Java™ Media APIs: Cross-Platform Imaging, Media, and Visualization

Service Provider Interfaces

One obvious question resulting from the previous discussion is how do the ImageIO static methods know which ImageReader(s) can decode the image data? Theoretically, one way this can be done is to have each of the ImageReaders contain a set of methods that would return a list of image formats, file suffixes, and MIME types that it can decode. Another method could take an ImageInputStream and return true or false if the ImageReader can decode it. Using these techniques, it would be up to the plug-in developers to write these methods and therefore provide this information. Although this idea has its merits, there is one problem: In order to find out an ImageReader's functionality, it needs to be registered; and to register ...