ImageIO 中的异常 "java.lang.IllegalArgumentException: image == null!"

Question

我正在尝试从字节数组写入 png 文件。

我的应用程序抛出以下异常 "java.lang.IllegalArgumentException: image == null!" in ImageIO

我使用随机字节数组测试了我的解决方案，如下面的代码片段所示，但仍然抛出异常。

你能帮我确定为什么会被抛出吗？

    import java.io.ByteArrayOutputStream;
    import java.io.File;
    import java.io.IOException;
    import java.util.Random;
    import javax.imageio.ImageIO;
    public class Main {

        public static void main(String[] args) throws IOException {
            String fn = new String("C:\Users\frogwine\Desktop\P1.png");

            byte [] data = new byte[256];

            Random r = new Random();
            r.nextBytes(data);
            ByteArrayInputStream bis = new ByteArrayInputStream(data);
            ByteArrayInputStream input_stream= new ByteArrayInputStream(data);
            BufferedImage final_buffered_image = ImageIO.read(input_stream);
            ImageIO.write(final_buffered_image , "png", new File(fn) );
        }


    }

堆栈跟踪：

    "C:\Program Files\Java\jdk-13.0.1\bin\java.exe" "-javaagent:C:\Program Files\JetBrains\IntelliJ IDEA Community Edition 2019.3\lib\idea_rt.jar=57315:C:\Program Files\JetBrains\IntelliJ IDEA Community Edition 2019.3\bin" -Dfile.encoding=UTF-8 -classpath C:\Users\frogwine\Documents\deneme\out\production\deneme com.berk.Main
    Exception in thread "main" java.lang.IllegalArgumentException: image == null!
        at java.desktop/javax.imageio.ImageTypeSpecifier.createFromRenderedImage(ImageTypeSpecifier.java:925)
        at java.desktop/javax.imageio.ImageIO.getWriter(ImageIO.java:1608)
        at java.desktop/javax.imageio.ImageIO.write(ImageIO.java:1540)
        at com.berk.Main.main(Main.java:23)

    Process finished with exit code 1

Answer 1

嗯，这并不奇怪。来自 ImageIO.read 文档：

If no registered ImageReader claims to be able to read the resulting stream, null is returned.

将随机字节写入数组不会创建任何格式的有效图像数据，因为图像格式具有至少由 header 组成的标准结构。为此，ImageIO.read returns null.

Answer 2

正如 Leo 还提到的，只是将随机字节传递给 ImageIO.read 方法，您无法获得随机图像。您将获得空图像，当您将其传递给 write 方法时，它将抛出此 IllegalArgumentException。

相反，您可以创建具有预定义宽度和高度的空图像并设置 RGB 颜色值以获得如下随机图像。

import javax.imageio.ImageIO;
import java.awt.image.BufferedImage;
import java.io.File;
import java.io.IOException;
import java.security.NoSuchAlgorithmException;
import java.security.SecureRandom;
public class Main {

    public static void main(String[] args) throws IOException {
        String fn = new String("C:\Users\frogwine\Desktop\P1.png");
        ImageIO.write(generateRandomImage(300) , "png", new File(fn) );
    }


    public static BufferedImage generateRandomImage(int numOfPixels) {
        final double ASPECT_RATIO = 4.0 / 3.0;
        int width = 0;
        int height = 0;
        byte[] rgbValue = new byte[3];
        BufferedImage image = null;
        SecureRandom random = null;

        try {
            random = SecureRandom.getInstance("SHA1PRNG");

            width = (int) Math.ceil(Math.sqrt(numOfPixels * ASPECT_RATIO));
            height = (int) Math.ceil(numOfPixels / (double) width);

            image = new BufferedImage(width, height, BufferedImage.TYPE_INT_RGB);
            for (int x = 0; x < width; x++) {
                for (int y = 0; y < height; y++) {
                    random.nextBytes(rgbValue);
                    image.setRGB(x, y,
                            byteToInt(rgbValue[0]) + (byteToInt(rgbValue[1]) << 8) + (byteToInt(rgbValue[2]) << 16));
                }
            }

            return image;
        } catch (NoSuchAlgorithmException nsaEx) {
            nsaEx.printStackTrace();
        }
        return null;
    }

    public static int byteToInt(int b) {
        int i = b;
        if (i < 0) {
            i = i + 256;
        }
        return i;
    }

ImageIO 中的异常 "java.lang.IllegalArgumentException: image == null!"

Exception "java.lang.IllegalArgumentException: image == null!" in ImageIO

java

javax.imageio