Java Notes

Banking System — Java Programming

Build a Banking System with Java covering account management, transactions, fund transfers, and statement generation with ACID compliance.

Project Overview

The Banking System is a comprehensive Java-based application that simulates real-world banking operations including account creation, deposits, withdrawals, fund transfers, mini-statement generation, and loan management. This project demonstrates core Java concepts like OOP, exception handling, JDBC/JPA, and transaction management with ACID compliance.

This project is ideal for:

Computer Science students building portfolio projects
Java developers learning Spring Boot and REST APIs
Anyone preparing for Java developer interviews
Developers wanting to understand transaction management and ACID properties

The system supports multiple account types (Savings, Current, Fixed Deposit), implements role-based access control (Admin, Manager, Customer), and provides comprehensive reporting with PDF statement generation.

Features

Account Creation — Create savings, current, or fixed deposit accounts with KYC verification
Deposit Money — Deposit funds with real-time balance update and transaction logging
Withdraw Money — Withdraw with minimum balance validation and overdraft protection
Fund Transfer — Transfer between accounts (NEFT/IMPS/RTGS simulation) with ACID compliance
Mini Statement — View last 10 transactions with date, type, and running balance
Full Statement — Generate PDF bank statements for any date range
Balance Enquiry — Check current balance with account holder verification
Account Types — Savings (4% interest), Current (no interest, overdraft), FD (6.5% interest)
Interest Calculation — Automatic monthly interest calculation and credit for savings accounts
Loan Management — Apply for personal/home loans with EMI calculation
Role-Based Access — Admin (full access), Manager (approve/reject), Customer (own account only)
PIN Management — Set and change 4-digit transaction PIN with encryption
Account Freeze/Unfreeze — Admin can freeze suspicious accounts
Transaction History — Complete audit trail with filtering and pagination
Notifications — Email alerts for transactions above threshold amount
KYC Verification — Document upload and verification workflow
Branch Management — Multiple branches with branch-level reporting
Daily/Monthly Reports — Automated report generation for management
Exception Handling — Custom exceptions with proper HTTP status codes
Input Validation — Bean validation with custom validators for account numbers, IFSC codes

Project Structure

banking-system/ ├── src/ │ ├── main/ │ │ ├── java/com/wohotech/banking/ │ │ │ ├── BankingApplication.java │ │ │ ├── config/ │ │ │ │ ├── SecurityConfig.java │ │ │ │ ├── SwaggerConfig.java │ │ │ │ └── AppConfig.java │ │ │ ├── controller/ │ │ │ │ ├── AccountController.java │ │ │ │ ├── TransactionController.java │ │ │ │ ├── LoanController.java │ │ │ │ ├── AdminController.java │ │ │ │ └── AuthController.java │ │ │ ├── dto/ │ │ │ │ ├── request/ │ │ │ │ │ ├── AccountCreateRequest.java │ │ │ │ │ ├── DepositRequest.java │ │ │ │ │ ├── WithdrawRequest.java │ │ │ │ │ ├── TransferRequest.java │ │ │ │ │ └── LoanApplicationRequest.java │ │ │ │ └── response/ │ │ │ │ ├── AccountResponse.java │ │ │ │ ├── TransactionResponse.java │ │ │ │ ├── BalanceResponse.java │ │ │ │ └── StatementResponse.java │ │ │ ├── entity/ │ │ │ │ ├── Account.java │ │ │ │ ├── Transaction.java │ │ │ │ ├── User.java │ │ │ │ ├── Loan.java │ │ │ │ ├── Branch.java │ │ │ │ └── KycDocument.java │ │ │ ├── enums/ │ │ │ │ ├── AccountType.java │ │ │ │ ├── TransactionType.java │ │ │ │ ├── AccountStatus.java │ │ │ │ └── LoanStatus.java │ │ │ ├── exception/ │ │ │ │ ├── GlobalExceptionHandler.java │ │ │ │ ├── InsufficientBalanceException.java │ │ │ │ ├── AccountNotFoundException.java │ │ │ │ ├── InvalidPinException.java │ │ │ │ └── AccountFrozenException.java │ │ │ ├── repository/ │ │ │ │ ├── AccountRepository.java │ │ │ │ ├── TransactionRepository.java │ │ │ │ ├── UserRepository.java │ │ │ │ └── LoanRepository.java │ │ │ ├── service/ │ │ │ │ ├── AccountService.java │ │ │ │ ├── AccountServiceImpl.java │ │ │ │ ├── TransactionService.java │ │ │ │ ├── TransactionServiceImpl.java │ │ │ │ ├── LoanService.java │ │ │ │ └── StatementService.java │ │ │ └── util/ │ │ │ ├── AccountNumberGenerator.java │ │ │ ├── InterestCalculator.java │ │ │ └── PdfGenerator.java │ │ └── resources/ │ │ ├── application.yml │ │ ├── application-dev.yml │ │ ├── application-prod.yml │ │ └── data.sql │ └── test/ │ └── java/com/wohotech/banking/ │ ├── service/AccountServiceTest.java │ ├── service/TransactionServiceTest.java │ └── controller/AccountControllerTest.java ├── pom.xml ├── Dockerfile └── README.md

Database Schema

accounts Table

Column	Type	Constraints	Description
id	BIGINT	PRIMARY KEY, AUTO_INCREMENT	Unique identifier
account_number	VARCHAR(16)	UNIQUE, NOT NULL	16-digit account number
account_holder_name	VARCHAR(100)	NOT NULL	Full name of holder
account_type	ENUM	NOT NULL	SAVINGS, CURRENT, FIXED_DEPOSIT
balance	DECIMAL(15,2)	DEFAULT 0.00	Current balance
pin	VARCHAR(255)	NOT NULL	Encrypted 4-digit PIN
status	ENUM	DEFAULT 'ACTIVE'	ACTIVE, FROZEN, CLOSED
branch_id	BIGINT	FOREIGN KEY	Reference to branch
user_id	BIGINT	FOREIGN KEY	Reference to user
interest_rate	DECIMAL(4,2)	NOT NULL	Annual interest rate
min_balance	DECIMAL(10,2)	NOT NULL	Minimum required balance
created_at	TIMESTAMP	NOT NULL	Account creation date
updated_at	TIMESTAMP	NOT NULL	Last modification date

