Chapter 12. CDI

CDI, Contexts and Dependency Injection, is Java specification that provides declarative controls and strucutres to an application. KIE can use it to automatically instantiate and bind things, without the need to use the programmatic API.

12.2. Annotations

@KContainer, @KBase and @KSession all support an optional 'name' attribute. CDI typically does "getOrCreate" when it injects, all injections receive the same instance for the same set of annotations. the 'name' annotation forces a unique instance for each name, although all instance for that name will be identity equals.

12.2.1. @KReleaseId

Used to bind an instance to a specific version of a KieModule. If kie-ci is on the classpath this will resolve dependencies automatically, downloading from remote repositories.

12.2.2. @KContainer

@KContainer is optional as it can be detected and added by the use of @Inject and variable type inferrence.

Figure 12.1. Injects Classpath KieContainer

@Inject
private KieContainer kContainer;

Figure 12.2. Injects KieContainer for Dynamic KieModule

@Inject
@KReleaseId(groupId = "jar1", artifactId = "art1", version = "1.1")
private KieContainer kContainer;

Figure 12.3. Injects named KieContainer for Dynamic KieModule

@Inject
@KContainer(name = "kc1")
@KReleaseId(groupId = "jar1", artifactId = "art1", version = "1.1")
private KieContainer kContainer;

12.2.3. @KBase

@KBase is optional as it can be detected and added by the use of @Inject and variable type inference.

The default argument, if given, maps to the value attribute and specifies the name of the KieBase from the kmodule.xml file.

Figure 12.4. Injects the Default KieBase from the Classpath KieContainer

@Inject
private KieBase kbase;

Figure 12.5. Injects the Default KieBase from a Dynamic KieModule

@Inject
@KReleaseId( groupId = "jar1", artifactId = "art1", version = "1.0")   
private KieBase kbase;

Figure 12.6. Side by side version loading for 'jar1.KBase1' KieBase

@Inject
@KBase("kbase1")
@KReleaseId( groupId = "jar1", artifactId = "art1", version = "1.0")
private KieBase kbase1v10;

@Inject
@KBase("kbase1") 
@KReleaseId( groupId = "jar1", artifactId = "art1", version = "1.1")
private KieBase kbase1v10;

Figure 12.7. Use 'name' attribute to force new Instance for 'jar1.KBase1' KieBase

@Inject
@KSession(value="kbase1", name="kb1")
@KReleaseId( groupId = "jar1", artifactId = "art1", version = "1.0")
private KieBase kbase1kb1;

@Inject  
@KSession(value="kbase1", name="kb2")    
@KReleaseId( groupId = "jar1", artifactId = "art1", version = "1.0")
private KieBase kbase1kb2;

12.2.4. @KSession for KieSession

@KSession is optional as it can be detected and added by the use of @Inject and variable type inference.

The default argument, if given, maps to the value attribute and specifies the name of the KieSession from the kmodule.xml file

Figure 12.8. Injects the Default KieSession from the Classpath KieContainer

@Inject
private KieSession ksession;

Figure 12.9. Injects the Default KieSession from a Dynamic KieModule

@Inject
@KReleaseId( groupId = "jar1", artifactId = "art1", version = "1.0")   
private KieSession ksession;

Figure 12.10. Side by side version loading for 'jar1.KBase1' KieBase

@Inject
@KSession("ksession1") 
@KReleaseId( groupId = "jar1", artifactId = "art1", version = "1.0")
private KieSession ksessionv10;

@Inject
@KSession("ksession1") 
@KReleaseId( groupId = "jar1", artifactId = "art1", version = "1.1")
private KieSession ksessionv11;

Figure 12.11. Use 'name' attribute to force new Instance for 'jar1.KBase1' KieSession

@Inject
@KSession(value="ksession1", name="ks1")
@KReleaseId( groupId = "jar1", artifactId = "art1", version = "1.0")
private KieSession ksession1ks1

@Inject  
@KSession(value="ksession1", name="ks2")    
@KReleaseId( groupId = "jar1", artifactId = "art1", version = "1.0")
private KieSession ksession1ks2

12.2.5. @KSession for StatelessKieSession

@KSession is optional as it can be detected and added by the use of @Inject and variable type inference.

The default argument, if given, maps to the value attribute and specifies the name of the KieSession from the kmodule.xml file.

Figure 12.12. Injects the Default StatelessKieSession from the Classpath KieContainer

@Inject
private StatelessKieSession ksession;

Figure 12.13. Injects the Default StatelessKieSession from a Dynamic KieModule

@Inject
@KReleaseId( groupId = "jar1", artifactId = "art1", version = "1.0")   
private StatelessKieSession ksession;

Figure 12.14. Side by side version loading for 'jar1.KBase1' KieBase

@Inject
@KSession("ksession1") 
@KReleaseId( groupId = "jar1", rtifactId = "art1", version = "1.0")
private StatelessKieSession ksessionv10;

@Inject
@KSession("ksession1") 
@KReleaseId( groupId = "jar1", rtifactId = "art1", version = "1.1")
private StatelessKieSession ksessionv11;

Figure 12.15. Use 'name' attribute to force new Instance for 'jar1.KBase1' StatelessKieSession

@Inject
@KSession(value="ksession1", name="ks1")
@KReleaseId( groupId = "jar1", artifactId = "art1", version = "1.0")
private StatelessKieSession ksession1ks1

@Inject  
@KSession(value="ksession1", name="ks2")    
@KReleaseId( groupId = "jar1", artifactId = "art1", version = "1.0")
private StatelessKieSession ksession1ks2

12.3. API Example Comparison

CDI can inject instances into fields, or even pass them as arguments. In this example field injection is used.

Figure 12.16. CDI example for a named KieSession

@Inject
@KSession("ksession1")
KieSession kSession;

public void go(PrintStream out) {
    kSession.setGlobal("out", out);
    kSession.insert(new Message("Dave", "Hello, HAL. Do you read me, HAL?"));
    kSession.fireAllRules();
}

This is less code and more declarative than the API approach.

Figure 12.17. API equivalent example for a named KieSession

public void go(PrintStream out) {
    KieServices ks = KieServices.Factory.get();
    KieContainer kContainer = ks.getKieClasspathContainer();

    KieSession kSession = kContainer.newKieSession("ksession1");
    kSession.setGlobal("out", out);
    kSession.insert(new Message("Dave", "Hello, HAL. Do you read me, HAL?"));
    kSession.fireAllRules();
}