= Singleton Startup Ordering
:index-group: Session Beans
:jbake-type: page
:jbake-status: status=published

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


=== Run the tests
[source,java]
----
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`.

[source,java]
----
package org.foo;

import javax.annotation.PostConstruct;
import javax.ejb.Singleton;
import javax.ejb.Startup;
import javax.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`.

[source,java]
----
package org.foo;

import javax.annotation.PostConstruct;
import javax.ejb.DependsOn;
import javax.ejb.Singleton;
import javax.ejb.Startup;
import javax.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`.

[source,java]
----
import javax.annotation.PostConstruct;
import javax.ejb.Singleton;
import javax.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.

[source,java]
----
import javax.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`
[source,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`