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Module 4: Backend — Experiments Hub, Theory & Calculator Business Logic

Team Role: Jayesh Sharma — Member 4 (Backend Developer 2)
Layer: Controller & Business Logic Layer (MVC Architecture)
Technologies: Java EE Servlets, Java Business Logic, Expression Parsing, CSV Streaming (RFC 4180), Request Dispatching

1. Overview & Responsibilities

This module implements the server-side business logic and controllers for the academic core of the portal: the dynamic experiments system, theory publishing workflows, the student feedback pipeline, employee CRUD desk, and mathematical computation engines.

  • Dynamic Experiment Hub Controller:
    • ExperimentServlet.java: Loads the ordered catalog of built-in and teacher-added experiments from ExperimentDAO. Processes teacher submissions for new experiments and persists them.
  • Employee Registration Desk CRUD Controller (Experiment 5):
    • EmployeeServlet.java: Controller for Experiment 5. Processes CRUD requests (save, search, update, delete, clean). Validates employee IDs and contact numbers, delegates persistence to EmployeeDAO.java, and sets structured status messages and model attributes for exp5.jsp.
  • Role-Based Feedback Pipeline & Data Streaming:
    • FeedbackServlet.java: Overhauled controller managing Experiment 10.
      • Action exp10_login: Authenticates users and registers session with ActiveSessionManager.
      • Action exp10_register: Dispatches student self-registration.
      • Action exp10_logout: Terminates session and cleans up active device registry.
      • Action submit: Accepts student feedback (subject, faculty name, rating, text), validates constraints, persists via FeedbackDAO, and redirects student to confirmation view without exposing peer records.
      • Action list: Teacher-only action retrieving filtered feedback records based on faculty, course, and rating.
      • Action exportCsv: Direct server-side streaming of RFC 4180 compliant CSV reports with Content-Disposition: attachment; filename=feedback_report.csv and MIME type text/csv for instant Excel analysis.
  • Theory & Study Content Controller:
    • TheoryServlet.java: Handles retrieval of published theory notes for all users, as well as teacher-only note publishing and deletion actions through TheoryContentDAO.
  • MVC Architecture Implementation (Experiment 3):
    • CalculatorModel.java: Core business model that parses mathematical expressions, handles operator precedence, validates input strings, and computes results.
    • CalculatorServlet.java: Controller that accepts calculation requests from exp3.jsp, delegates computation to CalculatorModel, attaches result models to the request scope, and forwards to the view.
  • Arithmetic Processing (Experiment 8):
    • ArithmeticServlet.java: Backend servlet handling arithmetic calculations (+, -, *, /) with defensive numeric parsing and division-by-zero checks.

2. Files Handled

File Path Description
src/main/java/com/javalab/servlet/ExperimentServlet.java Controller managing lab experiment listings and custom experiment registration
src/main/java/com/javalab/servlet/EmployeeServlet.java Controller handling Employee CRUD operations (save, search, update, delete, clean)
src/main/java/com/javalab/servlet/FeedbackServlet.java Controller handling role-based feedback actions, student submission, and CSV streaming
src/main/java/com/javalab/servlet/TheoryServlet.java Controller managing retrieval, publishing, and removal of theory content
src/main/java/com/javalab/servlet/CalculatorServlet.java MVC Controller routing calculations between JSP view and Calculator model
src/main/java/com/javalab/servlet/ArithmeticServlet.java Controller processing arithmetic operations with defensive division-by-zero validation
src/main/java/com/javalab/calc/CalculatorModel.java Pure Java business logic model performing mathematical expression evaluation

3. Cross-Module Integration Contracts

  • Integration with Member 1 & 2 (Frontend Views):
    • Consumes requests from exp3.jsp, exp5.jsp, arithmetic.jsp, theoryList.jsp, feedback.jsp, and feedbackList.jsp, forwarding computed attributes back to the view layer.
  • Integration with Member 5 (Database Persistence):
    • Persists and queries lab data via ExperimentDAO.java, EmployeeDAO.java, TheoryContentDAO.java, and FeedbackDAO.java.

4. Technical Architecture & Engineering Highlights

  • Streamed Binary / Text Exporting:
    • Implemented direct servlet-to-browser CSV streaming using proper RFC 4180 escaping and HTTP headers, enabling high-performance export without server memory bloat.
  • Complete Employee CRUD Controller:
    • Standardized CRUD lifecycle operations with transactional validation, parameterized queries, and clean view dispatching.
  • Strict MVC Decoupling & Component Lifecycle:
    • Separated user interface templates (exp3.jsp), request routing (CalculatorServlet.java), and computational algorithms (CalculatorModel.java), demonstrating classic 3-tier MVC architecture.