Java 将JPEG编码器/解码器支持添加到已安装的OpenJDK

我正在尝试缩放JPEG图像并使用以下代码将其保存回去，但是，生成的

storage/test/thumbnail.jpg

文件只是一个空文件。我用

PNG

格式检查了相同的代码，它工作得非常好。然而，对于我的用例，我需要一个JPG图像，而不是PNG

import java.awt.geom.AffineTransform
import java.awt.image.AffineTransformOp
import java.awt.image.BufferedImage
import java.io.File
import javax.imageio.ImageIO

fun main() {
    val file = File("storage/test/original.jpg")
    val image = ImageIO.read(file.inputStream())
    val thumbnail = thumbnailOf(image)
    val thumbnailFile = File("storage/test/thumbnail.jpg")
    thumbnailFile.parentFile.mkdirs()
    thumbnailFile.outputStream().use { output ->
        ImageIO.write(thumbnail, "JPEG", output)
    }
}

fun thumbnailOf(image: BufferedImage): BufferedImage {
    val width = image.width
    val height = image.height
    val ratio = width / height.toDouble()

    if (ratio == 0.0) {
        error("Cannot determine ratio for ($width*$height)")
    }

    val newWidth = 600
    val newHeight = (newWidth / ratio).toInt()
    val scaledImage = BufferedImage(newWidth, newHeight, BufferedImage.TYPE_INT_ARGB)
    val at = AffineTransform()
    at.scale(newWidth / width.toDouble(), newHeight / height.toDouble())
    val ato = AffineTransformOp(at, AffineTransformOp.TYPE_BICUBIC)

    return ato.filter(image, scaledImage)
}

到目前为止，我能找到的最好的答案是这个答案，它表明OpenJDK没有JPEG编码器。那么，如果是这样的话，如何将JPEG编码器（或解码器）添加到当前安装的OpenJDK中

我当前安装的OpenJDK

openjdk version "12" 2019-03-19
OpenJDK Runtime Environment (build 12+33)
OpenJDK 64-Bit Server VM (build 12+33, mixed mode, sharing)

---

好的，下面是我如何解决这个问题的

就我而言，这个问题与JPEG支持无关。JPEG已经被支持了，但是，我的代码中有一些错误。此外，我使用了不同的方法来缩放图像

第一个bug出现在这一行：

ImageIO.write

找不到与

BuffereImage.TYPE_INT\u ARGB

和

JPG

/

JPEG

匹配的

ImageWriter

。因此，我将其更改为

BufferedImage.TYPE\u INT\u RGB

修复此问题将导致在

ato.filter（图像、缩放图像）

我不知道这个异常的原因是什么以及如何修复它，但是使用

Graphics2D

对象来缩放和渲染图像对我来说很有用

即使生成了有效的图像文件，但它只包含黑色背景。这是因为提供的

scale（）

的值不一致

下面是最后一段代码，它成功地工作了，以及第2点和第3点是如何修复的

import java.awt.Graphics2D
import java.awt.image.BufferedImage
import java.io.File
import javax.imageio.ImageIO

fun main() {
    val file = File("storage/test/original.jpg")
    val image = ImageIO.read(file.inputStream())
    val thumbnail = thumbnailOf(image)
    val thumbnailFile = File("storage/test/thumbnail.jpg")
    thumbnailFile.parentFile.mkdirs()
    thumbnailFile.outputStream().use { output ->
        ImageIO.write(thumbnail, "JPEG", output)
    }
}

fun thumbnailOf(image: BufferedImage): BufferedImage {
    val width = image.width
    val height = image.height
    val ratio = width / height.toDouble()

    if (ratio == 0.0) {
        error("Cannot determine ratio for ($width*$height)")
    }

    val newWidth = 600
    val newHeight = (newWidth / ratio).toInt()
    val scale = newWidth / width.toDouble()

    val scaledImage = BufferedImage(newWidth, newHeight, BufferedImage.TYPE_INT_RGB)

    val graph = scaledImage.graphics as Graphics2D
    // graph.scale((newWidth / width).toDouble(), (newHeight / height).toDouble())
    graph.scale(scale, scale)

    // everything drawn with graph from now on will get scaled.
    graph.drawImage(image, 0, 0, null)
    graph.dispose()

    return scaledImage
}

Exception in thread "main" java.awt.image.ImagingOpException: Unable to transform src image

import java.awt.Graphics2D
import java.awt.image.BufferedImage
import java.io.File
import javax.imageio.ImageIO

fun main() {
    val file = File("storage/test/original.jpg")
    val image = ImageIO.read(file.inputStream())
    val thumbnail = thumbnailOf(image)
    val thumbnailFile = File("storage/test/thumbnail.jpg")
    thumbnailFile.parentFile.mkdirs()
    thumbnailFile.outputStream().use { output ->
        ImageIO.write(thumbnail, "JPEG", output)
    }
}

fun thumbnailOf(image: BufferedImage): BufferedImage {
    val width = image.width
    val height = image.height
    val ratio = width / height.toDouble()

    if (ratio == 0.0) {
        error("Cannot determine ratio for ($width*$height)")
    }

    val newWidth = 600
    val newHeight = (newWidth / ratio).toInt()
    val scale = newWidth / width.toDouble()

    val scaledImage = BufferedImage(newWidth, newHeight, BufferedImage.TYPE_INT_RGB)

    val graph = scaledImage.graphics as Graphics2D
    // graph.scale((newWidth / width).toDouble(), (newHeight / height).toDouble())
    graph.scale(scale, scale)

    // everything drawn with graph from now on will get scaled.
    graph.drawImage(image, 0, 0, null)
    graph.dispose()

    return scaledImage
}