Getting Started with Drools Decision Tables

Project Setup

Before diving into decision tables, you need to set up your Java project with the necessary dependencies. This guide will walk you through the process step by step.

Maven Configuration

Below is a complete pom.xml configuration you can use as a starting point for your Drools decision table project:

<?xml version="1.0" encoding="UTF-8"?>
<project xmlns="http://maven.apache.org/POM/4.0.0"
         xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
         xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
    <modelVersion>4.0.0</modelVersion>

    <groupId>ai.aletyx.example</groupId>
    <artifactId>drools-decision-tables</artifactId>
    <version>1.0-SNAPSHOT</version>

    <properties>
        <maven.compiler.source>17 </maven.compiler.source>
        <maven.compiler.target>17</maven.compiler.target>
        <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
        <drools.version>10.0.0</drools.version>
        <slf4j.version>2.0.9</slf4j.version>
    </properties>

    <dependencies>
        <!-- Drools Dependencies -->
        <dependency>
            <groupId>org.kie</groupId>
            <artifactId>kie-api</artifactId>
            <version>${drools.version}</version>
        </dependency>
        <dependency>
            <groupId>org.drools</groupId>
            <artifactId>drools-core</artifactId>
            <version>${drools.version}</version>
        </dependency>
        <dependency>
            <groupId>org.drools</groupId>
            <artifactId>drools-compiler</artifactId>
            <version>${drools.version}</version>
        </dependency>
        <dependency>
            <groupId>org.drools</groupId>
            <artifactId>drools-mvel</artifactId>
            <version>${drools.version}</version>
        </dependency>

        <!-- Decision Tables -->
        <dependency>
            <groupId>org.drools</groupId>
            <artifactId>drools-decisiontables</artifactId>
            <version>${drools.version}</version>
        </dependency>

        <!-- Required for Excel support -->
        <dependency>
            <groupId>org.apache.poi</groupId>
            <artifactId>poi</artifactId>
            <version>5.2.3</version>
        </dependency>
        <dependency>
            <groupId>org.apache.poi</groupId>
            <artifactId>poi-ooxml</artifactId>
            <version>5.2.3</version>
        </dependency>

        <!-- Logging Dependencies -->
        <dependency>
            <groupId>org.slf4j</groupId>
            <artifactId>slf4j-api</artifactId>
            <version>${slf4j.version}</version>
        </dependency>
        <dependency>
            <groupId>org.slf4j</groupId>
            <artifactId>slf4j-simple</artifactId>
            <version>${slf4j.version}</version>
        </dependency>

        <!-- Testing -->
        <dependency>
            <groupId>junit</groupId>
            <artifactId>junit</artifactId>
            <version>4.13.2</version>
            <scope>test</scope>
        </dependency>
    </dependencies>

    <build>
        <plugins>
            <plugin>
                <groupId>org.apache.maven.plugins</groupId>
                <artifactId>maven-compiler-plugin</artifactId>
                <version>3.11.0</version>
                <configuration>
                    <source>${maven.compiler.source}</source>
                    <target>${maven.compiler.target}</target>
                </configuration>
            </plugin>
        </plugins>
    </build>
</project>

Drools Excel Spreadsheet Filename Change Requirement

Important Note: When migrating from Drools 7 or earlier, spreadsheet decision table files must use the extension .drl.xls, .drl.xlsx, or .drl.csv. This is important to note as historically in earlier versions of Drools, you could use decisiontable.xls and the project would incorporate them, now they must be explicitly defined this way. This does not affect usage in your spreadsheet editor of choice, it is mainly designed as a semantical parser/cpompiler requirement to Drools.

Potential Logging Error: StatusLogger Log4j2 could not find a loggin implementation

When including drools-decisiontables in your project, you might encounter the following error:

ERROR StatusLogger Log4j2 could not find a logging implementation

This happens because Apache POI (used to process spreadsheet files) uses the Log4j API. To avoid this error, you need to include either: 1. The SLF4J adapter (included in the above POM) 2. 2. Or the Log4j 2 SLF4J Binding, if you're using Log4j as your logging backend

Project Structure

Here's a recommended project structure for a basic Drools decision table application:

src/
├── main/
│   ├── java/
│   │   └── com/
│   │       └── example/
│   │           ├── model/
│   │           │   └── Order.java
│   │           └── DecisionTableExample.java
│   └── resources/
│       └── rules/
│           └── ShippingCharges.drl.xlsx
└── test/
    └── java/
        └── com/
            └── example/
                └── DecisionTableTest.java

Next Steps

Now that you have your project set up, continue to the next section to create your first decision table in Excel.

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