Running Your Decision Table¶

This guide shows you how to load and execute a decision table in a Java application.

Creating the Java Application¶

Let's create a simple Java application that loads our shipping charges decision table and executes it with test data.

Main Application Class¶

Create a class called DecisionTableExample.java:

package com.example;

import com.example.model.Charge;
import com.example.model.Order;
import org.kie.api.KieServices;
import org.kie.api.builder.KieBuilder;
import org.kie.api.builder.KieFileSystem;
import org.kie.api.builder.KieRepository;
import org.kie.api.builder.Message.Level;
import org.kie.api.runtime.KieContainer;
import org.kie.api.runtime.KieSession;
import org.kie.internal.io.ResourceFactory;

import java.util.ArrayList;
import java.util.List;

public class DecisionTableExample {

    public static void main(String[] args) {
        try {
            // Setup KIE resources
            KieServices kieServices = KieServices.Factory.get();
            KieFileSystem kfs = kieServices.newKieFileSystem();
            kfs.write(ResourceFactory.newClassPathResource("rules/ShippingCharges.drl.xlsx"));

            KieBuilder kieBuilder = kieServices.newKieBuilder(kfs);
            kieBuilder.buildAll();

            if (kieBuilder.getResults().hasMessages(Level.ERROR)) {
                throw new RuntimeException("Build Errors:\n" + kieBuilder.getResults().toString());
            }

            KieRepository kieRepository = kieServices.getRepository();
            KieContainer kieContainer = kieServices.newKieContainer(kieRepository.getDefaultReleaseId());

            // Create a new session and run test scenarios
            testShippingCharge(kieContainer, 2, 150.0, 1, "Next-day shipping, under $300, 2 items");
            testShippingCharge(kieContainer, 5, 150.0, 2, "2-day shipping, under $300, 5 items");
            testShippingCharge(kieContainer, 3, 350.0, 3, "Standard shipping, over $300, 3 items");
            testShippingCharge(kieContainer, 5, 400.0, 5, "Standard shipping, over $300, 5 items (free)");

        } catch (Exception e) {
            e.printStackTrace();
        }
    }

    private static void testShippingCharge(KieContainer kieContainer, int items, double total, int days, String description) {
        System.out.println("\nTesting: " + description);

        // Create a new session for each test to avoid rule interference
        KieSession kieSession = kieContainer.newKieSession();

        // Create a new order with the test parameters
        Order order = new Order(items, total, days);
        System.out.printf("Order: %d items, $%.2f total, %d delivery days\n",
                order.getItemsCount(), order.getTotal(), order.getDeliverInDays());

        // Insert the facts and fire the rules
        kieSession.insert(order);
        kieSession.fireAllRules();

        // Collect and display results
        List<Charge> charges = new ArrayList<>();
        kieSession.getObjects(obj -> obj instanceof Charge)
                .forEach(obj -> charges.add((Charge) obj));

        if (charges.isEmpty()) {
            System.out.println("No shipping charge calculated!");
        } else {
            System.out.printf("Shipping Charge: $%.2f\n", charges.get(0).getAmount());
        }

        // Clean up
        kieSession.dispose();
    }
}

Understanding the Code¶

Let's break down the important parts of this example:

Setup and Build the Knowledge Base¶

// Setup KIE resources
KieServices kieServices = KieServices.Factory.get();
KieFileSystem kfs = kieServices.newKieFileSystem();
kfs.write(ResourceFactory.newClassPathResource("rules/ShippingCharges.drl.xlsx"));

KieBuilder kieBuilder = kieServices.newKieBuilder(kfs);
kieBuilder.buildAll();

if (kieBuilder.getResults().hasMessages(Level.ERROR)) {
    throw new RuntimeException("Build Errors:\n" + kieBuilder.getResults().toString());
}

KieRepository kieRepository = kieServices.getRepository();
KieContainer kieContainer = kieServices.newKieContainer(kieRepository.getDefaultReleaseId());

