A Simple & Intuitive Rules Abstraction for Java

RuleBook brings a lightweight, lambda-enabled Domain Specific Language (DSL) to Java, simplifying the way developers define and manage rules in their applications. If you find yourself wrestling with complex nested if-else statements, it’s time to explore RuleBook. This article will guide you through getting started with RuleBook, setting it up in your projects, and using its powerful features effectively.

Getting Started with RuleBook

• 1. Getting RuleBook
• 2. Using RuleBook
• 3. The RuleBook Domain Specific Language
• 4. POJO Rules
• 5. Using RuleBook with Spring

1. Getting RuleBook

Installing RuleBook is a walk in the park, whether you’re working with Maven or Gradle. Follow these steps:

1.1 Building RuleBook

bash
git clone https://github.com/Clayton7510/RuleBook.git
cd RuleBook
./gradlew build

1.2 Adding RuleBook to Your Project

For Maven projects, include the following dependency in your pom.xml:

<dependency>
    <groupId>com.deliveredtechnologies</groupId>
    <artifactId>rulebook-core</artifactId>
    <version>0.12</version>
</dependency>

1.3 Adding RuleBook to Your Gradle Project

For Gradle projects, simply include this in your build.gradle:

dependencies {
    compile 'com.deliveredtechnologies:rulebook-core:0.12'
}

2. Using RuleBook

Now that you have installed RuleBook, let’s see how to use it. Think of RuleBook as a chef in a kitchen, where you get to define the unique recipes (rules) that the chef follows to prepare the perfect dish (final results).

2.1 A Hello World Example

To make your first RuleBook, imagine that each rule is a part of your recipe. Here’s how to bake a simple “Hello World” cake:

java
RuleBook ruleBook = RuleBookBuilder.create()
    .addRule(rule - rule.withNoSpecifiedFactType()
        .then(f - System.out.print("Hello "))
        .then(f - System.out.println("World")))
    .build();

ruleBook.run(new FactMap());

2.2 Using Facts

Now, let’s see how we can use facts. Imagine facts as ingredients needed for our recipe. Here’s a quick example:

java
RuleBook ruleBook = RuleBookBuilder.create()
    .addRule(rule - rule.withFactType(String.class)
        .when(f - f.containsKey("hello"))
        .using("hello")
        .then(System.out::print))
    .addRule(rule - rule.withFactType(String.class)
        .when(f - f.containsKey("world"))
        .using("world")
        .then(System.out::println))
    .build();

NameValueReferableMap factMap = new FactMap();
factMap.setValue("hello", "Hello");
factMap.setValue("world", "World");
ruleBook.run(factMap);

3. The RuleBook Domain Specific Language

RuleBook uses a familiar Given-When-Then structure, similar to many behavior-driven development (BDD) frameworks. Think of it as the instruction manual for our kitchen. Here’s how it breaks down:

• Given – These are the facts (ingredients) you start with.
• When – This describes the conditions for the rules (actions to take).
• Then – This dictates the actions that occur if the conditions are satisfied (resulting outcomes).

4. POJO Rules

POJO Rules allow you to define rules more intuitively using annotations, much like labeling ingredients in our kitchen. Here’s a brief example:

java
@Rule
public class HelloWorld {
    @Given("hello")
    private String hello;
    @Given("world")
    private String world;

    @Then
    public RuleState then() {
        System.out.println(hello + " " + world);
        return RuleState.BREAK;
    }
}

5. Using RuleBook with Spring

Integrating RuleBook with Spring is like using a sous-chef to help manage the various components of your kitchen. To get started:

5.1 Adding Spring Support

Simply add rulebook-spring as a dependency in your project:

<dependency>
    <groupId>com.deliveredtechnologies</groupId>
    <artifactId>rulebook-spring</artifactId>
    <version>0.12</version>
</dependency>

Troubleshooting

If you encounter any issues during installation or while writing rules, consider the following troubleshooting tips:

• Ensure that your project is properly configured to use Maven or Gradle.
• Check for typos in your code, especially in rule definitions.
• Look for missing dependencies or incorrect versions.
• Refer to the Wiki for more guidance.

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