLICIT);
jpgWriteParam.setCompressionQuality(0.7f);

ImageOutputStream outputStream = createOutputStream();
jpgWriter.setOutput(outputStream);
IIOImage outputImage = new IIOImage(image, null, null);

// in this example, the JPG is written to file...
// jpgWriter.write(null, outputImage, jpgWriteParam);
// jpgWriter.dispose();

// ...but I want to compress without saving, such as
ByteArrayOutputStream compressed = ???

推荐答案

只需传递您的 ByteArrayOutputStream 到 ImageIO.createImageOutputStream（...）像这样：

Just pass your ByteArrayOutputStream to ImageIO.createImageOutputStream(...) like this:

// The important part: Create in-memory stream
ByteArrayOutputStream compressed = new ByteArrayOutputStream();
ImageOutputStream outputStream = ImageIO.createImageOutputStream(compressed);

// NOTE: The rest of the code is just a cleaned up version of your code

// Obtain writer for JPEG format
ImageWriter jpgWriter = ImageIO.getImageWritersByFormatName("jpg").next();

// Configure JPEG compression: 70% quality
ImageWriteParam jpgWriteParam = jpgWriter.getDefaultWriteParam();
jpgWriteParam.setCompressionMode(ImageWriteParam.MODE_EXPLICIT);
jpgWriteParam.setCompressionQuality(0.7f);

// Set your in-memory stream as the output
jpgWriter.setOutput(outputStream);

// Write image as JPEG w/configured settings to the in-memory stream
// (the IIOImage is just an aggregator object, allowing you to associate
// thumbnails and metadata to the image, it "does" nothing)
jpgWriter.write(null, new IIOImage(image, null, null), jpgWriteParam);

// Dispose the writer to free resources
jpgWriter.dispose();

// Get data for further processing...
byte[] jpegData = compressed.toByteArray();

PS：默认情况下，将使用 ImageIO 创建 ImageOutputStream 时进行磁盘缓存。这可能会减慢内存中流的写入速度。要禁用它，请使用 ImageIO.setCache（false）（全局禁用磁盘缓存）或显式创建 MemoryCacheImageOutputStream （本地），就像这样：

PS: By default, ImageIO will use disk caching when creating your ImageOutputStream. This may slow down your in-memory stream writing. To disable it, use ImageIO.setCache(false) (disables disk caching globally) or explicitly create an MemoryCacheImageOutputStream (local), like this:

ImageOutputStream outputStream = new MemoryCacheImageOutputStream(compressed);

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