transactions Table

Column	Type	Constraints	Description
id	BIGINT	PRIMARY KEY, AUTO_INCREMENT	Unique identifier
transaction_id	VARCHAR(20)	UNIQUE, NOT NULL	TXN reference number
from_account	VARCHAR(16)	FOREIGN KEY	Source account
to_account	VARCHAR(16)	FOREIGN KEY	Destination account
amount	DECIMAL(15,2)	NOT NULL	Transaction amount
transaction_type	ENUM	NOT NULL	DEPOSIT, WITHDRAWAL, TRANSFER
description	VARCHAR(255)		Transaction description
balance_after	DECIMAL(15,2)	NOT NULL	Balance after transaction
status	ENUM	DEFAULT 'SUCCESS'	SUCCESS, FAILED, PENDING
timestamp	TIMESTAMP	NOT NULL	Transaction time

users Table

Column	Type	Constraints	Description
id	BIGINT	PRIMARY KEY, AUTO_INCREMENT	Unique identifier
email	VARCHAR(100)	UNIQUE, NOT NULL	Login email
password	VARCHAR(255)	NOT NULL	BCrypt encrypted password
full_name	VARCHAR(100)	NOT NULL	User full name
phone	VARCHAR(15)	UNIQUE	Mobile number
role	ENUM	NOT NULL	ADMIN, MANAGER, CUSTOMER
kyc_verified	BOOLEAN	DEFAULT FALSE	KYC status
created_at	TIMESTAMP	NOT NULL	Registration date

loans Table

Column	Type	Constraints	Description
id	BIGINT	PRIMARY KEY, AUTO_INCREMENT	Unique identifier
account_id	BIGINT	FOREIGN KEY	Borrower account
loan_type	ENUM	NOT NULL	PERSONAL, HOME, EDUCATION
principal_amount	DECIMAL(15,2)	NOT NULL	Loan amount
interest_rate	DECIMAL(4,2)	NOT NULL	Annual interest rate
tenure_months	INT	NOT NULL	Loan duration
emi_amount	DECIMAL(10,2)	NOT NULL	Monthly EMI
status	ENUM	DEFAULT 'PENDING'	PENDING, APPROVED, REJECTED, CLOSED
applied_date	TIMESTAMP	NOT NULL	Application date
approved_date	TIMESTAMP		Approval date

Entity Relationships

Example

User (1) ────── (N) Account Account (1) ────── (N) Transaction Account (1) ────── (N) Loan Branch (1) ────── (N) Account

Key Code Snippets

Account Entity (Model Class)

java example

package com.wohotech.banking.entity;

import jakarta.persistence.*;
import lombok.*;
import org.hibernate.annotations.CreationTimestamp;
import org.hibernate.annotations.UpdateTimestamp;
import java.math.BigDecimal;
import java.time.LocalDateTime;
import java.util.List;

@Entity
@Table(name = "accounts")
@Getter @Setter
@NoArgsConstructor @AllArgsConstructor
@Builder
public class Account {

    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    private Long id;

    @Column(name = "account_number", unique = true, nullable = false, length = 16)
    private String accountNumber;

    @Column(name = "account_holder_name", nullable = false, length = 100)
    private String accountHolderName;

    @Enumerated(EnumType.STRING)
    @Column(name = "account_type", nullable = false)
    private AccountType accountType;

    @Column(name = "balance", precision = 15, scale = 2)
    private BigDecimal balance = BigDecimal.ZERO;

    @Column(name = "pin", nullable = false)
    private String pin; // BCrypt encrypted

    @Enumerated(EnumType.STRING)
    @Column(name = "status")
    private AccountStatus status = AccountStatus.ACTIVE;

    @Column(name = "interest_rate", precision = 4, scale = 2)
    private BigDecimal interestRate;

    @Column(name = "min_balance", precision = 10, scale = 2)
    private BigDecimal minBalance;

    @ManyToOne(fetch = FetchType.LAZY)
    @JoinColumn(name = "user_id", nullable = false)
    private User user;

    @ManyToOne(fetch = FetchType.LAZY)
    @JoinColumn(name = "branch_id")
    private Branch branch;

    @OneToMany(mappedBy = "fromAccount", cascade = CascadeType.ALL, fetch = FetchType.LAZY)
    private List<Transaction> transactions;

    @CreationTimestamp
    @Column(name = "created_at", updatable = false)
    private LocalDateTime createdAt;

    @UpdateTimestamp
    @Column(name = "updated_at")
    private LocalDateTime updatedAt;
}

Account Repository

java example

package com.wohotech.banking.repository;

import com.wohotech.banking.entity.Account;
import com.wohotech.banking.enums.AccountStatus;
import com.wohotech.banking.enums.AccountType;
import org.springframework.data.jpa.repository.JpaRepository;
import org.springframework.data.jpa.repository.Query;
import org.springframework.data.repository.query.Param;
import org.springframework.stereotype.Repository;
import java.math.BigDecimal;
import java.util.List;
import java.util.Optional;

@Repository
public interface AccountRepository extends JpaRepository<Account, Long> {

    Optional<Account> findByAccountNumber(String accountNumber);

    List<Account> findByUserId(Long userId);

    List<Account> findByAccountType(AccountType accountType);

    List<Account> findByStatus(AccountStatus status);

    @Query("SELECT a FROM Account a WHERE a.balance < a.minBalance AND a.status = 'ACTIVE'")
    List<Account> findAccountsBelowMinBalance();

    @Query("SELECT SUM(a.balance) FROM Account a WHERE a.branch.id = :branchId")
    BigDecimal getTotalDepositsByBranch(@Param("branchId") Long branchId);

