How to Troubleshoot Apps for the Modern Connected Worker
Ejb3online Final 060208v2
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tech facts at your fingertips
CONTENTS INCLUDE:
What is EJB3?
Dependency Injection in EJB 3
n
n
Resource Injection
n
Injection of EJB References
n
Injecting JPA Resources
n
Injecting Spring Beans in EJB 3
n
Hot Tips and more...
By Debu Panda
WHAT IS EJB 3? DEPENDENCY INJECTION IN EJB 3
Enterprise JavaBeans (EJB) is a platform for building portable, With EJB 3, dependency injection has greatly simplified accessing
reusable, and scalable business applications using the Java both EJB resources—such as JDBC DataSource, JMS Objects,
programming language. Since its initial incarnation, EJB has and JPA Entity Manager—and services—such as Timer, User
been touted as a component model or framework that lets you Transaction, and Web Services. You will find this Refcard useful
when building enterprise Java applications with EJB 3 and JPA.
build enterprise Java applications without having to reinvent
It lists all metadata annotations, describes them and provides
services such as transactions, security, and automated persistence
examples. It also provides descriptions for XML elements that
for building an application. you can use for injection.
EJB 3 greatly simplifies development by adopting a POJO Most enterprise Java applications use external resources
programming model. As shown in the following figure an and services such as Data Source, EJB, or web services. EJB 3
annotation transforms a simple POJO to an EJB. makes using resources and services simpler by implementing
dependency injection.
Dependency injection allows you to simply declare component
J + @ = dependencies and let the EJB container deal with the complexities
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of instantiating, initializing, and sequencing resources and
supplying service or resource references to clients as required.
POJO Annotation EJB Development frameworks like Spring framework originally
popularized dependency injection.
EJB 3 not only simplifies development of session and message In EJB 3, you may think of dependency injection as the inverse of
driven beans but it also radically simplifies the persistence JNDI. It is the responsibility of the container to inject an object
model by implementing a simplified Object-Relational Mapping based on the dependency declaration. The figure below com-
approach similar to Oracle TopLink and JBoss Hibernate as a pares dependency injection with JNDI.
part of the Java Persistence API. Note that JPA replaces EJB
2 CMP Entity beans in the EJB 3 spec, while being available
outside of the Java EE container. Resources
Lookup
Following is an example of a simple EJB 3 Stateless session bean. EJB JNDI lookup
import javax.ejb.Stateless; Beans
import ejb3inaction.example.persistence.Bid;
Dependency Injection in EJB 3
@Stateless
public class PlaceBidBean implements PlaceBid {
Resources Dependency
...
injection
Container Injection EJB
public PlaceBidBean() {}
Beans
public Bid addBid(Bid bid) {
System.out.println(“Adding bid, bidder ID=”
+ bid.getBidderID()
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+ “, item ID=” + bid.getItemID() (They’re free!)
+ “, bid amount=”
+ bid.getBidAmount() + “.”);
n Authoritative content
return save(bid);
n Designed for developers
} n Written by top experts
... n Latest tools & technologies
} n Hot tips & examples
import javax.ejb.Local;
n Bonus content online
import ejb3inaction.example.persistence.Bid;
n New issue every 1-2 weeks
@Local public interface PlaceBid { Subscribe Now for FREE!
Bid addBid(Bid bid);
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}
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2. 2
Dependency Injection in EJB 3
tech facts at your fingertips
The following annotations can be used in a field or a setter method
DEPENDENCY INJECTION IN EJB 3 continued for dependency injection. However, these annotations may also
be applied at the class level for defining dependencies and then
used with JNDI look up.
Note that annotations and descriptors are not
Hot mutually exclusive. In fact, you can use both
Annotations Usage Components that
Tip can use
together. Deployment descriptor entries override javax.annotation.Resource Dependency injection EJB, Web,
configuration values specified using metadata of resources such as Application Client
DataSource, and JMS
annotations. objects
javax.ejb.EJB Dependency injection EJB, Web,
of Session beans Application Client
You can use either metadata annotations or XML descriptors
javax.xml.ws.WebServiceRef Dependency injection EJB, Web,
to use dependency injection. of Web services Application Client
Refer to the following Java EE 5 specifications and XML schema javax.persistence. Dependency injection EJB, Web
PersistenceContext of container-managed
for more information on dependency injection.
