Using the Embedded Enterprise Bean Container

This chapter demonstrates how to use the embedded enterprise bean container to run enterprise bean applications in the Java SE environment, outside of a Jakarta EE server.

Overview of the Embedded Enterprise Bean Container

The embedded enterprise bean container is used to access enterprise bean components from client code executed in a Java SE environment. The container and the client code are executed within the same virtual machine. The embedded enterprise bean container is typically used for testing enterprise beans without having to deploy them to a server.

Most of the services present in the enterprise bean container in a Jakarta EE server are available in the embedded enterprise bean container, including injection, container-managed transactions, and security. Enterprise bean components execute similarly in both embedded and Jakakarta EE environments, and therefore the same enterprise bean can be easily reused in both standalone and networked applications.

Developing Embeddable Enterprise Bean Applications

All embeddable enterprise bean containers support the features listed in Required Enterprise Bean Features in the Embeddable Container.

Required Enterprise Bean Features in the Embeddable Container
Enterprise Bean Feature	Description
Local session beans	Local and no-interface view stateless, stateful, and singleton session beans. All method access is synchronous. Session beans must not be web service endpoints.
Transactions	Container-managed and bean-managed transactions.
Security	Declarative and programmatic security.
Interceptors	Class-level and method-level interceptors for session beans.
Deployment descriptor	The optional `ejb-jar.xml` deployment descriptor, with the same overriding rules for the enterprise bean container in Jakarta EE servers.

Container providers are allowed to support the full set of features in enterprise beans, but applications that use the embedded container will not be portable if they use enterprise bean features not listed in Required Enterprise Bean Features in the Embeddable Container, such as the timer service, session beans as web service endpoints, or remote business interfaces.

Running Embedded Applications

The embedded container, the enterprise bean components, and the client all are executed in the same virtual machine using the same classpath. As a result, developers can run an application that uses the embedded container just like a typical Java SE application, as follows:

java -classpath mySessionBean.jar:containerProviderRuntime.jar:myClient.jar \
com.example.ejb.client.Main

In the above example, mySessionBean.jar is an enterprise bean JAR containing a local stateless session bean, containerProviderRuntime.jar is a JAR file supplied by the enterprise bean provider that contains the needed runtime classes for the embedded container, and myClient.jar is a JAR file containing a Java SE application that calls the business methods in the session bean through the embedded container.

In GlassFish Server, the runtime JAR that includes the classes for the embedded container is glassfish-embedded-all.jar.

Creating the Enterprise Bean Container

The jakarta.ejb.embedded.EJBContainer abstract class represents an instance of the enterprise bean container and includes factory methods for creating a container instance. The EJBContainer.createEJBContainer method is used to create and initialize an embedded container instance.

The following code snippet shows how to create an embedded container that is initialized with the container provider’s default settings:

EJBContainer ec = EJBContainer.createEJBContainer();

By default, the embedded container will search the virtual machine classpath for enterprise bean modules: directories containing a META-INF/ejb-jar.xml deployment descriptor, directories containing a class file with one of the enterprise bean component annotations (such as @Stateless), or JAR files containing an ejb-jar.xml deployment descriptor or class file with an enterprise bean annotation. Any matching entries are considered enterprise bean modules within the same application. Once all the valid enterprise bean modules have been found in the classpath, the container will begin initializing the modules. When the createEJBContainer method successfully returns, the client application can obtain references to the client view of any enterprise bean module found by the embedded container.

An alternate version of the EJBContainer.createEJBContainer method takes a Map of properties and settings for customizing the embeddable container instance:

Properties props = new Properties();
props.setProperty(...);
...
EJBContainer ec = EJBContainer.createEJBContainer(props);

Explicitly Specifying Enterprise Bean Modules to Be Initialized

Developers can specify exactly which enterprise bean modules the embedded container will initialize. To explicitly specify the enterprise bean modules initialized by the embedded container, set the EJBContainer.MODULES property.

The modules may be located either in the virtual machine classpath in which the embedded container and client code run, or alternately outside the virtual machine classpath.

