Chapter 87. Basic Session EJB Component

Add essential EJB aspects to POJO classes
Deploy to server and test

87.1. Making POJO an EJB

87.1.1. Annotate Bean class with @javax.ejb.Stateless

import javax.ejb.Stateless;

...

@Stateless

public class GreeterEJB implements Greeter {

Other types include @Stateful, @Singleton, and @MessageDriven

87.1.2. Annotate Interface with @javax.ejb.Remote

import javax.ejb.Remote;

...

@Remote

public interface Greeter {

Defines business remote interface for EJB

Alternately can define @Remote(Interface.class) within EJB bean class

@Stateless

@Remote(Greeter.class)

public class GreeterEJB implements Greeter {

87.1.3. Optionally Annotate Empty Interface Extending POJO Business Interface

public interface Greeter {

    String sayHello(String name) throws BadRequestException;


    Greeting sayHello(Name name) throws BadRequestException;

}

import javax.ejb.Remote;


@Remote

public interface GreeterRemote extends Greeter {

}

Useful when EJB implements legacy interface

EJB must then implement Remote or declare @Remote

@Stateless

public class GreeterEJB implements GreeterRemote {

@Stateless

@Remote(GreeterRemote.class)

public class GreeterEJB implements Greeter {

87.1.4. @PostConstruct/@PreDestory

Optional callbacks to initialize and destroy resources

    @PostConstruct

    public void init() {

        logger.info("*** GreeterEJB:init({}) ***", super.hashCode());

    }

Called after all resources have been injected and before first business method called
No args, void return, no declared checked exceptions
Used to ready bean to satisfy business methods



    @PreDestroy

    public void destroy() {

        logger.info("*** GreeterEJB:destroy({}) ***", super.hashCode());

    }

If called, will be after last business method

87.2. EJB Module

EJB artifact looks very much like a normal POJO archive
Since our EJB is 100% annotation-based, we have no need for META-INF/ejb-jar.xml descriptor

$ jar tf target/ejb-basic-ejb-4.0.0-SNAPSHOT.jar 
...
info/ejava/examples/ejb/basic/ejb/BadRequestException.class
info/ejava/examples/ejb/basic/ejb/Greeter.class
info/ejava/examples/ejb/basic/ejb/GreeterEJB.class
info/ejava/examples/ejb/basic/ejb/GreeterRemote.class
info/ejava/examples/ejb/basic/dto/Name.class
info/ejava/examples/ejb/basic/dto/Greeting.class
...

87.2.1. Source EJB Module

|-- pom.xml
`-- src                                                                                                                                                                                       
    |-- main                                                                                                                                                                                  
    |   `-- java                                                                                                                                                                              
    |       `-- info                                                                                                                                                                          
    |           `-- ejava                                                                                                                                                                     
    |               `-- examples
    |                   `-- ejb
    |                       `-- basic
    |                           |-- dto
    |                           |   |-- Greeting.java
    |                           |   `-- Name.java
    |                           `-- ejb
    |                               |-- BadRequestException.java
    |                               |-- GreeterEJB.java
    |                               |-- Greeter.java
    |                               `-- GreeterRemote.java
    `-- test
        |-- java
        |   `-- info
        |       `-- ejava
        |           `-- examples
        |               `-- ejb
        |                   `-- basic
        |                       `-- pojo
        |                           `-- GreeterTest.java
        `-- resources
            `-- log4j.xml

Module contains separate source trees for production and unit test code

87.3. Naked EJB-based Deployment

EJB module deployed either as naked EJB

17:19:52,979 INFO  [org.jboss.as.ejb3.deployment.processors.EjbJndiBindingsDeploymentUnitProcessor] (MSC service thread 1-1) 
JNDI bindings for session bean named GreeterEJB in deployment unit deployment "ejb-basic-ejb.jar" are as follows:

        java:global/ejb-basic-ejb/GreeterEJB!info.ejava.examples.ejb.basic.ejb.GreeterRemote
        java:app/ejb-basic-ejb/GreeterEJB!info.ejava.examples.ejb.basic.ejb.GreeterRemote
        java:module/GreeterEJB!info.ejava.examples.ejb.basic.ejb.GreeterRemote
        java:jboss/exported/ejb-basic-ejb/GreeterEJB!info.ejava.examples.ejb.basic.ejb.GreeterRemote
        java:global/ejb-basic-ejb/GreeterEJB
        java:app/ejb-basic-ejb/GreeterEJB
        java:module/GreeterEJB