EntityManager
JSR 220 javax.persistence. Dependency injection EJB, Web
Enterprise JavaBeans 3.0: PersistenceUnit of EntityManagerFactory
http://www.jcp.org/en/jsr/detail?id=220
JSR 224 RESOURCE INJECTION
Java API for XML-Based Web Services (JAX-WS) 2.0:
http://jcp.org/en/jsr/detail?id=224 javax.annotation.Resource
The @Resource annotation is used to inject any of the following:
JSR 250:
JDBC data sources, JMS connection factories, JMS destinations,
Common Annotations for the Java Platform:
mail resource, environment entries, timer service, UserTransaction,
http://www.jcp.org/en/jsr/detail?id=250
and EJBContext.
Schema for EJB 3 deployment descriptor:
The following table shows attributes for the @Resource annotation.
http://java.sun.com/xml/ns/javaee/ejb-jar_3_0.xsd
Schema that defines common schema components: Parameter Type Description Default
http://java.sun.com/xml/ns/javaee/javaee_5.xsd authentication enum The type of authentication CONTAINER
Type Authentication required for accessing the
Dependency injection is supported only on managed classes Type resource. The CONTAINER
{CONTAINER, value means that the
and not on regular POJO. APPLICATION} container’s security context
is used for the resource. The
APPLICATION value means
Dependency injection is supported only on that authentication for the
Hot managed classes such as Session Beans or In-
resource must be provided
Tip by the application.
terceptors and not on regular POJO. Hence you name String The referred resources is “”
bound under this name in
cannot use injection on helper classes. the enviornment-naming
context as java:comp/
env/<Name>
The following table depicts what type of managed classes can
type Object Type of the resource Object.class
inject what objects. being referenced. Example:
javax.sql.DataSource
Resources Stateless Stateful MDB Interceptors
shareable Boolean Specifies whether the True
JDBC DataSource Yes Yes Yes Yes resource can be shared.
JMS Destinations, Yes Yes Yes Yes description String The description of the “”
Connection Factories resource.
mappedName String A vendor-specific name “”
Mail Resources Yes Yes Yes Yes
that the resource may be
UserTransaction Yes Yes Yes Yes mapped to, as opposed to
the JNDI name.
Environment Entries Yes Yes Yes Yes
EJBContext Yes Yes Yes No You can inject a resource at the field or setter method level.
Timer Service Yes No Yes No The following example shows data source injection at the field level:
@Resource(name=”jdbc/ActionBazaarDS”)
Web Service reference Yes Yes Yes Yes
private DataSource dataSource;
EnityManager, Yes Yes Yes Yes
EntityManagerFactory The following code shows data source injection at the setter
method level:
Java EE 5 introduced several metadata annotations as part of private DataSource dataSource;
JSR 250. Although primarily geared toward EJB, these annota- @Resource(name=”jdbc/ActionBazaarDB”)
public void setDataSource(DataSource dataSource) {
tions also apply to Java EE components such as Servlets, JSF
this.dataSource = dataSource;
managed beans, and application clients. }
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3. 3
Dependency Injection in EJB 3
tech facts at your fingertips
resource-env-ref
RESOURCE INJECTION continued
The resource-env-ref is used to specify references to JMS
destination resources such as a Queue or Topic.
Element/Attribute Name Description
Although setter injection might seem like a
Hot resource-env-ref-name The name used to bind the referenced JMS
Tip little more work, it provides a couple of distinct destination to the ENC. Same as the name
element in the @Resource annotation.
advantages. First, it is easier to unit-test by
mapped-name A vendor-specific global JNDI name for the
invoking the public setter method from a testing referenced JMS destination.
framework like JUnit. Second, it is easier to put resource-env-type Type of JMS destination referenced, such as javax.
jms.Queue or javax.jms.Topic.
initialization code in the setter if you need it.
injection-target Target where the referenced destination is
injected when dependency injection is used.
