JPEG ImageReader's getRawImageType() method is expected to return a type specifier which closely represents the internal format of the image. Currently it returns 'null'. The documentation claims that the return value must be included in the list of values returned by getImageTypes() and nowhere specifies that an implementation may choose to return a null value. For PNG and GIF, this method returns the first value of getImageTypes() which is as per the specification. If returning null is an expected behaviour for JPEG then it must be documented accordingly.

I have attached a sample code which would show the list of type specifiers returned by getImageTypes() and getRawImageType() for a JPEG Image.

This is seen on Solaris as well as Windows right from JDK1.4+.