This code: 1. Gets a KIE services instance 2. Creates a virtual file system to hold the rules 3. Loads the decision table from the classpath 4. Builds the knowledge base 5. Checks for any build errors 6. Creates a container that holds the compiled rules

Testing with Different Scenarios¶

testShippingCharge(kieContainer, 2, 150.0, 1, "Next-day shipping, under $300, 2 items");
testShippingCharge(kieContainer, 5, 150.0, 2, "2-day shipping, under $300, 5 items");
testShippingCharge(kieContainer, 3, 350.0, 3, "Standard shipping, over $300, 3 items");
testShippingCharge(kieContainer, 5, 400.0, 5, "Standard shipping, over $300, 5 items (free)");

This runs four different test cases with varying: - Number of items - Order total - Delivery days

The Test Method¶

private static void testShippingCharge(KieContainer kieContainer, int items, double total, int days, String description) {
    System.out.println("\nTesting: " + description);

    // Create a new session for each test to avoid rule interference
    KieSession kieSession = kieContainer.newKieSession();

    // Create a new order with the test parameters
    Order order = new Order(items, total, days);
    System.out.printf("Order: %d items, $%.2f total, %d delivery days\n",
            order.getItemsCount(), order.getTotal(), order.getDeliverInDays());

    // Insert the facts and fire the rules
    kieSession.insert(order);
    kieSession.fireAllRules();

    // Collect and display results
    List<Charge> charges = new ArrayList<>();
    kieSession.getObjects(obj -> obj instanceof Charge)
            .forEach(obj -> charges.add((Charge) obj));

    if (charges.isEmpty()) {
        System.out.println("No shipping charge calculated!");
    } else {
        System.out.printf("Shipping Charge: $%.2f\n", charges.get(0).getAmount());
    }

    // Clean up
    kieSession.dispose();
}

For each test case, this method: 1. Creates a new KIE session (a working memory for rules) 2. Creates an Order object with the test parameters 3. Inserts the order into the session 4. Fires all the rules to calculate the shipping charge 5. Collects any Charge objects that were created 6. Displays the results 7. Disposes of the session to free resources

Running the Application¶

You can run this application by executing the main method in your IDE or by building and running the JAR file.

Expected Output¶

When you run the application, you should see output similar to this:

Testing: Next-day shipping, under $300, 2 items
Order: 2 items, $150.00 total, 1 delivery days
Shipping Charge: $35.00

Testing: 2-day shipping, under $300, 5 items
Order: 5 items, $150.00 total, 2 delivery days
Shipping Charge: $17.50

Testing: Standard shipping, over $300, 3 items
Order: 3 items, $350.00 total, 3 delivery days
Shipping Charge: $4.50

Testing: Standard shipping, over $300, 5 items (free)
Order: 5 items, $400.00 total, 5 delivery days
Shipping Charge: $0.00

Alternative Loading Method¶

For simpler applications, you can also use the SpreadsheetCompiler directly:

// Alternative loading method using SpreadsheetCompiler
SpreadsheetCompiler compiler = new SpreadsheetCompiler();
String drl = compiler.compile(ResourceFactory.newClassPathResource("rules/ShippingCharges.drl.xlsx"),
                             InputType.XLS);

KieHelper kieHelper = new KieHelper();
kieHelper.addContent(drl, ResourceType.DRL);
KieContainer kieContainer = kieHelper.getKieContainer();

This method: 1. Creates a SpreadsheetCompiler instance 2. Compiles the decision table directly to DRL (Drools Rule Language) 3. Creates a KieHelper to add the compiled DRL 4. Gets a KieContainer from the helper

Next Steps¶

Now that you know how to create and run a decision table, you can:

Modify the existing rules to change the shipping charges
Add more conditions like customer type or destination region
Create more complex decision tables for other business scenarios

In the next section, we'll explore the RuleSet definitions in more detail.

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