EJB 3 allows you to explicitly specify a global JNDI name using
<resource-env-ref>
the mappedName parameter of the @Resource annotation. For <resource-env-ref-name>jms/OrderBillingQueue</resource-env-ref-name>
example, if you’re using the Oracle Application Server and you <resource-env-ref-type>
have a data source with a global JNDI name of jdbc/OracleDS, javax.jms.Destination
you can specify the resource mapping as follows: </resource-env-ref-type>
<injection-target>
@Resource(name=”jdbc/ActionBazaarDS”, mappedName=”jdbc/ <injection-target-class>
OracleDS”) ejb3inaction.example.buslogic.PlaceOrderBean
private javax.jdbc.DataSource myDB; </injection-target-class>
<injection-target-name>billingQueue</injection-target-name>
XML elements to define Resource Injection </injection-target>
</resource-env-ref>
If you are using deployment descriptor (ejb-jar.xml) instead of
annotations, then you must use resource-ref, resource-env-ref env-entry
or env-entry XML elements to define dependencies. The env-entry defines environment entries for an EJB.
resource-ref Element/Attribute Name Description
The resource-ref is used to specify resource references. env-entry-name The name used in the environment entry in
Example: data source and JMS connection factories. the ENC. Same as the name element in the
@Resource annotation.
Element/Attribute Name Description env-entry-type Type of the env entry used. Legal types are
java.lang.Boolean, java.lang.Byte, java.lang.
res-ref-name The name used to bind the referenced resource
Character, java.lang.String, java.lang.Short,
into the ENC. Same as the name element in the
java.lang.Integer, java.lang.Long, java.lang.Float,
@Resource annotation.
and java.lang.Double.
mapped-name A vendor-specific global JNDI name for the
env-entry-value Value specified for the environment entry.
referenced resource.
injection-target Target where the referenced destination is
res-type Fully qualified class of the type of resource
injected when dependency injection is used.
referenced. Example: javax.sql.DataSource.
res-auth Authentication type for the resource. Valid values The injection-target defines the name of a class and a name
are Container or Application. (field or property) within that class into which a resource,
res-sharing-scope Specifies whether multiple beans can share EJB, or entity manager should be injected as we saw in the
the resource. Valid values are Shareable and above examples.
Unshareable
injection-target Target where the referenced resource is injected Element/Attribute Name Description
when dependency injection is used.
injection-target-class The fully qualified name of the class into which a
resource, EJB, or entity manager should be injected.
<resource-ref>
injection-target-name Name of the injection target, i.e., the name of the
<res-ref-name>jdbc/ActionBazaarDS</res-ref-name> property or field in the injection target class.
<res-type>javax.sql.DataSource</res-type>
<res-auth>Container</res-auth>
<res-sharing-scope>Shareable</res-sharing-scope>
INJECTION OF SESSION EJB REFERENCES
<injection-target>
Like resource injection, you can inject Session bean references
<injection-target-class>
into another EJB or other managed class using annotations
actionbazaar.buslogic.BidManagerBean</injection-target-class>
or deployment XML. If you prefer annotations you can use
<injection-target-name>dataSource</injection-target-name>
@javax.ejb.EJB annotations to inject either remote or local
</injection-target>
EJB references. Using deployment XML, you can inject
</resource-ref> remote EJB references with ejb-ref and local EJB references
with ejb-local-ref.
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4. 4
Dependency Injection in EJB 3
tech facts at your fingertips
@javax.ejb.EJB
Injects a session bean reference into a field or method. EJB 3 specification does not require
Hot injecting references of remote EJB into a
Parameter Type Description Default Tip
different instance of container. For example
name String The name used to bind the “”
referenced EJB to the ENC.
if you have an EJB with a remote interface
deployed into an instance of a container,
beanInterface Class The bean interface used to access Object.
the EJB class EJB 3 specification does not require inject-
mappedName String Type of the resource being referenced. “”
ing instance of that EJB into another EJB
Example: javax.sql.DataSource deployed in another container.
beanName String Specifies whether the resource can “”
be shared.
description String INJECTINg JPA RESOURCES
@EJB(name=”BidManagerRemote”) The JPA EntityManager is the bridge between the OO and
private BidManager bidManager; relational worlds as depicted in the following figure.
