Decisio

A lightweight Java decision DSL that replaces nested if-else with fluent rule composition, supporting AND/OR/NOT predicate logic and functional execution flows.

DSL = A specialized way of writing code that makes it feel like you are describing the problem, not programming it.

🧩 Concept

Instead of writing:

if (a) {
    if (b) {
        action1();
    }
} else {
    action2();
}

We write:

Decisio.of(value)
    .when(a).then(action1)
    .otherwise(action2);

🚀 Why Decisio?

Deeply nested if-else logic quickly becomes:

• hard to read
• difficult to maintain
• error-prone
• tightly coupled

Decisio simplifies this by providing a fluent, readable decision flow API using Java lambdas.

✨ Features

• Fluent decision API
• Replace nested if-else logic
• Predicate composition (AND / OR / NOT)
• Functional execution flow
• Lightweight (no external dependencies)
• Easy to embed in any Java project

📦 Installation

Maven

<dependency>
    <groupId>io.github.mashukbd</groupId>
    <artifactId>decisio</artifactId>
    <version>1.0.0</version>
</dependency>

🧠 Quick Example

Decisio.of(user)

    .when(Objects::isNull)
        .then(u -> guest())

    .when(User::isBlocked)
        .then(u -> blocked())

    .when(User::isAdmin)
        .and(User::isActive)
        .then(u -> admin())

    .when(User::isPremium)
        .or(User::isVip)
        .then(u -> premium())

    .otherwise(u -> normal());

🔗 Predicate Composition

AND

.when(User::isAdmin)
.and(User::isActive)

OR

.when(User::isPremium)
.or(User::isVip)

NOT

.when(User::isAdmin)
.andNot(User::isBlocked)

⚙️ How It Works

Decisio evaluates rules in order:

1. Match condition
2. Execute associated action
3. Stop (default behavior: first match wins)
4. Fallback to otherwise

🎯 Use Cases

• Business rule evaluation
• Validation flows
• Access control logic
• Decision trees
• Request routing logic
• Reducing nested conditional complexity

📌 Design Philosophy

• Keep it simple
• Stay close to Java functional style
• Avoid enterprise complexity
• Focus on readability over abstraction

⚠️ Note

Decisio is not a full rule engine or BPM system.

It is a lightweight decision composition library for everyday Java development.

📄 License

MIT License

👤 Author

Mashukur Rahman