Data Source Migration: Legacy to Modern

A small Spring Boot loan management application that currently connects to a legacy data warehouse (simulated via H2 with legacy-style schemas). The workshop challenge is to migrate the data source to a modern schema while keeping the application functional.

Overview

This app manages loan data: borrowers, loan products, loan accounts, and payment history. It currently reads from legacy tables with denormalized structures, cryptic column names, and outdated patterns. The goal is to rewire it to use a normalized modern schema with clear naming conventions.

Architecture

┌─────────────────────────────┐
│   Loan Service (Spring Boot)│
│                             │
│  Controllers ─► Services    │
│                  │          │
│              Repositories   │
│                  │          │
│         Legacy DataSource   │  ← YOU ARE HERE
│         (H2 / legacy schema)│
│                             │
│         Modern DataSource   │  ← MIGRATE TO HERE
│         (H2 / modern schema)│
└─────────────────────────────┘

Current State (Legacy)

The app connects to legacy tables:

• CDW_BORR_MSTR — Borrower master (denormalized, cryptic columns)
• CDW_LN_PROD — Loan products
• CDW_LN_ACCT — Loan accounts (wide table with embedded borrower data)
• CDW_PMT_HIST — Payment history

See data/legacy-schema/ for full DDL and data/mappings/ for column-level mappings.

Target State (Modern)

Migrate to normalized tables:

• borrowers — Clean borrower records
• loan_products — Product catalog
• loan_accounts — Normalized loan accounts with foreign keys
• payments — Payment records

See data/modern-schema/ for target DDL.

Quick Start

./mvnw spring-boot:run

The app runs on http://localhost:8080 with endpoints:

• GET /api/loans — List all loans
• GET /api/loans/{id} — Get loan details
• GET /api/borrowers — List borrowers
• GET /api/borrowers/{id} — Get borrower with loans
• GET /api/payments/loan/{loanId} — Payment history for a loan

Tech Stack

• Java 17
• Spring Boot 3.2
• Spring Data JPA
• H2 (in-memory, simulating legacy DW)
• Maven

License

MIT