Master Drools Programming - Learn How to Write Drools Rules

Name: Master Drools Programming - Learn How to Write Drools Rules
Rating: 4.6 (2058 reviews)

Learn how to run and write rules for Apache Drools Rule Engine and how to work with spredsheet decision tables

Created byJuhan Aasaru

Last updated 3/2025

English

What you'll learn

Program rules in Drools 7 domain specific language
Learn Drools language constructs like insert, modify, exists, forall, insertLogical, salience, agenda-group etc
Create spreadsheet decision tables and spreadsheet templates
What is Complex Event Processing and how Drools handles it
How to use rule templates (DRT or Freemarker) and run dynamically defined DRL
Understand different Drools running modes (active/passive, cloud/stream, sequential)
How Drools works internally and what to keep in mind for writing faster performing rules

Course content

13 sections • 99 lectures • 7h 51m total length

Introduction to the course1:02
What is a Rule Engine?11:10
How to Design Rules and When (not) to Use Drools3:39
Introduction to Drools Language Syntax7:34

Structure of Example Code5:18
We look at the example code I have created in Github: https://github.com/aasaru/drools-training
You need JDK 17 or JDK 19 to run this code.
Drools New Syntax - OOPath0:11
Get example code running with IntelliJ IDEA Community Edition4:46
Get example code running with Eclipse5:23
NB! After filming this part newer Drools version has been released and I have updated the source code. Please open pom.xml and find out the correct version.
Get example code running with Visual Studio Code (VS Code)4:33

Intro to Adding New Facts & Setting Execution Order1:07
Rule Dialect Change0:37
You can write Drools rules in either "java" or in "mvel" dialect.
Here I explain the difference of them and why I changed section06 code to use "java" dialect.
Note about upcoming Step0:20
Step1: Create a New Fact and Insert it into the Session5:35
Step2: Control execution order with salience4:50
Step3: Control execution order with agenda groups13:48
Step4: Use agenda groups with salience4:47
Step5: Run a single rule from an activation group8:06
Bonus Step! Step 6. Set Focus to Agenda Group In Drools Rule.0:44
In this self-assignment you learn how to set focus to agenda group in the rules.

I have added this assignment after publishing the course. You may need to run "git pull" to get the latest code. It comes without a video and you must examine the rules and Java code yourself.
Summary of Adding Facts and Setting Execution Order1:30

Introduction to Logical Insertion of Facts and Checking the Fact Does Not Exist1:35
Step1: Add Fact Using insertLogical()6:31
Using the optional "this" keyword on the left-hand-side of MVEL rules0:18
Step2: Create fact objects and check that fact does not exist7:25
Step3: Replace Changing of the Objects with Fact Objects6:24
Step4: Reduce the Number of Rules Needed by Eliminating Positive Cases3:40
Section Summary1:23

Spreadsheet decision tables intro11:07
A new GitHub repository for code examples4:04
Starting this section the code examples are taken from another Git repository. In this lecture, I will give an overview of how this repository differs from the previous one.
Basic layout of a spreadsheet decision table10:07
Defining multiple action columns in a spreadsheet4:43
Using formulas in a spreadsheet decision table6:29
Set a custom DRL rule name and add a comment5:02
How to place several rule tables in one spreadsheet4:20
Multiple rule tables in one spreadsheet. Several parameters in a single cell.4:40
Join multiple fact objects in a spreadsheet decision table8:04
Using forall construct as a condition in spreadsheet decision tables9:46
Condition without a pattern in a spreadsheet decision table3:54
Set rule priority in a spreadsheet decision table8:13
Sequential attribute in RuleSet4:42
Using activation groups in spreadsheet decision tables8:44
Drools sequential mode9:30
Using custom labels in spreadsheet decision tables6:06
Recap Spreadsheet Decision Tables1:00

Rule templates intro3:13
Using Drools Rule Templates (DRT) for creating rules16:38
Fetching template placeholder values from a tabular data source6:24
Use Freemarker templates instead of deprecated Drools Rule Templates (DRT)6:18
Declare intermediate types in DRL5:46
How to declare enumerations in and read back objects of type declared in DRL7:44
Create and insert objects into the session that have type declared in DRL3:23
Rule templates recap1:27

Requirements

You should have basic understanding of Java programming

Description

We learn Apache Drools DSL (Drools programming language) and go over the most common DSL constructs. We move in small steps and gradually introduce new concepts, so it is easier to follow even for a beginner.

This way we cover the most common Drools topics like:

what is a rule engine
what is the difference between a method and a rule
why one would use a rule engine instead of writing regular Java code
understanding of the when/then clauses
understanding in which order the rules fire and when the order is not known
how to control the execution using activation groups, agenda groups and salience
declaring variables in DRL
difference between stateless and stateful sessions
inserting facts and modifying existing objects in the session
cross products (similar to SQL join)
exists, forall and collect
using spreadsheet decision tables to create Drools rules
using templates for creating rules and feeding data into them from spreadsheets and other tabular data sources
complex event processing (CEP) in Drools
- difference between fact and event
- declaring facts and events in Java and inside DRL code
- different rule execution modes (active/passive, cloud/stream, sequential)
- time and length-based sliding windows
- entry-points
- global variables
- timers
how Apache Drools' internal algorithm Phreak works

This course comes with two Java projects containing all the code we worked with during the course. The first project includes all the code examples in traditional Drools syntax and a second copy of all the rules in the new Drools OOPath syntax (introduced by Drools 8). The first project has been upgraded to run using Drools 10.

You are encouraged to check out and run the code yourself to better understand and experiment with changes.

There are instructions on running the code in IntelliJ, Eclipse, and VS Code.

After completing this course, you will better understand which kinds of problems could be solved with Drools and how to write the most common business rules in Drools DSL.

Who this course is for:

Developers and system architects who need to understand what a rule engine is and which type of problems can be solved with it
Anyone who needs to write rules in Drools DSL programming language
Developers and system architects needing more info about adding Drools rule engine to their project
Anyone who is considering using Drools for writing rules or processing stream of events

Master Drools Programming - Learn How to Write Drools Rules

What you'll learn

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Course content

1. Introduction4 lectures • 23min

2. Example Code and Running it Locally5 lectures • 20min

3. Stateless Sessions8 lectures • 31min

4. Stateful Sessions4 lectures • 13min

5. Cross Products - Drools Version of SQL JOIN6 lectures • 25min

Insert new facts and determine the execution order10 lectures • 41min

Insert a fact logically and check that the fact does not exist7 lectures • 27min

8. Exists and Forall Conditional Elements7 lectures • 23min

9. Spreadsheet Decision Tables17 lectures • 1hr 51min

Rule templates and creating rules dynamically8 lectures • 51min

Requirements

Description

Who this course is for: