Article series · 6 articles

SOLID in MuleSoft

An introduction and five principles applied to MuleSoft integrations, with before-and-after examples and MUnit tests.

Reading order

1. Part 1 of 6

   SOLID in MuleSoft: what carries over from object-oriented design, and what doesn't

   A code-backed look at the five SOLID principles in Mule 4 — where each one fits integration work, where it needs translating, and where it stops being useful.

2. Part 2 of 6

   Single Responsibility in MuleSoft: one reason to change per flow

   SRP is not about small flows. It is about grouping logic by the reason it changes — shown with a Mule 4 order flow before and after, with MUnit tests.

3. Part 3 of 6

   Open/Closed in MuleSoft: extending without editing, and what it costs

   Adding a payment method to a Mule 4 app without touching the router — with config-driven dynamic routing, MUnit evidence, and an honest look at the trade-offs.

4. Part 4 of 6

   Liskov Substitution in MuleSoft: implementations that can replace each other

   Mule has no inheritance, but LSP still bites: two adapters behind one contract, where the new one keeps the field names and quietly changes their meaning.

5. Part 5 of 6

   Interface Segregation in MuleSoft: an API for each consumer

   One order endpoint that returns everything to everyone, split into consumer-shaped interfaces — and why the strongest argument for ISP in integration is data exposure.

6. Part 6 of 6

   Dependency Inversion in MuleSoft: business flows that own their abstractions

   DIP is not externalised configuration. It is the business flow defining the model it needs and adapters conforming to it — shown in Mule 4 with swappable ERP and in-memory implementations.