Java obtain image, check mime type, convert to png and return that image

I'm trying 开发者_如何学运维to build a java servlet to obtain an image from an URL, check it's mime type and convert it if necessary, and then return that image. What objects should I use, can you provide me some examples specially for obtaining the image and returning it?

Thanks a lot

Just use JAI (intro reference):

URL url = "// URL of the remote image to be read //";
RenderedImage original = JAI.create("url", url);
JAI.create("encode", original, response.getOutputStream(), "png");

Where response is an HttpServletResponse. Note that checking the mime-type isn't needed, JAI will do what's necessary to figure out how to read the image under the covers.