    @Query("SELECT a FROM Account a WHERE a.accountType = 'SAVINGS' AND a.status = 'ACTIVE'")
    List<Account> findActiveAccountsForInterestCalculation();

    boolean existsByAccountNumber(String accountNumber);
}

Account Service Implementation

Example

package com.wohotech.banking.service; import com.wohotech.banking.dto.request.AccountCreateRequest; import com.wohotech.banking.dto.request.DepositRequest; import com.wohotech.banking.dto.request.TransferRequest; import com.wohotech.banking.dto.request.WithdrawRequest; import com.wohotech.banking.dto.response.AccountResponse; import com.wohotech.banking.dto.response.BalanceResponse; import com.wohotech.banking.entity.Account; import com.wohotech.banking.entity.Transaction; import com.wohotech.banking.enums.*; import com.wohotech.banking.exception.*; import com.wohotech.banking.repository.AccountRepository; import com.wohotech.banking.repository.TransactionRepository; import com.wohotech.banking.util.AccountNumberGenerator; import lombok.RequiredArgsConstructor; import lombok.extern.slf4j.Slf4j; import org.springframework.security.crypto.password.PasswordEncoder; import org.springframework.stereotype.Service; import org.springframework.transaction.annotation.Transactional; import java.math.BigDecimal; import java.time.LocalDateTime; @Service @RequiredArgsConstructor @Slf4j public class AccountServiceImpl implements AccountService { private final AccountRepository accountRepository; private final TransactionRepository transactionRepository; private final AccountNumberGenerator accountNumberGenerator; private final PasswordEncoder passwordEncoder; @Override @Transactional public AccountResponse createAccount(AccountCreateRequest request) { log.info("Creating new account for user: {}", request.getFullName()); String accountNumber = accountNumberGenerator.generate(); Account account = Account.builder() .accountNumber(accountNumber) .accountHolderName(request.getFullName()) .accountType(request.getAccountType()) .balance(request.getInitialDeposit()) .pin(passwordEncoder.encode(request.getPin())) .status(AccountStatus.ACTIVE) .interestRate(getInterestRate(request.getAccountType())) .minBalance(getMinBalance(request.getAccountType())) .build(); Account saved = accountRepository.save(account); log.info("Account created successfully: {}", accountNumber); return mapToResponse(saved); } @Override @Transactional public BalanceResponse deposit(DepositRequest request) { Account account = accountRepository.findByAccountNumber(request.getAccountNumber()) .orElseThrow(() -> new AccountNotFoundException( "Account not found: " + request.getAccountNumber())); validateAccountActive(account); BigDecimal newBalance = account.getBalance().add(request.getAmount()); account.setBalance(newBalance); accountRepository.save(account); // Log transaction Transaction transaction = Transaction.builder() .transactionId(generateTransactionId()) .toAccount(account) .amount(request.getAmount()) .transactionType(TransactionType.DEPOSIT) .description("Cash deposit") .balanceAfter(newBalance) .status(TransactionStatus.SUCCESS) .timestamp(LocalDateTime.now()) .build(); transactionRepository.save(transaction); log.info("Deposit of {} to account {}", request.getAmount(), request.getAccountNumber()); return new BalanceResponse(account.getAccountNumber(), account.getAccountHolderName(), newBalance); } @Override @Transactional public BalanceResponse withdraw(WithdrawRequest request) { Account account = accountRepository.findByAccountNumber(request.getAccountNumber()) .orElseThrow(() -> new AccountNotFoundException( "Account not found: " + request.getAccountNumber())); validateAccountActive(account); validatePin(account, request.getPin()); BigDecimal newBalance = account.getBalance().subtract(request.getAmount()); if (newBalance.compareTo(account.getMinBalance()) < 0) { throw new InsufficientBalanceException( "Insufficient balance. Minimum balance required: " + account.getMinBalance()); } account.setBalance(newBalance); accountRepository.save(account); Transaction transaction = Transaction.builder() .transactionId(generateTransactionId()) .fromAccount(account) .amount(request.getAmount()) .transactionType(TransactionType.WITHDRAWAL) .description("Cash withdrawal") .balanceAfter(newBalance) .status(TransactionStatus.SUCCESS) .timestamp(LocalDateTime.now()) .build(); transactionRepository.save(transaction); log.info("Withdrawal of {} from account {}", request.getAmount(), request.getAccountNumber()); return new BalanceResponse(account.getAccountNumber(), account.getAccountHolderName(), newBalance); } @Override @Transactional public String transferFunds(TransferRequest request) { Account fromAccount = accountRepository.findByAccountNumber(request.getFromAccount()) .orElseThrow(() -> new AccountNotFoundException("Source account not found")); Account toAccount = accountRepository.findByAccountNumber(request.getToAccount()) .orElseThrow(() -> new AccountNotFoundException("Destination account not found")); validateAccountActive(fromAccount); validateAccountActive(toAccount); validatePin(fromAccount, request.getPin()); BigDecimal amount = request.getAmount(); BigDecimal senderNewBalance = fromAccount.getBalance().subtract(amount); if (senderNewBalance.compareTo(fromAccount.getMinBalance()) < 0) { throw new InsufficientBalanceException("Insufficient balance for transfer"); } // Debit sender fromAccount.setBalance(senderNewBalance); accountRepository.save(fromAccount); // Credit receiver BigDecimal receiverNewBalance = toAccount.getBalance().add(amount); toAccount.setBalance(receiverNewBalance); accountRepository.save(toAccount); // Log both transactions String txnId = generateTransactionId(); Transaction debitTxn = Transaction.builder() .transactionId(txnId) .fromAccount(fromAccount) .toAccount(toAccount) .amount(amount) .transactionType(TransactionType.TRANSFER) .description("Fund transfer to " + request.getToAccount()) .balanceAfter(senderNewBalance) .status(TransactionStatus.SUCCESS) .timestamp(LocalDateTime.now()) .build(); transactionRepository.save(debitTxn); log.info("Transfer of {} from {} to {} successful", amount, request.getFromAccount(), request.getToAccount()); return "Transfer successful. Transaction ID: " + txnId; } private BigDecimal getInterestRate(AccountType type) { return switch (type) { case SAVINGS -> new BigDecimal("4.00"); case CURRENT -> BigDecimal.ZERO; case FIXED_DEPOSIT -> new BigDecimal("6.50"); }; } private BigDecimal getMinBalance(AccountType type) { return switch (type) { case SAVINGS -> new BigDecimal("1000.00"); case CURRENT -> new BigDecimal("5000.00"); case FIXED_DEPOSIT -> BigDecimal.ZERO; }; } private void validateAccountActive(Account account) { if (account.getStatus() == AccountStatus.FROZEN) { throw new AccountFrozenException("Account is frozen. Contact admin."); } if (account.getStatus() == AccountStatus.CLOSED) { throw new AccountNotFoundException("Account is closed."); } } private void validatePin(Account account, String pin) { if (!passwordEncoder.matches(pin, account.getPin())) { throw new InvalidPinException("Invalid PIN entered"); } } private String generateTransactionId() { return "TXN" + System.currentTimeMillis(); } private AccountResponse mapToResponse(Account account) { return AccountResponse.builder() .accountNumber(account.getAccountNumber()) .accountHolderName(account.getAccountHolderName()) .accountType(account.getAccountType().name()) .balance(account.getBalance()) .status(account.getStatus().name()) .createdAt(account.getCreatedAt()) .build(); } }

