在JRuby（Java）中将BufferedImage编码为Base64

Question

I'm dynamically creating a BufferedImage and trying to encode it to Base64 string so that I can display an image in template like so:

<img src="data:image/gif;base64, [base 65 string]>

I have a BufferedImage variable which I tried to write to disk for test and the image gets written successfully:

ImageIO.write(@img, "gif", Java::JavaIo::File.new(filename))

How can I obtain bytes string from the @img variable (without writing to disk) so that I can encode it into Base64 and display it in my template?

Answer 1

You can wrap a StringIO in a org.jruby.util.IOOutputStream with the to_outputstream method and write to that, then get the bytes with StringIO#string :

sio = StringIO.new
outputstream = sio.to_outputstream

ImageIO.write(@img, "gif", outputstream)

encoded = Base64.encode64(sio.string)