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Singleton Startup Ordering

This examples shows in practice the @Startup and @DependsOn annotations on singleton EJB’s.

Run the tests

mvn clean test

The scenario

  • The example is composed by three singleton beans: SingletonA, SingletonB, SingletonC.

  • The three EJB’s contains a @PostConstruct annotation for the init method that is executed after dependency injection is done to perform any initialization. This method is invoked before the class is put into service.

  • The init method store the name of the bean class that is been initialized in the Supervisor bean.

  • The Supervisor bean is annotated with @ApplicationScoped to be able to share the list of bean names stored in the records attribute.

  • SingletonA and SingletonB are annotated with @Startup which means they are going to initialized upon application startup. SingletonC will be initialized until the bean is going to be used in later injection point.

  • SingletonB is annotated with @DependsOn("SingletonA") to enforce a initialization order with respect to SingletonA.

SingletonA.java: Singleton EJB annotated with @Startup. It depends on the EJB Supervisor.

package org.foo;

import jakarta.annotation.PostConstruct;
import jakarta.ejb.Singleton;
import jakarta.ejb.Startup;
import jakarta.inject.Inject;
import java.util.logging.Logger;

@Singleton
@Startup
public class SingletonA {

    @Inject
    Supervisor supervisor;

    private final static Logger LOGGER = Logger.getLogger(SingletonA.class.getName());


    @PostConstruct
    public void init() {
        LOGGER.info("Hi from init in class: " + this.getClass().getName());
        supervisor.addRecord(this.getClass().getSimpleName());
    }
}

SingletonB.java: Singleton EJB annotated with @Startup and DependsOn. It depends on the EJB Supervisor.

package org.foo;

import jakarta.annotation.PostConstruct;
import jakarta.ejb.DependsOn;
import jakarta.ejb.Singleton;
import jakarta.ejb.Startup;
import jakarta.inject.Inject;
import java.util.logging.Logger;

@Singleton
@Startup
@DependsOn("SingletonA")
public class SingletonB {

    @Inject
    Supervisor supervisor;

    private final static Logger LOGGER = Logger.getLogger(SingletonB.class.getName());

    @PostConstruct
    public void init() {
        LOGGER.info("Hi from init in class: " + this.getClass().getName());
        supervisor.addRecord(this.getClass().getSimpleName());
    }
}

SingletonC.java: Singleton EJB. It depends on the EJB Supervisor.

import jakarta.annotation.PostConstruct;
import jakarta.ejb.Singleton;
import jakarta.inject.Inject;
import java.util.logging.Logger;

@Singleton
public class SingletonC {
    @Inject
    Supervisor supervisor;

    private final static Logger LOGGER = Logger.getLogger(SingletonC.class.getName());

    @PostConstruct
    public void init() {
        LOGGER.info("Hi from init in class: " + this.getClass().getName());
        supervisor.addRecord(this.getClass().getSimpleName());

    }

    public String hello() {
        return "Hello from SingletonC.class";
    }
}

Supervisor.java: Applicaiton scoped Bean that keep track of a list of Bean Names.

import jakarta.enterprise.context.ApplicationScoped;
import java.util.ArrayList;
import java.util.List;

@ApplicationScoped
public class Supervisor {
    private final List<String> records = new ArrayList<>();

    public void addRecord(String beanClass){
        records.add(beanClass);
    }

    public String getRecord(){
        return records.toString();
    }
}

The tests

  • The class TestSingletonStartupOrder.java contains two test that are executed in order via the annotation @FixMethodOrder(MethodSorters.NAME_ASCENDING)

  • firstTest: assert true if and only if the records stored in the Supervisor.record are equals to [SingletonA, SingletonB]. Notice that the order is validated too. In this test we don’t expect to see SingletonC initialized since it’s not annotated with @Startup.

  • secondTest: This test inject SingletonC as a parameter in the tests, therefore it asserts to true if and only if the records stored in the Supervisor.record are equals to [SingletonA, SingletonB, SingletonC]

TestSingletonStartupOrder.java

import org.jboss.arquillian.container.test.api.Deployment;
import org.jboss.arquillian.junit.Arquillian;
import org.jboss.shrinkwrap.api.ShrinkWrap;
import org.jboss.shrinkwrap.api.asset.StringAsset;
import org.jboss.shrinkwrap.api.spec.WebArchive;
import org.junit.FixMethodOrder;
import org.junit.Test;
import org.junit.runner.RunWith;
import org.junit.runners.MethodSorters;
import org.foo.SingletonA;
import org.foo.SingletonB;
import org.foo.SingletonC;
import org.foo.Supervisor;

import java.util.logging.Logger;

import static junit.framework.TestCase.assertTrue;


@RunWith(Arquillian.class)
@FixMethodOrder(MethodSorters.NAME_ASCENDING)
public class TestSingletonStartupOrder {
    private final static Logger LOGGER = Logger.getLogger(TestSingletonStartupOrder.class.getName());

    @Deployment()
    public static WebArchive createDeployment() {
        final WebArchive webArchive = ShrinkWrap.create(WebArchive.class, "test.war")
                                                .addClass(SingletonA.class)
                                                .addClass(SingletonB.class)
                                                .addClass(SingletonC.class)
                                                .addClass(Supervisor.class)
                                                .addAsWebInfResource(new StringAsset("<beans/>"), "beans.xml");
        return webArchive;
    }


    @Test
    public void firstTest(Supervisor supervisor) {
        LOGGER.info("SUPERVISOR: [" + supervisor.getRecord() + "]");
        assertTrue(supervisor.getRecord().equals("[SingletonA, SingletonB]"));
    }

    @Test
    public void secondTest(Supervisor supervisor, SingletonC singletonC) {
        LOGGER.info(singletonC.hello());
        LOGGER.info("SUPERVISOR: [" + supervisor.getRecord() + "]");
        assertTrue(supervisor.getRecord().equals("[SingletonA, SingletonB, SingletonC]"));
    }
}

About the Test architecture

The test cases from this project are built using Arquillian and TomEE Remote. The arquillian configuration can be found in src/test/resources/arquillian.xml

APIs Used