如何将图像从Java应用程序发送到Android应用程序？

Question

I have a client-server application. The server is pure Java, the client is an Android application. They communicate over TCP using a ServerSocket.

I want to create an Image on the server, edit it (eg draw lines on it) and then send it to the client to display it there as a Bitmap on the screen.

My first approach was to import the android.graphics.Bitmap library into the server to use it there, but of course since you can't use Android libraries outside of an Android environment this can't work.

My approach now is to use a BufferedImage on the server, but the problem is that I couldn't find out how to serialize this in a way that the client can then reconstruct a Bitmap out of it. I tried using ImageIO.write, but then what do I have to do on the client-side?

Does anyone have an idea on how to solve this, or has a better approach? I appreciate your help.

Answer 1

Any PNG or JPG image can be decoded in Android using the BitmapFactory class. Get an InputStream for the image then use BitmapFactory.decodeStream(inputStream) . It doesn't need to be serialized specially...just send the bytes for the image.

Answer 2

There are two ways to get raw stream of bytes on your client Android application.

1. Using getPixels function
2. Using copyPixelsToBuffer function

getPixels is straightforward and gives you basic raw bytes. copyPixelsToBuffer copies in a buffer.

Once you have the raw bytes, send them to your server. Here, on the server side Java, you can use a library such as ImageJ to convert back your raw byte stream into Image, process it, convert it back and send back to Android.

When your client application receives back the raw_stream, convert it again into android.graphics.Bitmap by using the setPixels or copyPixelsFromBuffer function.