Account Controller

java example

package com.wohotech.banking.controller;

import com.wohotech.banking.dto.request.*;
import com.wohotech.banking.dto.response.*;
import com.wohotech.banking.service.AccountService;
import com.wohotech.banking.service.StatementService;
import io.swagger.v3.oas.annotations.Operation;
import io.swagger.v3.oas.annotations.tags.Tag;
import jakarta.validation.Valid;
import lombok.RequiredArgsConstructor;
import org.springframework.http.HttpStatus;
import org.springframework.http.ResponseEntity;
import org.springframework.security.access.prepost.PreAuthorize;
import org.springframework.web.bind.annotation.*;
import java.util.List;

@RestController
@RequestMapping("/api/v1/accounts")
@RequiredArgsConstructor
@Tag(name = "Account Management", description = "APIs for banking account operations")
public class AccountController {

    private final AccountService accountService;
    private final StatementService statementService;

    @PostMapping
    @Operation(summary = "Create a new bank account")
    public ResponseEntity<AccountResponse> createAccount(
            @Valid @RequestBody AccountCreateRequest request) {
        AccountResponse response = accountService.createAccount(request);
        return new ResponseEntity<>(response, HttpStatus.CREATED);
    }

    @GetMapping("/{accountNumber}")
    @Operation(summary = "Get account details")
    public ResponseEntity<AccountResponse> getAccount(
            @PathVariable String accountNumber) {
        return ResponseEntity.ok(accountService.getAccountDetails(accountNumber));
    }

    @PostMapping("/deposit")
    @Operation(summary = "Deposit money into account")
    public ResponseEntity<BalanceResponse> deposit(
            @Valid @RequestBody DepositRequest request) {
        return ResponseEntity.ok(accountService.deposit(request));
    }

    @PostMapping("/withdraw")
    @Operation(summary = "Withdraw money from account")
    public ResponseEntity<BalanceResponse> withdraw(
            @Valid @RequestBody WithdrawRequest request) {
        return ResponseEntity.ok(accountService.withdraw(request));
    }

    @PostMapping("/transfer")
    @Operation(summary = "Transfer funds between accounts")
    public ResponseEntity<String> transfer(
            @Valid @RequestBody TransferRequest request) {
        return ResponseEntity.ok(accountService.transferFunds(request));
    }

    @GetMapping("/{accountNumber}/balance")
    @Operation(summary = "Check account balance")
    public ResponseEntity<BalanceResponse> checkBalance(
            @PathVariable String accountNumber) {
        return ResponseEntity.ok(accountService.checkBalance(accountNumber));
    }

    @GetMapping("/{accountNumber}/statement")
    @Operation(summary = "Get account mini statement (last 10 transactions)")
    public ResponseEntity<List<TransactionResponse>> getMiniStatement(
            @PathVariable String accountNumber) {
        return ResponseEntity.ok(statementService.getMiniStatement(accountNumber));
    }

    @PutMapping("/{accountNumber}/freeze")
    @PreAuthorize("hasRole('ADMIN')")
    @Operation(summary = "Freeze a bank account (Admin only)")
    public ResponseEntity<String> freezeAccount(
            @PathVariable String accountNumber) {
        accountService.freezeAccount(accountNumber);
        return ResponseEntity.ok("Account frozen successfully");
    }

    @GetMapping
    @PreAuthorize("hasRole('ADMIN') or hasRole('MANAGER')")
    @Operation(summary = "Get all accounts (Admin/Manager)")
    public ResponseEntity<List<AccountResponse>> getAllAccounts() {
        return ResponseEntity.ok(accountService.getAllAccounts());
    }
}

API Endpoints

Method	URL	Description	Auth Required
POST	`/api/v1/accounts`	Create new bank account	Yes (Any)
GET	`/api/v1/accounts/{accountNumber}`	Get account details	Yes (Owner/Admin)
POST	`/api/v1/accounts/deposit`	Deposit money	Yes (Owner)
POST	`/api/v1/accounts/withdraw`	Withdraw money (PIN required)	Yes (Owner)
POST	`/api/v1/accounts/transfer`	Fund transfer (PIN required)	Yes (Owner)
GET	`/api/v1/accounts/{accountNumber}/balance`	Check balance	Yes (Owner)
GET	`/api/v1/accounts/{accountNumber}/statement`	Mini statement	Yes (Owner)
GET	`/api/v1/accounts/{accountNumber}/statement/full`	Full PDF statement	Yes (Owner)
PUT	`/api/v1/accounts/{accountNumber}/freeze`	Freeze account	Yes (Admin)
PUT	`/api/v1/accounts/{accountNumber}/unfreeze`	Unfreeze account	Yes (Admin)
PUT	`/api/v1/accounts/{accountNumber}/pin`	Change PIN	Yes (Owner)
GET	`/api/v1/accounts`	List all accounts	Yes (Admin/Manager)
POST	`/api/v1/loans/apply`	Apply for loan	Yes (Customer)
GET	`/api/v1/loans/{loanId}`	Get loan details	Yes (Owner/Admin)
PUT	`/api/v1/loans/{loanId}/approve`	Approve loan	Yes (Manager)
GET	`/api/v1/transactions/{accountNumber}`	Transaction history	Yes (Owner)
POST	`/api/v1/auth/register`	User registration	No
POST	`/api/v1/auth/login`	User login (JWT)	No

Sample API Request & Response

POST /api/v1/accounts/transfer

Request Body:

json example

{
  "fromAccount": "1234567890123456",
  "toAccount": "6543210987654321",
  "amount": 5000.00,
  "pin": "1234",
  "description": "Rent payment for June"
}

Response (200 OK):

json example

{
  "message": "Transfer successful. Transaction ID: TXN1718192345678",
  "fromAccount": "1234567890123456",
  "newBalance": 45000.00,
  "timestamp": "2024-06-12T14:30:00"
}

