How can I check the correctness of a servlet class?

Question

I'm working on a system which allows students to submit their servlet class to the web. Once they submit their class, the system will input some test case parameters to test the stduen's class is correct or not.
For example, the student servlet class can work out this:
ParameterA + ParameterB = Answer
where "ParameterA", "ParameterB" is the input variables/test case
and "Answer" is the output variable.
That's my question, how can the system know the "Answer" variable is correct or not. I mean the system aims to check the program of the student is correct or not.
What I want the system to do is
Run student servlet program:
2+3=5, then check the answer "5" with the test case answer of the system- "5". In this case, the system marks the student's program as
" CORRECT"
2. 2+3 =7, then check the answer "7" with the test case answer of the system- "5". In this case, the system marks the student's program as
" WRONG"
SO, ANY METHOD THAT CAN ALLOW THE SYSTEM TO "RECOGNIZE" THE STUDENT'S PROGRAM OUTPUT? Becasue the output is expressed in HTML format.
Can anybody kindly give solutions/ideas to me?
THANKS~~~~~~

Answer 1

Then why not use the print writer?
  response.getWriter();Then the student should output their HTML response with the result tagged, for example:
[ANSWER]my answer here[ANSWER]
The square brackets will not be interpreted by the browser, so the student can visually see their results and then all you need to do is write a primative parser on your side:
  String r = blahblah.getResponse();
  int s = r.indexOf("[ANSWER]"), e = r.indexOf("[/ANSWER]");
  String answer = r.subString(s+8,e);  // the 8 is the length of: [ANSWER]Something like that should work...
HTH