LegacyBridge

Incremental modernization of a fictional Java application. Understand what to preserve before changing it.

Fictional scenario. Do not enter real, personal or confidential data.

Architecture of this demonstration. Different constraints can require different decisions.

Explore the demonstration

All records are fictional. This environment demonstrates engineering decisions and limits; it is not a service for real operational data.

01 · Preserve behavior
A fictional Java pricing rule mixes discounts and shipping. Freeze representative examples before changing the implementation.
02 · Characterize boundaries
Quantity 9/10, shipping thresholds and rounding have independent expected results. The API runs both Java implementations.
03 · Separate responsibilities
The modernized calculation isolates discount and shipping while retaining the result. This does not require microservices.
04 · Externalize configuration
Database and environment settings are external. Calculation code does not contain credentials.
05 · Containerize and expose an API
A Spring facade and a reproducible container provide results to the React interface.
06 · Observe and evolve
Health checks, characterization tests and a stable contract support the next controlled change. This is a focused rules-extraction example, not a full enterprise migration.

The demo illustrates a decision. Your system needs its own assessment of data, permissions, dependencies and operation.