Error Response (400 Bad Request):

json example

{
  "status": 400,
  "error": "INSUFFICIENT_BALANCE",
  "message": "Insufficient balance. Minimum balance required: 1000.00",
  "timestamp": "2024-06-12T14:30:00",
  "path": "/api/v1/accounts/transfer"
}

How to Run

Prerequisites

Java 17 or higher installed
MySQL 8.0 running
Maven 3.9+ installed
Git installed

Step-by-Step Setup

Step 1: Clone the repository

bash example

git clone https://github.com/wohotech/banking-system.git
cd banking-system

Step 2: Create MySQL Database

sql example

CREATE DATABASE banking_db;
CREATE USER 'banking_user'@'localhost' IDENTIFIED BY 'banking@123';
GRANT ALL PRIVILEGES ON banking_db.* TO 'banking_user'@'localhost';
FLUSH PRIVILEGES;

Step 3: Configure application.yml

yaml example

spring:
  datasource:
    url: jdbc:mysql://localhost:3306/banking_db
    username: banking_user
    password: banking@123
    driver-class-name: com.mysql.cj.jdbc.Driver
  jpa:
    hibernate:
      ddl-auto: update
    show-sql: true
    properties:
      hibernate:
        format_sql: true
        dialect: org.hibernate.dialect.MySQLDialect

jwt:
  secret: mySecretKey123456789012345678901234567890
  expiration: 86400000

server:
  port: 8080

Step 4: Build and run the application

bash example

mvn clean install
mvn spring-boot:run

Step 5: Access the application

API Base URL: http://localhost:8080/api/v1
Swagger UI: http://localhost:8080/swagger-ui.html

Step 6: Test with sample data

bash example

# Register a user
curl -X POST http://localhost:8080/api/v1/auth/register \
  -H "Content-Type: application/json" \
  -d '{"email":"john@example.com","password":"Pass@123","fullName":"John Doe","phone":"9876543210"}'

# Create an account
curl -X POST http://localhost:8080/api/v1/accounts \
  -H "Content-Type: application/json" \
  -H "Authorization: Bearer <token>" \
  -d '{"fullName":"John Doe","accountType":"SAVINGS","initialDeposit":10000,"pin":"1234"}'

Screenshots Description

Swagger UI Dashboard — Shows all available API endpoints grouped by controller with request/response schemas
Account Creation — POST request creating a savings account with initial deposit
Deposit Transaction — Successful deposit showing updated balance
Fund Transfer — Transfer between two accounts with transaction ID confirmation
Mini Statement — Last 10 transactions with date, type, amount, and running balance
Error Handling — Insufficient balance error with proper HTTP status and message
Admin Panel — List of all accounts with freeze/unfreeze controls
PDF Statement — Generated bank statement PDF with header, transactions table, and summary

Future Enhancements

Multi-Currency Support — Handle USD, EUR, GBP with real-time exchange rates
UPI Integration — Add UPI-based payment support with QR code generation
Two-Factor Authentication — OTP-based verification for high-value transactions
Scheduled Payments — Recurring payments (EMI, bills) with auto-debit
Investment Module — Mutual funds and FD booking within the app
Fraud Detection — ML-based anomaly detection for suspicious transactions
Mobile App — React Native frontend for mobile banking
Microservices Architecture — Split into Account, Transaction, Notification services
Event Sourcing — Implement event-driven architecture with Kafka
Credit Score Integration — Third-party API integration for loan eligibility

Interview Questions

Q1: How do you ensure ACID compliance in fund transfers?

Answer: We use Spring's @Transactional annotation on the transfer method. This ensures that both the debit from sender and credit to receiver happen atomically. If any step fails (e.g., receiver account not found after debit), the entire transaction rolls back. We use Isolation.SERIALIZABLE for critical operations and Propagation.REQUIRED (default) to join existing transactions.

Q2: How do you handle concurrent transactions on the same account?

Answer: We use optimistic locking with @Version annotation on the Account entity. If two transactions try to modify the same account simultaneously, one will get an OptimisticLockException. We also use @Lock(LockModeType.PESSIMISTIC_WRITE) on the repository method for critical operations like withdrawals to prevent dirty reads.

Q3: Why did you use BigDecimal instead of double for balance?

Answer: double has floating-point precision issues (e.g., 0.1 + 0.2 ≠ 0.3 in binary). In financial applications, even a fraction of a cent matters. BigDecimal provides arbitrary-precision decimal arithmetic, ensuring exact calculations. We always use BigDecimal.ZERO comparisons with compareTo() instead of equals().

Q4: How is the PIN stored securely?

Answer: The PIN is never stored in plain text. We use Spring Security's BCryptPasswordEncoder to hash the PIN before storage. During verification, we use passwordEncoder.matches(rawPin, encodedPin). BCrypt includes a random salt in each hash, so the same PIN produces different hashes, preventing rainbow table attacks.

Q5: How would you scale this system for millions of users?

Answer: (1) Database sharding by account number range, (2) Read replicas for balance enquiry and statement generation, (3) Redis caching for frequently accessed account data, (4) Message queues (Kafka) for async transaction processing, (5) Microservices decomposition with separate databases per service, (6) Connection pooling with HikariCP, (7) API rate limiting with Spring Cloud Gateway.

Q6: Explain the layered architecture used in this project.

Answer: The project follows a 4-layer architecture: Controller Layer (handles HTTP requests, input validation, response formatting), Service Layer (business logic, transaction management, orchestration), Repository Layer (data access, custom queries, pagination), Entity Layer (database mapping, relationships, constraints). This separation ensures testability, maintainability, and adherence to Single Responsibility Principle.

Q7: How do you handle exceptions in this project?

Answer: We use a @RestControllerAdvice class (GlobalExceptionHandler) that catches all exceptions and returns standardized error responses. Custom exceptions like InsufficientBalanceException, AccountNotFoundException extend RuntimeException and carry specific HTTP status codes. This approach provides consistent error format across all APIs and keeps controller code clean.

Key Learnings

Transaction management with @Transactional and rollback scenarios
Securing financial data with encryption and hashing
Implementing proper audit trails for compliance
Building RESTful APIs with proper HTTP status codes
Database design for financial systems (ACID, normalization)
Input validation and custom validators
PDF generation for reports and statements
Role-based access control with Spring Security

Exam Focus

Revise definitions, diagrams, examples, and short-answer points for Banking System — Java Programming.

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Prepare one clear explanation, one practical example, and one common mistake for this Java Master Course topic.

