Best way for transfering files via socket in java

Question

I have a BufferedReader object and a PrintWriter object. So I can work passing String objects made by json-io of any type (e.g.: List, Map, MyOwnClass)

My class have a byte[] attribute, this byte[] will keep a file bytes, such as an image.

The json generated of my class is very very big, obviously... Then i started to think that must have a better way to transfer files.

Should I change all the mechanism to transfer only byte[] instead of String? Does someone know what is the mechanism used by chat programs? Should I reserve the first 20 bytes of the array for the message identification?

Answer 1

I would write it to the socket in binary:

Assuming a class with one String and one byte[].

1. The String
   • The length of the String is written with DataOutputStream.writeInt(int) (or methods for smaller integers) and then OutputStream.write(byte[]) on the return value of String.getBytes(String) with the charset explicitly specified.
2. The byte[]
   • The length is written with DataOutputStream.writeInt(int) (or methods for smaller integers) and then OutputStream.write(byte[]) for the byte[] to transfer.

On the other side you would do the exact opposite of this procedure.

I chose this binary approach over JSON because even though you could transmit the byte[] with JSON almost as efficiently as in binary, it would defeat the very purpose of JSON: being human-readable.