Got RuntimeException：Unknown resource type: ResourceType = 'jBPM BPMN2 Language' when initiating a kie session - drools

Question

I have created a business process and build it as a jar in Kie Workbench (version 7.16.0.Final).
When trying to execute the process I got the Runtime exception.
2019-01-20 21:35:57.092 [http-nio-9043-exec-8] ERROR o.a.c.c.C.[.[.[.[dispatcherServlet] - Servlet.service() for servlet [dispatcherServlet] in context with path [] threw exception [Request processing failed; nested exception is java.lang.RuntimeException: Unknown resource type: ResourceType = 'jBPM BPMN2 Language'] with root cause
java.lang.RuntimeException: Unknown resource type: ResourceType = 'jBPM BPMN2 Language'
at org.kie.internal.services.KieAssemblersImpl.addResource(KieAssemblersImpl.java:51)
at org.drools.compiler.builder.impl.KnowledgeBuilderImpl.addPackageForExternalType(KnowledgeBuilderImpl.java:778)
at org.drools.compiler.builder.impl.KnowledgeBuilderImpl.addKnowledgeResource(KnowledgeBuilderImpl.java:763)
at org.drools.compiler.builder.impl.CompositeKnowledgeBuilderImpl$ResourceBuilder.lambda$static$6(CompositeKnowledgeBuilderImpl.java:307)
at org.drools.compiler.builder.impl.CompositeKnowledgeBuilderImpl.buildResourceType(CompositeKnowledgeBuilderImpl.java:141)
at org.drools.compiler.builder.impl.CompositeKnowledgeBuilderImpl.buildProcesses(CompositeKnowledgeBuilderImpl.java:121)
at org.drools.compiler.builder.impl.CompositeKnowledgeBuilderImpl.build(CompositeKnowledgeBuilderImpl.java:112)
at org.drools.compiler.builder.impl.CompositeKnowledgeBuilderImpl.build(CompositeKnowledgeBuilderImpl.java:100)
at org.drools.compiler.kie.builder.impl.AbstractKieProject.buildKnowledgePackages(AbstractKieProject.java:251)
at org.drools.compiler.kie.builder.impl.AbstractKieModule.buildKnowledgePackages(AbstractKieModule.java:201)
at org.drools.compiler.kie.builder.impl.AbstractKieModule.createKieBase(AbstractKieModule.java:214)
at org.drools.compiler.kie.builder.impl.KieContainerImpl.createKieBase(KieContainerImpl.java:406)
at org.drools.compiler.kie.builder.impl.KieContainerImpl.getKieBase(KieContainerImpl.java:374)
at org.drools.compiler.kie.builder.impl.KieContainerImpl.getKieBaseFromKieSessionModel(KieContainerImpl.java:575)
at org.drools.compiler.kie.builder.impl.KieContainerImpl.newKieSession(KieContainerImpl.java:551)
at org.drools.compiler.kie.builder.impl.KieContainerImpl.newKieSession(KieContainerImpl.java:521)

Answer 1

I faced this same issue (although in KIE/Drools 7.17.0.Final) and the problem was a missing dependency. In my case I had Drools/KIE/JBPM as a JBoss module and didn't have all required JARs declared in module.xml.
What I did to fix it was to add the following two JARs to module.xml (and of course, put the JARs into the module's main folder):
jbpm-bpmn2-7.17.0.Final.jar
jbpm-flow-builder-7.17.0.Final.jar
You can find these JARs under Drools and jBPM tools distribution.

Answer 2

When using as runtime version one of the latest:
<runtime.version>7.42.0.Final</runtime.version>
Then, it's enough to have the following set of libraries (which are automatically added if you create a Drools project with Eclipse+Drools plugin):
<dependency>
<groupId>org.kie</groupId>
<artifactId>kie-api</artifactId>
</dependency>
<dependency>
<groupId>org.drools</groupId>
<artifactId>drools-core</artifactId>
</dependency>
<dependency>
<groupId>org.drools</groupId>
<artifactId>drools-decisiontables</artifactId>
</dependency>
<dependency>
<groupId>org.jbpm</groupId>
<artifactId>jbpm-test</artifactId>
</dependency>
There's a sample demo project here: Using Drools Rules with jBPM