Book Image

Mastering JBoss Drools 6

By : Mariano De Maio, Mauricio Salatino, Esteban Aliverti
Book Image

Mastering JBoss Drools 6

By: Mariano De Maio, Mauricio Salatino, Esteban Aliverti

Overview of this book

Mastering JBoss Drools 6 will provide you with the knowledge to develop applications involving complex scenarios. You will learn how to use KIE modules to create and execute Business Rules, and how the PHREAK algorithm internally works to drive the Rule Engine decisions. This book will also cover the relationship between Drools and jBPM, which allows you to enrich your applications by using Business Processes. You will be briefly introduced to the concept of complex event processing (Drools CEP) where you will learn how to aggregate and correlate your data based on temporal conditions. You will also learn how to define rules using domain-specific languages, such as spreadsheets, database entries, PMML, and more. Towards the end, this book will take you through the integration of Drools with the Spring and Camel frameworks for more complex applications.

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Mastering JBoss Drools 6
Mariano De Maio | Mauricio Salatino | Esteban Aliverti
Mar, 2016 | 330 pages
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Table of Contents (18 chapters)
Mastering JBoss Drools 6
Mastering JBoss Drools 6
Credits
Credits
About the Authors
About the Authors
About the Reviewer
About the Reviewer
www.PacktPub.com
www.PacktPub.com
Preface
Preface
Free Chapter
1
Rules Declarative Nature
Rules Declarative Nature
What are rules?
Why do we use rules?
When should we use rules?
When not to use a rule engine
Summary
2
Writing and Executing Rules
Writing and Executing Rules
Setting up our environment
Creating our first Drools project
Writing and executing our first rule
The Rule language
Organizing our projects
Summary
3
Drools Runtime
Drools Runtime
Understanding the Drools runtime instances
KieModule configurations (KieBases, KieSessions & StatelessKieSessions)
KieScanner
Summary
4
Improving Our Rule Syntax
Improving Our Rule Syntax
Adding external interactions with global variables
Modifying the data in the working memory
Rule attributes
Controlling loops in rules
Special Drools operations
Working memory breakdown: the from clause
Drools syntactic sugar
Decorating our objects in memory
Logical insertion of elements
Rule inheritance
Summary
5
Understanding KIE Sessions
Understanding KIE Sessions
Stateless and stateful Kie Sessions
Kie runtime components
Kie Base components
Summary
6
Complex Event Processing
Complex Event Processing
What is complex event processing?
Declaring CEP-based Rules
Event-driven architecture
Running CEP-based Scenarios
Drools CEP limitations
Summary
7
Human-Readable Rules
Human-Readable Rules
Domain Specific Languages
Decision tables
Rule templates
PMML
Summary
8
Rules' Testing and Troubleshooting
Rules' Testing and Troubleshooting
Create loosely coupled DRLs
Prefer KieHelper over a KieContainer classpath
Benefits of using globals
Debugging the left-hand side of a rule
Debugging the right-hand side of a rule
Reporting a bug in Drools
Summary
9
Introduction to PHREAK
Introduction to PHREAK
Introducing PHREAK
Special nodes in the network
Queries and backward-chaining
PHREAK improvements over RETE
Phreak Inspector
Summary
10
Integrating Rules and Processes
Integrating Rules and Processes
jBPM – the process engine
Simple business process example
Drools and jBPM: integration patterns
Persistence and transactions
Summary
11
Integrating Drools with our Apps
Integrating Drools with our Apps
Architecture considerations
Integrating with the rest of an application
CDI integration
Spring integration
Camel integration
Kie Execution Server
Kie Workbench
Drools and beyond: extending our functionality
Summary
Index
Index

Debugging the right-hand side of a rule

As we already know, the right-hand side of a rule in Drools may contain a combination of the following elements:

  • Java sentences: Any regular Java sentence that is allowed in a Java method can also be used on the right-hand side of a rule in Drools.

  • MVEL expressions: If the dialect of the rule is set to mvel, MVEL expressions are enabled on the right-hand side of the rule in Drools.

  • Predefined variables and methods: Variables such as drools and kcontext and methods such as insert, update, and delete are also allowed. The special modify(){} structure could also be used on the right-hand side of the rule in Drools.

In the previous section, we introduced the notion of how, when compiled, the left-hand side of all the rules in a KIE Base is converted into a network of nodes. For the right-hand side of the rules, the situation is different. When a KIE Base is compiled, the right-hand side of each of the rules that it contains is converted into a Java class....

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