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Java Notes

Banking System — Java Programming

Build a Banking System with Java covering account management, transactions, fund transfers, and statement generation with ACID compliance.

Project Overview

This project is ideal for:

Computer Science students building portfolio projects
Java developers learning Spring Boot and REST APIs
Anyone preparing for Java developer interviews
Developers wanting to understand transaction management and ACID properties

Features

Account Creation — Create savings, current, or fixed deposit accounts with KYC verification
Deposit Money — Deposit funds with real-time balance update and transaction logging
Withdraw Money — Withdraw with minimum balance validation and overdraft protection
Fund Transfer — Transfer between accounts (NEFT/IMPS/RTGS simulation) with ACID compliance
Mini Statement — View last 10 transactions with date, type, and running balance
Full Statement — Generate PDF bank statements for any date range
Balance Enquiry — Check current balance with account holder verification
Account Types — Savings (4% interest), Current (no interest, overdraft), FD (6.5% interest)
Interest Calculation — Automatic monthly interest calculation and credit for savings accounts
Loan Management — Apply for personal/home loans with EMI calculation
Role-Based Access — Admin (full access), Manager (approve/reject), Customer (own account only)
PIN Management — Set and change 4-digit transaction PIN with encryption
Account Freeze/Unfreeze — Admin can freeze suspicious accounts
Transaction History — Complete audit trail with filtering and pagination
Notifications — Email alerts for transactions above threshold amount
KYC Verification — Document upload and verification workflow
Branch Management — Multiple branches with branch-level reporting
Daily/Monthly Reports — Automated report generation for management
Exception Handling — Custom exceptions with proper HTTP status codes
Input Validation — Bean validation with custom validators for account numbers, IFSC codes

Project Structure

Database Schema

accounts Table

Column	Type	Constraints	Description
id	BIGINT	PRIMARY KEY, AUTO_INCREMENT	Unique identifier
account_number	VARCHAR(16)	UNIQUE, NOT NULL	16-digit account number
account_holder_name	VARCHAR(100)	NOT NULL	Full name of holder
account_type	ENUM	NOT NULL	SAVINGS, CURRENT, FIXED_DEPOSIT
balance	DECIMAL(15,2)	DEFAULT 0.00	Current balance
pin	VARCHAR(255)	NOT NULL	Encrypted 4-digit PIN
status	ENUM	DEFAULT 'ACTIVE'	ACTIVE, FROZEN, CLOSED
branch_id	BIGINT	FOREIGN KEY	Reference to branch
user_id	BIGINT	FOREIGN KEY	Reference to user
interest_rate	DECIMAL(4,2)	NOT NULL	Annual interest rate
min_balance	DECIMAL(10,2)	NOT NULL	Minimum required balance
created_at	TIMESTAMP	NOT NULL	Account creation date
updated_at	TIMESTAMP	NOT NULL	Last modification date

transactions Table

Column	Type	Constraints	Description
id	BIGINT	PRIMARY KEY, AUTO_INCREMENT	Unique identifier
transaction_id	VARCHAR(20)	UNIQUE, NOT NULL	TXN reference number
from_account	VARCHAR(16)	FOREIGN KEY	Source account
to_account	VARCHAR(16)	FOREIGN KEY	Destination account
amount	DECIMAL(15,2)	NOT NULL	Transaction amount
transaction_type	ENUM	NOT NULL	DEPOSIT, WITHDRAWAL, TRANSFER
description	VARCHAR(255)		Transaction description
balance_after	DECIMAL(15,2)	NOT NULL	Balance after transaction
status	ENUM	DEFAULT 'SUCCESS'	SUCCESS, FAILED, PENDING
timestamp	TIMESTAMP	NOT NULL	Transaction time

users Table

Column	Type	Constraints	Description
id	BIGINT	PRIMARY KEY, AUTO_INCREMENT	Unique identifier
email	VARCHAR(100)	UNIQUE, NOT NULL	Login email
password	VARCHAR(255)	NOT NULL	BCrypt encrypted password
full_name	VARCHAR(100)	NOT NULL	User full name
phone	VARCHAR(15)	UNIQUE	Mobile number
role	ENUM	NOT NULL	ADMIN, MANAGER, CUSTOMER
kyc_verified	BOOLEAN	DEFAULT FALSE	KYC status
created_at	TIMESTAMP	NOT NULL	Registration date

loans Table

Column	Type	Constraints	Description
id	BIGINT	PRIMARY KEY, AUTO_INCREMENT	Unique identifier
account_id	BIGINT	FOREIGN KEY	Borrower account
loan_type	ENUM	NOT NULL	PERSONAL, HOME, EDUCATION
principal_amount	DECIMAL(15,2)	NOT NULL	Loan amount
interest_rate	DECIMAL(4,2)	NOT NULL	Annual interest rate
tenure_months	INT	NOT NULL	Loan duration
emi_amount	DECIMAL(10,2)	NOT NULL	Monthly EMI
status	ENUM	DEFAULT 'PENDING'	PENDING, APPROVED, REJECTED, CLOSED
applied_date	TIMESTAMP	NOT NULL	Application date
approved_date	TIMESTAMP		Approval date

Entity Relationships

Example

User (1) ────── (N) Account Account (1) ────── (N) Transaction Account (1) ────── (N) Loan Branch (1) ────── (N) Account

Key Code Snippets

Account Entity (Model Class)

java example

package com.wohotech.banking.entity;

import jakarta.persistence.*;
import lombok.*;
import org.hibernate.annotations.CreationTimestamp;
import org.hibernate.annotations.UpdateTimestamp;
import java.math.BigDecimal;
import java.time.LocalDateTime;
import java.util.List;

@Entity
@Table(name = "accounts")
@Getter @Setter
@NoArgsConstructor @AllArgsConstructor
@Builder
public class Account {

    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    private Long id;

    @Column(name = "account_number", unique = true, nullable = false, length = 16)
    private String accountNumber;

    @Column(name = "account_holder_name", nullable = false, length = 100)
    private String accountHolderName;

    @Enumerated(EnumType.STRING)
    @Column(name = "account_type", nullable = false)
    private AccountType accountType;

    @Column(name = "balance", precision = 15, scale = 2)
    private BigDecimal balance = BigDecimal.ZERO;

    @Column(name = "pin", nullable = false)
    private String pin; // BCrypt encrypted

