These days rule engines are often overlooked, possibly because people think that they are only useful inside heavyweight enterprise software products. However, this is not necessarily true. Simply put, a rule engine is just a piece of software that allows you to separate domain and business-specific constraints from the main application flow. I am the project lead of Drools, the rule engine of Red Hat, and my target was to modernize my project and make it ready to be used in serverless environments. In this talk I will explore and make sense of technologies like GraalVM and Quarkus. I will show, with practical use cases taken from my experience with this migration, what is necessary to change in a code base — making extensive use of reflection, dynamic class loading, and other Java sorceries — to make it compatible with those technologies, and demonstrate how this is allowing us to make Drools part of the cloud and serverless revolution.

1. How and why I turned my old
Java projects into a first-class
serverless component
by Mario Fusco
Red Hat – Principal Software Engineer
@mariofusco

2. ● A cloud-native development, deployment and execution platform for
business automation:
○ Rules and Decisions (Drools)
○ Processes and Cases (jBPM)
● ... under the covers
○ the backbone is code generation based on business assets
○ executable model for the process/rule/decision definitions
○ type safe data model that encapsulates variables
○ REST api for each public business process/decision/rule
Introducing

3. Demo
Kogito + Quarkus

4. Cool, but ... how did we get there?
A minimal agenda
⮚GraalVM features and limitations
⮚How (and why) we made Drools
natively compilable on GraalVM
⮚How we integrated Kogito with
Quarkus: creating a Quarkus extension
⮚Enabling hot reload of rules, decision
tables and processes
⮚One last demo

5. What is
used by Quarkus
➢
A polyglot VM with cross-language JIT
supporting
●
Java Bytecode and JVM languages
●
Interop with different languages
●
Dynamic languages through Truffle API
➢
Cross-language interop out of the box
●
Simple AST-based interpreter
●
JIT across language boundaries
➢
Support for native binary compilation
(SubstrateVM)
●
faster boot-up
●
lower memory footprint

6. AoT compilation with GraalVM
➢
Static analysis
➢
Closed world assumption
➢
Dead code elimination:
classes, fields, methods, branches

7. AoT compilation with GraalVM
➢
Static analysis
➢
Closed world assumption
➢
Dead code elimination:
classes, fields, methods, branches
🚀 Fast process start
🔬 Less memory
💾 Small size on disk

8. GraalVM Limitations
Dynaminc Classloading
Deloying jars, wars, etc. at runtime impossible
public class InternalClassLoader extends ClassLoader {
public Class<?> defineClass( String name, byte[] bytecode ) {
return defineClass( name, bytecode, 0, bytecode.length );
}
}

9. GraalVM Limitations
Dynaminc Classloading
Deloying jars, wars, etc. at runtime impossible
public class InternalClassLoader extends ClassLoader {
public Class<?> defineClass( String name, byte[] bytecode ) {
return defineClass( name, bytecode, 0, bytecode.length );
}
}

10. GraalVM Limitations
Dynaminc Classloading
Deloying jars, wars, etc. at runtime impossible
public class InternalClassLoader extends ClassLoader {
public Class<?> defineClass( String name, byte[] bytecode ) {
return defineClass( name, bytecode, 0, bytecode.length );
}
}
JVMTI, JMX + other
native VM interfaces
No agents → No JRebel, Byteman, profilers, tracers
Miscellaneous
➢
Security Manager
➢ finalize() (depreceated anyway)
➢ InvokeDynamic and MethodHandle

11. GraalVM Limitations
Dynaminc Classloading
Deloying jars, wars, etc. at runtime impossible
public class InternalClassLoader extends ClassLoader {
public Class<?> defineClass( String name, byte[] bytecode ) {
return defineClass( name, bytecode, 0, bytecode.length );
}
}
JVMTI, JMX + other
native VM interfaces
No agents → No JRebel, Byteman, profilers, tracers
Miscellaneous
➢
Security Manager
➢ finalize() (depreceated anyway)
➢ InvokeDynamic and MethodHandle

12. GraalVM Limitations
Dynaminc Classloading
Deloying jars, wars, etc. at runtime impossible
public class InternalClassLoader extends ClassLoader {
public Class<?> defineClass( String name, byte[] bytecode ) {
return defineClass( name, bytecode, 0, bytecode.length );
}
}
JVMTI, JMX + other
native VM interfaces
No agents → No JRebel, Byteman, profilers, tracers
Miscellaneous
➢
Security Manager
➢ finalize() (depreceated anyway)
➢ InvokeDynamic and MethodHandle
Reflection
Requires registration (closed world assumption)

13. GraalVM Limitations
Dynaminc Classloading
Deloying jars, wars, etc. at runtime impossible
public class InternalClassLoader extends ClassLoader {
public Class<?> defineClass( String name, byte[] bytecode ) {
return defineClass( name, bytecode, 0, bytecode.length );
}
}
JVMTI, JMX + other
native VM interfaces
No agents → No JRebel, Byteman, profilers, tracers
Miscellaneous
➢
Security Manager
➢ finalize() (depreceated anyway)
➢ InvokeDynamic and MethodHandle
[
{
"name" : "org.domain.model.Person",
"allPublicConstructors" : true,
"allPublicMethods" : true
}
]
Reflection
Requires registration (closed world assumption)
-H:ReflectionConfigurationFiles=src/main/resources/reflection.json

14. Drools on GraalVM - Executable Model
rule "Older than Mark" when
$p1: Person( name == "Mark" )
$p2: Person( name != "Mark", age > $p1.age )
then
System.out.println( $p1.getName() +
" is older than " + $p2.getName() );
end
Variable<Person> markV = declarationOf( Person.class );
Variable<Person> olderV = declarationOf( Person.class );
Rule rule = rule( "Older than Mark" )
.build(
pattern(markV)
.expr("exprA", p -> p.getName().equals( "Mark" ),
alphaIndexedBy( String.class, ConstraintType.EQUAL, 1, p -> p.getName(), "Mark" ),
reactOn( "name", "age" )),
pattern(olderV)
.expr("exprB", p -> !p.getName().equals("Mark"),
alphaIndexedBy( String.class, ConstraintType.NOT_EQUAL, 1, p -> p.getName(), "Mark" ),
reactOn( "name" ))
.expr("exprC", markV, (p1, p2) -> p1.getAge() > p2.getAge(),
betaIndexedBy( int.class, ConstraintType.GREATER_THAN, 0, p -> p.getAge(), p -> p.getAge() ),
reactOn( "age" )),
on(olderV, markV).execute((p1, p2) -> System.out.println( p1.getName() + " is older than " + p2.getName() ))
)

15. Drools on GraalVM - Executable Model
rule "Older than Mark" when
$p1: Person( name == "Mark" )
$p2: Person( name != "Mark", age > $p1.age )
then
System.out.println( $p1.getName() +
" is older than " + $p2.getName() );
end
Variable<Person> markV = declarationOf( Person.class );
Variable<Person> olderV = declarationOf( Person.class );
Rule rule = rule( "Older than Mark" )
.build(
pattern(markV)
.expr("exprA", p -> p.getName().equals( "Mark" ),
alphaIndexedBy( String.class, ConstraintType.EQUAL, 1, p -> p.getName(), "Mark" ),
reactOn( "name", "age" )),
pattern(olderV)
.expr("exprB", p -> !p.getName().equals("Mark"),
alphaIndexedBy( String.class, ConstraintType.NOT_EQUAL, 1, p -> p.getName(), "Mark" ),
reactOn( "name" ))
.expr("exprC", markV, (p1, p2) -> p1.getAge() > p2.getAge(),
betaIndexedBy( int.class, ConstraintType.GREATER_THAN, 0, p -> p.getAge(), p -> p.getAge() ),
reactOn( "age" )),
on(olderV, markV).execute((p1, p2) -> System.out.println( p1.getName() + " is older than " + p2.getName() ))
)

