ImageIO.createImageInputStream保持返回null [英] ImageIO.createImageInputStream Keeps Returning null

问题描述

嘿所有，
每当我尝试使用 ImageIO.createImageInputStream 获取 ImageInputStream 对象时返回 null ，没有异常，警告或错误。我尝试将不同的数据类型传递给函数，一个简单的文件和一个 InputStream ，但都返回 null 也。文档说如果找不到合适的 ImageInputStreamSpi 那么该函数将返回 null ，但该文件是一个bog-标准的JPEG，当然Java带有一个开箱即用的这种格式的服务提供商？
感谢您的时间。

Hey all, Whenever I try to get an ImageInputStream object using ImageIO.createImageInputStream it simply returns null with no exceptions, warnings or errors. I have tried passing different data types to the function, a simple File, and an InputStream, but both returned null also. The documentation says that if no suitable ImageInputStreamSpi is found then the function will return null, but the file is a bog-standard JPEG, and surely Java comes with a service provider for such a format out of the box? Thanks for your time.

/**
 * Reads in an image from a file and returns the image in a
 * {@code BufferedImage} object.
 *
 * @param source the file to create the {@code BufferedImage}
 * from.
 * @return the {@code BufferedImage} object representing the image
 * in {@code source}.
 */
private BufferedImage readImage( File source ) {
    // There is only one image in this file
    final int imageIndex = 0;
    BufferedImage image = null;

    try {
        // Get the ImageReader object for this filetype
        Iterator readers =
            ImageIO.getImageReaders( source );
        ImageReader reader = (ImageReader) readers.next();

        // Create an ImageInputStream object from the source image file
        ImageInputStream iis = ImageIO.createImageInputStream( source );
        // Raises IllegalArgumentException, because iis is null
        reader.setInput( iis, true );

        // Read the image file
        image = reader.read( imageIndex );
    } catch ( Exception exception ) {
        exception.printStackTrace();
        System.exit( -1 );
    }

    return image;
}

推荐答案

你为什么这么做??
你可以简单地这样做：

Why are you doing all that?? you can simply do this:

image = ImageIO.read(source);

否迭代器， ImageInputStreams ......一无所获！

No Iterators, ImageInputStreams... no nothing !

编辑：既然你坚持认为，你的代码不能正常工作，因为你'发送文件到 ImageIO.getImageReaders（）而不是 ImageInputStream 。所以你的代码看起来应该是这样的：

EDIT: Since you insist, your code is not working because you're sending a File to ImageIO.getImageReaders() instead of a ImageInputStream. SO your code should look something like that:

ImageInputStream iis = ImageIO.createImageInputStream(source);
Iterator readers = ImageIO.getImageReaders(iis);
ImageReader reader = (ImageReader) readers.next();

reader.setInput(iis, false);
image = reader.read(imageIndex);

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