    @Enumerated(EnumType.STRING)
    @Column(name = "status")
    private AccountStatus status = AccountStatus.ACTIVE;

    @Column(name = "interest_rate", precision = 4, scale = 2)
    private BigDecimal interestRate;

    @Column(name = "min_balance", precision = 10, scale = 2)
    private BigDecimal minBalance;

    @ManyToOne(fetch = FetchType.LAZY)
    @JoinColumn(name = "user_id", nullable = false)
    private User user;

    @ManyToOne(fetch = FetchType.LAZY)
    @JoinColumn(name = "branch_id")
    private Branch branch;

    @OneToMany(mappedBy = "fromAccount", cascade = CascadeType.ALL, fetch = FetchType.LAZY)
    private List<Transaction> transactions;

    @CreationTimestamp
    @Column(name = "created_at", updatable = false)
    private LocalDateTime createdAt;

    @UpdateTimestamp
    @Column(name = "updated_at")
    private LocalDateTime updatedAt;
}

Account Repository

java example

package com.wohotech.banking.repository;

import com.wohotech.banking.entity.Account;
import com.wohotech.banking.enums.AccountStatus;
import com.wohotech.banking.enums.AccountType;
import org.springframework.data.jpa.repository.JpaRepository;
import org.springframework.data.jpa.repository.Query;
import org.springframework.data.repository.query.Param;
import org.springframework.stereotype.Repository;
import java.math.BigDecimal;
import java.util.List;
import java.util.Optional;

@Repository
public interface AccountRepository extends JpaRepository<Account, Long> {

    Optional<Account> findByAccountNumber(String accountNumber);

    List<Account> findByUserId(Long userId);

    List<Account> findByAccountType(AccountType accountType);

    List<Account> findByStatus(AccountStatus status);

    @Query("SELECT a FROM Account a WHERE a.balance < a.minBalance AND a.status = 'ACTIVE'")
    List<Account> findAccountsBelowMinBalance();

    @Query("SELECT SUM(a.balance) FROM Account a WHERE a.branch.id = :branchId")
    BigDecimal getTotalDepositsByBranch(@Param("branchId") Long branchId);

    @Query("SELECT a FROM Account a WHERE a.accountType = 'SAVINGS' AND a.status = 'ACTIVE'")
    List<Account> findActiveAccountsForInterestCalculation();

    boolean existsByAccountNumber(String accountNumber);
}

Account Service Implementation

Example

Account Controller

java example

package com.wohotech.banking.controller;

import com.wohotech.banking.dto.request.*;
import com.wohotech.banking.dto.response.*;
import com.wohotech.banking.service.AccountService;
import com.wohotech.banking.service.StatementService;
import io.swagger.v3.oas.annotations.Operation;
import io.swagger.v3.oas.annotations.tags.Tag;
import jakarta.validation.Valid;
import lombok.RequiredArgsConstructor;
import org.springframework.http.HttpStatus;
import org.springframework.http.ResponseEntity;
import org.springframework.security.access.prepost.PreAuthorize;
import org.springframework.web.bind.annotation.*;
import java.util.List;

@RestController
@RequestMapping("/api/v1/accounts")
@RequiredArgsConstructor
@Tag(name = "Account Management", description = "APIs for banking account operations")
public class AccountController {

    private final AccountService accountService;
    private final StatementService statementService;

    @PostMapping
    @Operation(summary = "Create a new bank account")
    public ResponseEntity<AccountResponse> createAccount(
            @Valid @RequestBody AccountCreateRequest request) {
        AccountResponse response = accountService.createAccount(request);
        return new ResponseEntity<>(response, HttpStatus.CREATED);
    }

    @GetMapping("/{accountNumber}")
    @Operation(summary = "Get account details")
    public ResponseEntity<AccountResponse> getAccount(
            @PathVariable String accountNumber) {
        return ResponseEntity.ok(accountService.getAccountDetails(accountNumber));
    }

    @PostMapping("/deposit")
    @Operation(summary = "Deposit money into account")
    public ResponseEntity<BalanceResponse> deposit(
            @Valid @RequestBody DepositRequest request) {
        return ResponseEntity.ok(accountService.deposit(request));
    }

    @PostMapping("/withdraw")
    @Operation(summary = "Withdraw money from account")
    public ResponseEntity<BalanceResponse> withdraw(
            @Valid @RequestBody WithdrawRequest request) {
        return ResponseEntity.ok(accountService.withdraw(request));
    }

    @PostMapping("/transfer")
    @Operation(summary = "Transfer funds between accounts")
    public ResponseEntity<String> transfer(
            @Valid @RequestBody TransferRequest request) {
        return ResponseEntity.ok(accountService.transferFunds(request));
    }

    @GetMapping("/{accountNumber}/balance")
    @Operation(summary = "Check account balance")
    public ResponseEntity<BalanceResponse> checkBalance(
            @PathVariable String accountNumber) {
        return ResponseEntity.ok(accountService.checkBalance(accountNumber));
    }

    @GetMapping("/{accountNumber}/statement")
    @Operation(summary = "Get account mini statement (last 10 transactions)")
    public ResponseEntity<List<TransactionResponse>> getMiniStatement(
            @PathVariable String accountNumber) {
        return ResponseEntity.ok(statementService.getMiniStatement(accountNumber));
    }

    @PutMapping("/{accountNumber}/freeze")
    @PreAuthorize("hasRole('ADMIN')")
    @Operation(summary = "Freeze a bank account (Admin only)")
    public ResponseEntity<String> freezeAccount(
            @PathVariable String accountNumber) {
        accountService.freezeAccount(accountNumber);
        return ResponseEntity.ok("Account frozen successfully");
    }

    @GetMapping
    @PreAuthorize("hasRole('ADMIN') or hasRole('MANAGER')")
    @Operation(summary = "Get all accounts (Admin/Manager)")
    public ResponseEntity<List<AccountResponse>> getAllAccounts() {
        return ResponseEntity.ok(accountService.getAllAccounts());
    }
}

