Question

How to call setInput of ImageReader class?
Below is my code:

ImageInputStream iis = ImageIO.createImageInputStream(newByteArrayInputStream(cipherData));    
Iterator<ImageReader> readers=ImageIO.getImageReaders(iis);
Iterator<ImageReader> readers=ImageIO.getImageReaders(iis);
System.out.println("readers="+readers);

Answer 1

If you mean calling the method on the ImageReaders contained in your readers variable, you could loop over them:

for (Iterator<ImageReader> it=ImageIO.getImageReaders(iis); it.hasNext();) {
    ImageReader reader = it.next();
    readers.setInput(someObject);
}

EDIT

If you only want the first element:

Iterator<ImageReader> it=ImageIO.getImageReaders(iis);
ImageReader reader = null;
if (it.hasNext()) {
    reader = it.next();
}
//you probably want to check for null here to make sure there was one element