17:19:53,012 INFO  [org.jboss.weld.deployer] (MSC service thread 1-1) JBAS016005: Starting Services for CDI deployment: ejb-basic-ejb.jar
17:19:53,029 INFO  [org.jboss.weld.deployer] (MSC service thread 1-2) JBAS016008: Starting weld service for deployment ejb-basic-ejb.jar
17:19:53,485 INFO  [org.jboss.as.server] (DeploymentScanner-threads - 1) JBAS018559: Deployed "ejb-basic-ejb.jar" (runtime-name : "ejb-basic-ejb.jar")

JBoss server prints out JNDI names to access EJB through...
Derive remote client JNDI name from "exported" name
- ejb-basic-ejb/GreeterEJB!info.ejava.examples.ejb.basic.ejb.GreeterRemote
Local and No-interface interfaces are not exposed to remote clients

87.4. Maven Aspects: EJB

packaging=ejb: Required in order for downstream containers to recognize as EJB component
javax.ejb:javax.ejb-api: Supplies EJB API definitions
maven-ejb-plugin: Builds EJB and optional ejbclient artifact




<project>

...

    <packaging>ejb</packaging>



    <dependencies>

...

        <dependency>

            <groupId>javax.ejb</groupId>

            <artifactId>javax.ejb-api</artifactId>

            <scope>provided</scope>

        </dependency>

...        

    </dependencies>

    

    <build>

        <plugins>

              <!-- tell EJB plugin to create a client-jar -->

            <plugin>

                <groupId>org.apache.maven.plugins</groupId>

                <artifactId>maven-ejb-plugin</artifactId>

                <configuration>

                    <generateClient>true</generateClient>

                    <clientExcludes>

                        <clientExclude>**/ejb/*Local.class</clientExclude>

                        <clientExclude>**/ejb/*EJB.class</clientExclude>

                    </clientExcludes>

                </configuration>

            </plugin>

        </plugins>

    </build>    

</project>

87.5. JBoss Session EJB Pooling

Initialized EJB bean instances can be cached in a pool
Instances from the pool can be re-used rather than destroy and re-intialize a new instance

JBoss pools singleton and stateful session beans by default


# standalone/configuration/standalone.xml

<session-bean>

    <stateful default-access-timeout="5000" cache-ref="simple" passivation-disabled-cache-ref="simple"/>

    <singleton default-access-timeout="5000"/>

</session-bean>

JBoss defines a stateless session bean pool for use but left unassigned


# standalone/configuration/standalone.xml

<pools>

    <bean-instance-pools>

        <strict-max-pool name="slsb-strict-max-pool" max-pool-size="20" instance-acquisition-timeout="5" instance-acquisition-timeout-unit="MINUTES"/>

        <strict-max-pool name="mdb-strict-max-pool" max-pool-size="20" instance-acquisition-timeout="5" instance-acquisition-timeout-unit="MINUTES"/>

    </bean-instance-pools>

</pools>

No pooling can be costly when initialization costs are high

Stateless and MDB EJB pooling can be enabled globally


# standalone/configuration/standalone.xml

<session-bean>

    <stateless>

        <bean-instance-pool-ref pool-name="slsb-strict-max-pool"/>

    </stateless>

    <stateful default-access-timeout="5000" cache-ref="simple" passivation-disabled-cache-ref="simple"/>

    <singleton default-access-timeout="5000"/>

</session-bean>

Pooling can be costly when initialization costs are low

Stateless and MDB EJB pooling can be enabled on a per-application(*)/per-EJB(GreeterEJB) basis


# META-INF/jboss-ejb3.xml

<jboss:ejb-jar xmlns:jboss="http://www.jboss.com/xml/ns/javaee" 

    xmlns="http://java.sun.com/xml/ns/javaee"

    xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" 

    xmlns:s="urn:security" 

    xmlns:c="urn:clustering:1.0"

    xmlns:p="urn:ejb-pool:1.0"

    xsi:schemaLocation="http://www.jboss.com/xml/ns/javaee http://www.jboss.org/j2ee/schema/jboss-ejb3-2_0.xsd

                     http://java.sun.com/xml/ns/javaee http://java.sun.com/xml/ns/javaee/ejb-jar_3_1.xsd"

    version="3.1" 

    impl-version="2.0">



    <assembly-descriptor>

        <!-- defines EJB pool else not pooled -->

        <p:pool>

          <ejb-name>*</ejb-name>

          <p:bean-instance-pool-ref>slsb-strict-max-pool</p:bean-instance-pool-ref>

        </p:pool>    

    </assembly-descriptor>

</jboss:ejb-jar>

87.6. Summary

Added necessary aspects to POJO to make it an EJB
- Annotated class as @Stateless
- Annotated remote interface as @Remote
Deployed to server
Obtained JNDI name of naked EJB-based @Remote
- (component-name)/(ejb-name)!(remote-interface-name)
- ejb-basic-ejb/GreeterEJB!info.ejava.examples.ejb.basic.ejb.GreeterRemote