API Endpoints

Method	URL	Description	Auth Required
POST	`/api/v1/accounts`	Create new bank account	Yes (Any)
GET	`/api/v1/accounts/{accountNumber}`	Get account details	Yes (Owner/Admin)
POST	`/api/v1/accounts/deposit`	Deposit money	Yes (Owner)
POST	`/api/v1/accounts/withdraw`	Withdraw money (PIN required)	Yes (Owner)
POST	`/api/v1/accounts/transfer`	Fund transfer (PIN required)	Yes (Owner)
GET	`/api/v1/accounts/{accountNumber}/balance`	Check balance	Yes (Owner)
GET	`/api/v1/accounts/{accountNumber}/statement`	Mini statement	Yes (Owner)
GET	`/api/v1/accounts/{accountNumber}/statement/full`	Full PDF statement	Yes (Owner)
PUT	`/api/v1/accounts/{accountNumber}/freeze`	Freeze account	Yes (Admin)
PUT	`/api/v1/accounts/{accountNumber}/unfreeze`	Unfreeze account	Yes (Admin)
PUT	`/api/v1/accounts/{accountNumber}/pin`	Change PIN	Yes (Owner)
GET	`/api/v1/accounts`	List all accounts	Yes (Admin/Manager)
POST	`/api/v1/loans/apply`	Apply for loan	Yes (Customer)
GET	`/api/v1/loans/{loanId}`	Get loan details	Yes (Owner/Admin)
PUT	`/api/v1/loans/{loanId}/approve`	Approve loan	Yes (Manager)
GET	`/api/v1/transactions/{accountNumber}`	Transaction history	Yes (Owner)
POST	`/api/v1/auth/register`	User registration	No
POST	`/api/v1/auth/login`	User login (JWT)	No

Sample API Request & Response

POST /api/v1/accounts/transfer

Request Body:

json example

{
  "fromAccount": "1234567890123456",
  "toAccount": "6543210987654321",
  "amount": 5000.00,
  "pin": "1234",
  "description": "Rent payment for June"
}

Response (200 OK):

json example

{
  "message": "Transfer successful. Transaction ID: TXN1718192345678",
  "fromAccount": "1234567890123456",
  "newBalance": 45000.00,
  "timestamp": "2024-06-12T14:30:00"
}

Error Response (400 Bad Request):

json example

{
  "status": 400,
  "error": "INSUFFICIENT_BALANCE",
  "message": "Insufficient balance. Minimum balance required: 1000.00",
  "timestamp": "2024-06-12T14:30:00",
  "path": "/api/v1/accounts/transfer"
}

How to Run

Prerequisites

Java 17 or higher installed
MySQL 8.0 running
Maven 3.9+ installed
Git installed

Step-by-Step Setup

Step 1: Clone the repository

bash example

git clone https://github.com/wohotech/banking-system.git
cd banking-system

Step 2: Create MySQL Database

sql example

CREATE DATABASE banking_db;
CREATE USER 'banking_user'@'localhost' IDENTIFIED BY 'banking@123';
GRANT ALL PRIVILEGES ON banking_db.* TO 'banking_user'@'localhost';
FLUSH PRIVILEGES;

Step 3: Configure application.yml

yaml example

spring:
  datasource:
    url: jdbc:mysql://localhost:3306/banking_db
    username: banking_user
    password: banking@123
    driver-class-name: com.mysql.cj.jdbc.Driver
  jpa:
    hibernate:
      ddl-auto: update
    show-sql: true
    properties:
      hibernate:
        format_sql: true
        dialect: org.hibernate.dialect.MySQLDialect

jwt:
  secret: mySecretKey123456789012345678901234567890
  expiration: 86400000

server:
  port: 8080

Step 4: Build and run the application

bash example

mvn clean install
mvn spring-boot:run

Step 5: Access the application

API Base URL: http://localhost:8080/api/v1
Swagger UI: http://localhost:8080/swagger-ui.html

Step 6: Test with sample data

bash example

# Register a user
curl -X POST http://localhost:8080/api/v1/auth/register \
  -H "Content-Type: application/json" \
  -d '{"email":"john@example.com","password":"Pass@123","fullName":"John Doe","phone":"9876543210"}'

# Create an account
curl -X POST http://localhost:8080/api/v1/accounts \
  -H "Content-Type: application/json" \
  -H "Authorization: Bearer <token>" \
  -d '{"fullName":"John Doe","accountType":"SAVINGS","initialDeposit":10000,"pin":"1234"}'

Screenshots Description

Swagger UI Dashboard — Shows all available API endpoints grouped by controller with request/response schemas
Account Creation — POST request creating a savings account with initial deposit
Deposit Transaction — Successful deposit showing updated balance
Fund Transfer — Transfer between two accounts with transaction ID confirmation
Mini Statement — Last 10 transactions with date, type, amount, and running balance
Error Handling — Insufficient balance error with proper HTTP status and message
Admin Panel — List of all accounts with freeze/unfreeze controls
PDF Statement — Generated bank statement PDF with header, transactions table, and summary

Future Enhancements

Multi-Currency Support — Handle USD, EUR, GBP with real-time exchange rates
UPI Integration — Add UPI-based payment support with QR code generation
Two-Factor Authentication — OTP-based verification for high-value transactions
Scheduled Payments — Recurring payments (EMI, bills) with auto-debit
Investment Module — Mutual funds and FD booking within the app
Fraud Detection — ML-based anomaly detection for suspicious transactions
Mobile App — React Native frontend for mobile banking
Microservices Architecture — Split into Account, Transaction, Notification services
Event Sourcing — Implement event-driven architecture with Kafka
Credit Score Integration — Third-party API integration for loan eligibility

Interview Questions

Q1: How do you ensure ACID compliance in fund transfers?

Q2: How do you handle concurrent transactions on the same account?

Q3: Why did you use BigDecimal instead of double for balance?

Q4: How is the PIN stored securely?

Q5: How would you scale this system for millions of users?

Q6: Explain the layered architecture used in this project.

Q7: How do you handle exceptions in this project?

Key Learnings

Transaction management with @Transactional and rollback scenarios
Securing financial data with encryption and hashing
Implementing proper audit trails for compliance
Building RESTful APIs with proper HTTP status codes
Database design for financial systems (ACID, normalization)
Input validation and custom validators
PDF generation for reports and statements
Role-based access control with Spring Security

Exam Focus

Revise definitions, diagrams, examples, and short-answer points for Banking System — Java Programming.

Interview Use

Prepare one clear explanation, one practical example, and one common mistake for this Java Master Course topic.

Search Terms

java-master-course, java master course, java, master, course, projects, banking, system

Continue learning this concept

PreviousString Programs — Practice NextChat Application