16. Drools on GraalVM - Executable Model
rule "Older than Mark" when
$p1: Person( name == "Mark" )
$p2: Person( name != "Mark", age > $p1.age )
then
System.out.println( $p1.getName() +
" is older than " + $p2.getName() );
end
Variable<Person> markV = declarationOf( Person.class );
Variable<Person> olderV = declarationOf( Person.class );
Rule rule = rule( "Older than Mark" )
.build(
pattern(markV)
.expr("exprA", p -> p.getName().equals( "Mark" ),
alphaIndexedBy( String.class, ConstraintType.EQUAL, 1, p -> p.getName(), "Mark" ),
reactOn( "name", "age" )),
pattern(olderV)
.expr("exprB", p -> !p.getName().equals("Mark"),
alphaIndexedBy( String.class, ConstraintType.NOT_EQUAL, 1, p -> p.getName(), "Mark" ),
reactOn( "name" ))
.expr("exprC", markV, (p1, p2) -> p1.getAge() > p2.getAge(),
betaIndexedBy( int.class, ConstraintType.GREATER_THAN, 0, p -> p.getAge(), p -> p.getAge() ),
reactOn( "age" )),
on(olderV, markV).execute((p1, p2) -> System.out.println( p1.getName() + " is older than " + p2.getName() ))
)
Executable
model
Indexes and
reactivity
explicitly defined

17. Executable Model at a glance
➢
A pure Java DSL for Drools rules authoring
➢
A pure Java canonical representation of a rule base
➢
Automatically generated by Maven plugin or
Quarkus extension
●
Can be embedded in jar
●
Faster boot
➢
Improve Backward/Forward compatibility
➢
Allow for faster prototyping and experimentation of
new features
➢
Prerequisite to make Drools natively compilable on
GraalVM

18. public class InternalClassLoader extends ClassLoader {
public Class<?> defineClass( String name, byte[] bytecode ) {
throw new UnsupportedOperationException();
}
}
Drools on GraalVM – other refactors
Dynamic class definition
is no longer necessary

19. public class InternalClassLoader extends ClassLoader {
public Class<?> defineClass( String name, byte[] bytecode ) {
throw new UnsupportedOperationException();
}
}
Drools on GraalVM – other refactors
Dynamic class definition
is no longer necessary
<?xml version="1.0" encoding="UTF-8"?>
<kmodule xmlns="http://jboss.org/kie/6.0.0/kmodule">
<kbase name="simpleKB"
packages="org.drools.simple.project">
<ksession name="simpleKS" default="true"/>
</kbase>
</kmodule>
var m = KieServices.get().newKieModuleModel();
var kb = m.newKieBaseModel("simpleKB");
kb.setEventProcessingMode(CLOUD);
kb.addPackage("org.drools.simple.project");
var ks = kb.newKieSessionModel("simpleKS");
ks.setDefault(true);
ks.setType(STATEFUL);
ks.setClockType(ClockTypeOption.get("realtime"));

20. public class InternalClassLoader extends ClassLoader {
public Class<?> defineClass( String name, byte[] bytecode ) {
throw new UnsupportedOperationException();
}
}
Drools on GraalVM – other refactors
Dynamic class definition
is no longer necessary
<?xml version="1.0" encoding="UTF-8"?>
<kmodule xmlns="http://jboss.org/kie/6.0.0/kmodule">
<kbase name="simpleKB"
packages="org.drools.simple.project">
<ksession name="simpleKS" default="true"/>
</kbase>
</kmodule>
var m = KieServices.get().newKieModuleModel();
var kb = m.newKieBaseModel("simpleKB");
kb.setEventProcessingMode(CLOUD);
kb.addPackage("org.drools.simple.project");
var ks = kb.newKieSessionModel("simpleKS");
ks.setDefault(true);
ks.setType(STATEFUL);
ks.setClockType(ClockTypeOption.get("realtime"));
org.kie.api.io.KieResources =
org.drools.core.io.impl.ResourceFactoryServiceImpl
org.kie.api.marshalling.KieMarshallers =
org.drools.core.marshalling.MarshallerProviderImpl
org.kie.api.concurrent.KieExecutors =
org.drools.core.concurrent.ExecutorProviderImpl
Map<Class<?>, Object> serviceMap = new HashMap<>();
void wireServices() {
serviceMap.put( ServiceInterface.class,
Class.forName("org.drools.ServiceImpl")
.newInstance());
// … more services here
}

21. JVM vs.
Native

22. Introducing
➢
A Framework for writing (fast and
lightweight) Java applications

23. Introducing
➢
A Framework for writing (fast and
lightweight) Java applications
➢
(Optionally) allowing generation
of native executable via GraalVM
*.class
QUARKUS
optimized jar
native
executable
JVM
Maven/Gradle plugin