To specify modules in the virtual machine classpath, set EJBContainer.MODULES to a String to specify a single module name, or a String array containing the module names. The embedded container searches the virtual machine classpath for enterprise bean modules matching the specified names:

Properties props = new Properties();
props.setProperty(EJBContainer.MODULES, "mySessionBean");
EJBContainer ec = EJBContainer.createEJBContainer(props);

To specify enterprise bean modules outside the virtual machine classpath, set EJBContainer.MODULES to a java.io.File object or an array of File objects. Each File object refers to an enterprise bean JAR file, or a directory containing an expanded enterprise bean JAR file:

Properties props = new Properties();
File ejbJarFile = new File(...);
props.setProperty(EJBContainer.MODULES, ejbJarFile);
EJBContainer ec = EJBContainer.createEJBContainer(props);

Looking Up Session Bean References

To look up session bean references in an application using the embedded container:

Use an instance of EJBContainer to retrieve a javax.naming.Context object.

Call the EJBContainer.getContext method to retrieve the Context object:
```
EJBContainer ec = EJBContainer.createEJBContainer();
Context ctx = ec.getContext();
```
References to session beans can then be obtained using the portable JNDI syntax detailed in Portable JNDI Syntax. For example, to obtain a reference to MySessionBean, a local session bean with a no-interface view, use the following code:
```
MySessionBean msb = (MySessionBean)
            ctx.lookup("java:global/mySessionBean/MySessionBean");
```

Shutting Down the Enterprise Bean Container

To shut down the embedded container:

From the client, call the close method of the instance of EJBContainer.
```
EJBContainer ec = EJBContainer.createEJBContainer();
...
ec.close();
```
While clients are not required to shut down EJBContainer instances, doing so frees resources consumed by the embedded container. This is particularly important when the virtual machine under which the client application is running has a longer lifetime than the client application.

The standalone Example Application

The standalone example application demonstrates how to create an instance of the embedded enterprise bean container in a JUnit test class and call a session bean business method.

Overview of the standalone Example Application

Testing the business methods of an enterprise bean in a unit test allows developers to exercise the business logic of an application separately from the other application layers, such as the presentation layer, and without having to deploy the application to a Jakarta EE server.

The standalone example has two main components: StandaloneBean, a stateless session bean, and StandaloneBeanTest, a JUnit test class that acts as a client to StandaloneBean using the embedded container.

StandaloneBean is a simple session bean exposing a local, no-interface view with a single business method, returnMessage, which returns "Greetings!" as a String:

@Stateless
public class StandaloneBean {

    private static final String message = "Greetings!";

    public String returnMessage() {
        return message;
    }

}

StandaloneBeanTest calls StandaloneBean.returnMessage and tests that the returned message is correct. First, an embedded container instance and initial context are created within the setUp method, which is annotated with org.junit.Before to indicate that the method should be executed before the test methods:

@Before
public void setUp() {
    ec = EJBContainer.createEJBContainer();
    ctx = ec.getContext();
}

The testReturnMessage method, annotated with org.junit.Test to indicate that the method includes a unit test, obtains a reference to StandaloneBean through the Context instance, and calls StandaloneBean.returnMessage. The result is compared with the expected result using a JUnit assertion, assertEquals. If the string returned from StandaloneBean.returnMessage is equal to "Greetings!" the test passes:

@Test
public void testReturnMessage() throws Exception {
    logger.info("Testing standalone.ejb.StandaloneBean.returnMessage()");
    StandaloneBean instance = (StandaloneBean)
            ctx.lookup("java:global/classes/StandaloneBean");
    String expResult = "Greetings!";
    String result = instance.returnMessage();
    assertEquals(expResult, result);
}

Finally, the tearDown method, annotated with org.junit.After to indicate that the method should be executed after all the unit tests have run, closes the embedded container instance:

@After
public void tearDown() {
    if (ec != null) {
        ec.close();
    }
}

To Run the standalone Example Application Using NetBeans IDE

From the File menu, choose Open Project.
In the Open Project dialog box, navigate to:
```
jakartaee-examples/tutorial/ejb
```
Select the standalone folder and click Open Project.
In the Projects tab, right-click standalone and select Test.

This will execute the JUnit test class StandaloneBeanTest. The Output tab shows the progress of the test and the output log.

To Run the standalone Example Application Using Maven

In a terminal window, go to:

jakartaee-examples/tutorial/ejb/standalone/

Enter the following command:
```
mvn install
```
This command compiles and packages the application into an JAR file, and executes the JUnit test class StandaloneBeanTest.