In a servlet I had to read an image file from disk, encode it to Base64 and then send back to the client. Because I only found samples for iOS, Python and some other kinds (principally all do it the same way) I thought I post my code here to help others ;)
CAUTION! This should only work for files up to 2GB: setting capacity of ByteBuffer only takes an int.
Why so complicated and why read the complete image into memory? A much simpler solution:
protected void service(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException { sun.misc.BASE64Encoder enc = new sun.misc.BASE64Encoder(); enc.encode(new FileInputStream("/path/to/file.whatever"), response.getOutputStream()); } 
protected void service(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException { FileInputStream in = null; try { File file = new File(getServletContext().getRealPath("/<thePath>/<fileName>")); ByteBuffer buff = ByteBuffer.wrap(new byte[(int)image.length() + (image.length() % 1024 > 0 ? 1024 : 0)]); byte[] b = new byte[1024]; in = new FileInputStream(file); while(in.read(b) != -1) { buff.put(b); } response.getWriter().write(Base64.encode(buff.array())); } catch(Exception e) { String msg = "Fehler beim lesen des Bildes"; LOG.log(Level.SEVERE, msg, e); response.sendError(500, msg); return; } finally { if(in != null) in.close(); } } CAUTION! This should only work for files up to 2GB: setting capacity of ByteBuffer only takes an int.
org.apache.commons.codec.binary.Base64InputStreamString (code is just a snippet) and pack it with some other data before sending the response, so I don't see actually an additional value for me, just that I got an additional lib. But I think I will use it future projects.Base64InputStream in another way like I did. And if its just about not loading data in memory I find Udo Klimaschewskis answer cleaner and it don't need an additional library.Base64InputStream stream = new Base64InputStream(new FileInputStream("path to file")); IOUtils.copy(stream, response.getOutputStream());`