24. Introducing
➢
A Framework for writing (fast and
lightweight) Java applications
➢
(Optionally) allowing generation
of native executable via GraalVM
➢
Based on existing standard
●
Servlet
●
JAX-RS
●
JPA, JDBC
●
CDI
●
Bean Validation
●
Transactions
●
Logging
●
Microprofile
*.class
QUARKUS
optimized jar
native
executable
JVM
Maven/Gradle plugin

25. Introducing
➢
A Framework for writing (fast and
lightweight) Java applications
➢
(Optionally) allowing generation
of native executable via GraalVM
➢
Based on existing standard
●
Servlet
●
JAX-RS
●
JPA, JDBC
●
CDI
●
Bean Validation
●
Transactions
●
Logging
●
Microprofile
➢
Out-of-the-box integration with
libraries that you already know
*.class
QUARKUS
optimized jar
native
executable
JVM
Maven/Gradle plugin

26. Compile generate
Java sources in
memory
Integrating Quarkus and Kogito
Writing a Quarkus extension
public class KogitoAssetProcessor {
@BuildStep(providesCapabilities = "io.quarkus.kogito")
public void generateModel( ArchiveRootBuildItem root,
BuildProducer<GeneratedBeanBuildItem> generatedBeans,
LaunchModeBuildItem launchMode) throws IOException {
LaunchMode launchMode = launchModeItem.getLaunchMode();
if (hotReload(launchMode)) {
return;
}
ApplicationGenerator appGen = createApplicationGenerator(root, launchMode);
Collection<GeneratedFile> generatedFiles = appGen.generate();
if (!generatedFiles.isEmpty()) {
MemoryFileSystem trgMfs = new MemoryFileSystem();
CompilationResult result = compile( root, trgMfs, generatedFiles,
generatedBeans, launchMode );
register( trgMfs, generatedBeans, launchMode, result );
}
}
}
Avoid recompiling
everything during
an hot reload
Generate
executable model
source files
Register generated
classes into
Quarkus runtime

27. Kogito hot reload
public class KogitoCompilationProvider extends JavaCompilationProvider {
@Override
public final void compile(Set<File> filesToCompile, Context context) {
File outputDirectory = context.getOutputDirectory();
try {
ApplicationGenerator appGen = new ApplicationGenerator( appPackageName,
outputDirectory );
Generator generator = addGenerator(appGen, filesToCompile, context);
Collection<GeneratedFile> generatedFiles = generator.generate();
HashSet<File> generatedSourceFiles = new HashSet<>();
for (GeneratedFile file : generatedFiles) {
Path path = pathOf(outputDirectory.getPath(), file.relativePath());
Files.write(path, file.contents());
generatedSourceFiles.add(path.toFile());
}
super.compile(generatedSourceFiles, context);
} catch (IOException e) {
throw new KogitoCompilerException(e);
}
}
}
Write regenerated
source in the file
system
Extends Java hot
reload mechanism
provided by Quarkus
Regenerate executable
model only for changed
sources
Pass the list of
generated sources to
super in order to
recompile them

28. A simple Quarkus-based
REST endpoint using Kogito
@Path("/candrink/{name}/{age}")
public class CanDrinkResource {
@Inject @Named("canDrinkKS")
RuleUnit<SessionMemory> ruleUnit;
@GET
@Produces(MediaType.TEXT_PLAIN)
public String canDrink( @PathParam("name") String name, @PathParam("age") int age ) {
SessionMemory memory = new SessionMemory();
Result result = new Result();
memory.add(result);
memory.add(new Person( name, age ));
ruleUnit.evaluate(memory);
return result.toString();
}
}

29. What’s next?
Don’t miss Maciej Swiderski’s DevNationLive talk on the 5th
of September:
Event-driven business automation powered by cloud native Java
➢
Rule bases modularization via
Rule Units
➢
Rule Units orchestration through
jBPM workflows
➢
Seamless integration with Camel
routes, Kafka streams, ...
➢
Automatic REST endpoint
generation returning result of DRL
queries

30. Mario Fusco
Red Hat – Principal Software Engineer
mario.fusco@gmail.com
twitter: @mariofusco
Q A
Thanks ... Questions?