How do I read exactly 4 bytes from an InputStream?

Question

I'm sending JPEGs as byte arrays over a Socket, the 4 first bytes is the length of the JPEG. I have to read these in order to figure out how many bytes i should read to get the actual image. I can't seem to figure out how to do this.

Just reading like this is not guaranteed to give me my 4 bytes:

byte[] JPEGlength = new byte[4];
inputStream.read(lengthBuffer);

I have been thinking over this a lot and I cant seem to figure out how to do this. Help would be very appreciated!

Answer 1

Use DataInputStream.readFully(), but in this case what you really need is DataInputStream.readInt().