Electricity Bill Servlet Application

This is a Java Servlet-based web application for managing electricity bills.

Project Structure

ElectricityBillServlet
├── style.css                           (existing)
├── index.html                          (existing)
├── DATABASE_SETUP.sql                  (SQL database setup)
├── src/
│   ├── DBConnection.java               (Database connection manager)
│   ├── HtmlUtil.java                   (HTML generation utilities)
│   ├── HomeServlet.java                (Home/redirect page)
│   ├── LoginServlet.java               (Login handler)
│   ├── RegisterServlet.java            (Registration handler)
│   ├── DashboardServlet.java           (Dashboard display)
│   ├── CalculateBillServlet.java       (Bill calculation)
│   ├── HistoryServlet.java             (Bill history display)
│   └── LogoutServlet.java              (Logout handler)
│
└── WEB-INF/
    ├── web.xml                         (Servlet configuration)
    ├── classes/                        (Compiled .class files)
    └── lib/
        ├── mysql-connector-j-8.4.0.jar (MySQL driver)
        ├── jbcrypt-0.4.jar             (Password hashing)
        └── README.md                   (Library instructions)

Setup Instructions

1. Create the Database

Open phpMyAdmin → Go to SQL tab

Copy and paste the entire contents of DATABASE_SETUP.sql and execute it.

This creates:

• electricity_billing_servlet database
• users table (stores user accounts)
• monthly_bills table (stores bill records with one bill per user per month)

Key features:

• UNIQUE constraint on (user_id, bill_month) ensures one bill per user per month
• Average is calculated dynamically using SQL AVG() function
• Foreign key ensures data integrity (deletes bills when user is deleted)

2. Download Required JAR Files

Download and place these two files in WEB-INF/lib/:

1. mysql-connector-j-8.4.0.jar

   • Download from: https://dev.mysql.com/downloads/connector/j/
   • Select version 8.4.0 from dropdown

2. jbcrypt-0.4.jar

   • Download from: http://www.mindrot.org/projects/jBCrypt/
   • Direct link: https://www.mindrot.org/files/jBCrypt/jbcrypt-0.4.jar

3. Compile Java Files

1. Open PowerShell

2. Navigate to the src folder:

   cd d:\VIT\TY\WT\Lab Codes\ElectricityBillServlet\src
   

3. Compile all Java files:

   javac -cp "C:\xampp\tomcat\lib\servlet-api.jar;..\WEB-INF\lib\mysql-connector-j-8.4.0.jar;..\WEB-INF\lib\jbcrypt-0.4.jar" -d ..\WEB-INF\classes *.java
   

If compilation succeeds, you'll see these .class files in WEB-INF/classes/:

• DBConnection.class
• HtmlUtil.class
• HomeServlet.class
• LoginServlet.class
• RegisterServlet.class
• DashboardServlet.class
• CalculateBillServlet.class
• HistoryServlet.class
• LogoutServlet.class

4. Deploy to Tomcat

Copy the entire ElectricityBillServlet folder to:

C:\xampp\tomcat\webapps\

5. Start Tomcat

Open XAMPP Control Panel → Click Start for Apache and MySQL

6. Access the Application

Open browser and navigate to:

http://localhost:8080/ElectricityBillServlet/login

Features

User Authentication

• Register: Create new account with name, email, password
• Login: Secure login using BCrypt password hashing
• Logout: End session and redirect to login

Bill Management

• Calculate Bill: Enter month and units consumed, system calculates bill

  • Rate: ₹5.50 per unit
  • Enforces: One bill per user per month

• View History: See all saved monthly bills

  • Displays month, units consumed, and bill amount
  • Shows average bill calculated from all saved records

• Dashboard: Overview of billing statistics

  • Total months with saved bills
  • Total amount paid
  • Average monthly bill

Database Schema

Users Table

id              INT (Primary Key)
name            VARCHAR(100)
email           VARCHAR(120) UNIQUE
password        VARCHAR(255) (BCrypt hashed)
created_at      TIMESTAMP

Monthly Bills Table

id              INT (Primary Key)
user_id         INT (Foreign Key → users.id)
bill_month      DATE
units           INT
bill_amount     DECIMAL(10,2)
created_at      TIMESTAMP
UNIQUE(user_id, bill_month)  -- One bill per user per month

Key Differences from PHP Version

Feature	PHP Version	Servlet Version
Framework	PHP 7+	Java Servlet (Jakarta)
Database Table	bills	monthly_bills
Date Column	bill_date DATETIME	bill_month DATE
Connection Types	Domestic/Commercial	Fixed rate (₹5.50)
Password Hashing	BCrypt ($2y$)	BCrypt ($2a$ normalized)
Session Attributes	user_email	user_id, user_name
Bill URL	/calculate.php	/calculate

Troubleshooting

Compilation Errors

• Ensure JAR files are in WEB-INF/lib/
• Check Java version (JDK 11+)
• Verify paths are correct (no spaces issues)

Database Connection Errors

• Verify MySQL is running (XAMPP Control Panel)
• Check database name: electricity_billing_servlet
• Verify credentials in DBConnection.java: user=root, password=""

Page Not Found Errors

• Verify web.xml servlet mappings
• Check URL patterns in browser match web.xml definitions
• Ensure .class files exist in WEB-INF/classes/

Login Issues

• Check password hashing is working (BCrypt)
• Verify user exists in database: SELECT * FROM users;
• Check email is correct

Development Notes

• All HTML generation is centralized in HtmlUtil.java
• All database operations use try-with-resources (auto-close)
• Input validation on both client (HTML) and server (Java) side
• Password hashing uses BCrypt with salt generation
• Session timeout follows Tomcat defaults (30 minutes)