使用IOUtils和ImageIO编写图像文件有什么区别

Question

I have a tiff image stored as Base64 encoded String in a file. My aim is to create a tiff file out of it. This is what I am doing:

String base64encodedTiff = IOUtils.toString(new FileInputStream("C:/tiff-attachment.txt"));    
byte[] imgBytes = DatatypeConverter.parseBase64Binary(base64encodedTiff);
BufferedImage bufImg = ImageIO.read(new ByteArrayInputStream(imgBytes));   
ImageIO.write(bufImg, "tiff", new File("c:/new-darksouls-imageIO-tiff.tiff")); 

ImageIO.write() is throwing IllegalArgumentException because bufImg is null. I don't understand what am I doing wrong here.

On the contrary if I use IOUtils to write, it works fine:

IOUtils.write(imgBytes, new FileOutputStream("c:/new-darksouls-io-tiff.tiff"));

Please help me understand

1. Why ImageIO is throwing exception
2. What is the right API and way for what I am trying to achieve.

Answer 1

ImageIO would be useful if, for example, you wanted to convert a PNG to a JPEG. Since you don't need to manipulate the image or convert to another format, don't bother with ImageIO. Just use IOUtils.write() to save the TIFF data verbatim.

ImageIO.read() is returning a null image because it can't read the TIFF file, probably because TIFF isn't one of the standard ImageIO plugin formats. The standard supported image formats are listed here:

http://docs.oracle.com/javase/6/docs/api/javax/imageio/package-summary.html

An additional note -- the code you posted buffers the entire image in memory. If you're concerned about using memory efficiently, consider using some kind of Base64 decoding input stream to perform the decoding on the fly. That might look like this:

try (FileOutputStream out = new FileOutputStream("c:/new-darksouls-io-tiff.tiff");
     FileInputStream in = new FileInputStream("C:/tiff-attachment.txt");
     Base64InputStream decodedIn = new Base64InputStream(in)) {

    IOUtils.copy(decodedIn, out);
}