Master Drools Programming - Learn How to Write Drools Rules

Learn to check out and run the Drools example code with IntelliJ IDEA Community Edition by cloning from GitHub, importing as a Maven project, and configuring Java 8.

Explore stateless sessions in Drools to validate passports, assess visa eligibility, and apply rules for travel insurance calculations, expenses approvals, and email filtering.

Define two stateless session rules to validate passports, matching valid passports and invalid ones (expired or with no unused visa pages) using a Drools container in step one.

Split a single multi-purpose Drools rule into two focused rules, one matching expired passports and another matching passports with zero unused visa pages, and compare the changes in step two.

Bind a variable in step three of stateless Drools sessions to show passport ownership. Print the owner and visa status using pattern binding and getters like getName and getUnusedVisaPages.

Step four demonstrates managing a Drools session, using a bound variable and a new enum validation to set passport results, then reading states back in Java code.

Rewrite the rule to avoid repetition in steps five and six, treating passports without validation info as okay while rules mark invalid ones, and note stateless sessions can't reflect changes.

Explore stateless sessions and use cases—validation, calculation, routing, and filtering—and how to declare statelessness in XML, while keeping rules short, using dollar-prefixed variables, and noting that state changes aren’t propagated.

Explore stateful vs stateless Drools sessions, inserting and modifying passport facts, firing rules, and ensuring order-independent results while avoiding memory leaks by disposing sessions.

Use stateful sessions when you rely on inference, letting rule set information consumed by another, use modify to update objects so affected rules rerun, dispose at end to prevent leaks.

Explore how Drools rules join passports with visa applications to validate entries, using a stateful session to insert visa applications and modify objects to reflect validation results.

In step two of Drools programming, learn to enforce passport validity six months after visit end by adding a cross-product rule that flags visa applications and marks validation failed.

Add new facts with Drools, issue visas when validation passes, and learn to control rule execution order using salience or agenda groups.

Create a new visa fact when a visa application passes validation, insert it into the session during rule execution, and later read all visas issued by the rules.

Master Drools rule execution by controlling order with salience, and learn how conflicts arise when multiple rules could fire and how high salience fires first.

Learn to control drools execution with agenda groups instead of salience, organizing rules into invalid passport, valid passport, invalid application, and valid application groups, using a stack and debug listener.

Use three agenda groups: validate passport, validate application, and issuing visa, and apply salience within the groups to prioritize failed validations over passes.

Explore activation groups in Drools, see how only one rule fires per group, and learn how agenda groups, salience, and date-based state changes shape visa validation.

Explore logical insertion of facts in Drools, using insert logical and not to manage fact existence, bind object existence to the when clause, and add new facts to reduce rules.

demonstrates insert logical in drools by inserting visas, tracking updates and deletions with event listeners; shows how changing the when clause can delete previously inserted facts and invalidate visa applications.

In this step, rewrite Drools rules to use fact objects instead of modifying passports and visa applications, inserting valid or invalid fact objects as session stickers.

Eliminate positive cases by focusing on negative ones, rewrite the visa rule with red stickers, and automatically remove invalid visas, reducing the rule set to four.

Design Drools rules with fact objects, manage session facts, and track insertions, updates, and removals using event listeners for debugging, ensuring extensible, well-structured rule logic.

Rewrite visa application logic to support family visa applications by validating multiple passports, issuing visas per passport, and retracting them when an invalid passport is found.

Rewrite the rule to fire only once using the exists keyword. This ensures a family visa application is invalidated if at least one invalid passport exists, without duplicating facts.

Learn to use for all in Drools to extract a specific value from a group, such as selecting the oldest member as group leader when all are under 18.

Rewrite a complex drools rule to a single for all expression, ensuring the group leader and all members are under 18, then confirm all are at least ten.

Learn to work with groups of facts in Drools, using exist to confirm at least one fact and for all to validate expressions or find the lowest or highest value.

Learn how spreadsheet decision tables convert independent conditions into drools rules. Use a family visa fee example to map urgent and person count to a DRL action.

Open the spreadsheet decision table, view the three conditional columns and one action, then convert it to a drl file to drive rule execution that prints fees 300, 100, 140.

Define multiple action columns in a spreadsheet to link visa applications with fees, add a visa fee domain object and insert action, and retrieve results from the rule session.

Demonstrates using formulas in a spreadsheet decision table for Drools, converting Java code into rules, handling quotes, and debugging generated rules.

Set a custom drl rule name and add a comment by using the name and description columns in the rule table, showing how rules are generated from rows.

Learn to fit multiple rule tables in a single spreadsheet by structuring the rule set package and imports, with each table independent and separated by a blank line.

Demonstrates how to use Drools with multiple rule tables in a spreadsheet to generate visa fees from passport data, with parameter substitution, and notes that the first sheet is used.

Join multiple fact objects in a spreadsheet decision table by linking passport and visa application with the passport number to calculate the urgent fee in a Drools rules session.

In step seven of spreadsheet decision tables, the for all construct repeats a condition across a list, enabling not-in checks and guiding DRL generation.

Apply a not clause to a where condition in a spreadsheet decision table without a pattern, checking that no visa fee object with a given application id exists.

Sequential true in rule sets adds unique salience to each rule, overriding the priority column, and demonstrates using a sequential max priority to control firing order.

Explore activation groups in spreadsheet decision tables and how they limit rule firing. See how join columns, params, and variables merge data, with salience guiding sequential execution.

Learn to use custom labels in spreadsheet decision tables to drive Drools rules, using conditions and actions starting with C and A to manage fees and discounts.

Explore how to use Drools rule templates (drt) to generate visa decision rules from tabular data, including handling age gaps, unemployment, bookings, and randomized interview thresholds.

Fetches placeholder values from a tabular data source to populate Drools rule templates, loads rules from a string into an in-memory file system, and executes them to determine visa outcomes.

Declare an intermediate type in DRL to model a risk factor with visa application id and risk, insert it, and count risk factors to decide a visa verdict.

Declare and use enumerations in Drools DRL, read back risk factor objects as enums, and handle intermediate facts with Java integration for debugging and JSON conversion.

Recap rule templates and their placeholders; explore separating data from rules using XLS or databases, noting deprecation of templates and alternative templating, including Freemarker and direct string composition.