manipulate value

Yes I'm a newbie.. I have a parameter:
String docID = request.getHeader("docID");
This will be a 3 or 4 digit number.
Ithen want to take this number and :
1. reverse it (1234 becomes 4321)
2. get a random number between 1- 2
3. Add it to reversed number (4323)
4. multiple by 2 (8646)
5. get another random digits based on first random number (if first number was a 1 then I need one more random number, if the first random number was a 2 then I need two random numbers) for example if the first random number was a 2 then any value between 10 - 99 would be fine if the first random number was a 1 then any value between 0-9 would be acceptable.
6. Append first random number to front of existing number
7. append second random number(s) to end of existing number.

Examples:docID = 321
1. 123
2. random number 2
3. 1232
4. 2464
5. second random number 69 (2 digits because first random number was a 2)  
6.22464
7.2246469