You must not inject a Stateful session bean
Hot
Save SQL
into a stateless object, such as a stateless Object
EntityManager
Tip
Relational
Database
Retrieve Results
session bean or servlet that may be
shared by multiple concurrent clients (you
should use JNDI in such cases instead). JPA supports two types of EntityManager: container-managed
However, injecting an instance of a state- and application-managed. As the name suggests the lifecycle
less session bean into a stateful session of the container manages container-managed EntityManager
bean is perfectly legal. whereas the lifecycle (creation, destruction) is performed by
application. An application-managed EntityManager is created
from an EntityManagerFactory.
ejb-local-ref
Injecting container-managed EntityManager
Used to specify a dependency on the local interface of a
You can inject a container-managed EntityManager (either
session bean.
transaction scoped or extended) using @javax.persistence.
Element/Attribute Name Description PersistenceContext annotation.
ejb-ref-name The name used to bind the referenced EJB to @javax.persistence.PersistenceContext
the ENC. Same as the name element in the @EJB
annotation. ejb-ref-name must be specified. The following table defines the parameters/attributes of this
annotation.
ejb-link The name of the target enterprise bean. This
optional setting is used to link an EJB reference to Parameter Type Description Default
a target enterprise bean.
name String The name used to bind “”
local The EJB 3 local business interface. the referenced persistence
context to the ENC
ref-type The EJB reference type, i.e. “session”.
unitName String Name of the persistence unit “”
injection-target Target where the EJB reference is injected when referenced
dependency injection is used.
type Persistence Type of persistence context, TRANSACTION
ContextType i.e., Transaction or Extended.
ejb-ref Extended is supported only in
stateful session beans.
Used to specify a dependency on the remote interface of a
session bean. properties Persistence A name value-pair of vendor- {}
Property[] specific persistence properties
Element/Attribute Name Description
You can inject a transaction scoped EntityManager as follows:
ejb-ref-name The name used to bind the referenced EJB to
the ENC. Same as the name element in the @EJB @PersistenceContext(unitName=”actionBazaar”)
annotation. ejb-ref-name must be specified. private EntityManager entityManager;
ejb-link The name of the target enterprise bean. This An extended scoped EntityManager can only used in a stateful
optional setting is used to link an EJB reference session bean as in the following example:
to a target enterprise bean.
@Stateful
remote The EJB 3 remote business interface type. @TransactionAttribute(TransactionAttributeType.NOT_SUPPORTED)
ref-type The EJB reference type, i.e. “session”. public class PlaceOrderBean implements PlaceOrder {
@PersistenceContext(unitName = “actionBazaar”, type =
injection-target Target where the EJB reference is injected when
PersistenceContextType.EXTENDED)
dependency injection is used.
EntityManager em;
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5. 5
Dependency Injection in EJB 3
tech facts at your fingertips
Injecting JPA Resources, continued
INJECTINg WEB SERvICE REFERENCES
The persistence-context-ref is similar to @PersistenceContext;
it defines references to a container-managed entity manager. @javax.xml.ws.WebServiceRef
Element Description
Element/Attribute Name Description
name The JNDI name for the web service.
persistence-context-ref- The name used to bind the referenced persistence
name context to the ENC. Same as the name element in wsdlLocation The WSDL location for the service. If not specified,
then it is derived from the referenced service class.
the @PersistenceContext annotation.
type The Java type of the resource.
persistence-unit-name Name of the persistence unit referenced.
value The service class, always a type extending javax.xml.
persistence-context-type Type of persistence context, i.e., Transaction or ws.Service.
Extended. Extended is supported only in stateful
mappedName Vendor-specific global JNDI name for the service.
session beans.
persistence-property A name value-pair of vendor-specific persistence You can inject an endpoint interface as follows:
properties. @WebServiceRef(TrackDeliveryService.class)
injection-target Target where the EntityManager is injected when private TrackDeliverySEI deliveryService;
dependency injection is used.
You can inject a service interface as follows:
<persistence-context-ref> @WebServiceRef
private TrackingService service;
<persistence-context-ref-name>
ActionBazaar service-ref
</persistence-context-ref-name> The service-ref XML element is used to specify dependency on a
<persistence-unit-name>actionBazaar</persistence-unit-name> web service if you are using deployment descriptor. The following
<persistence-context-type>Transaction</persistence-context-type> table contains only the elements that are used from EJB clients.
<injection-target>
<injection-target-class> Element/Attribute Name Description
ejb3inaction.example.buslogic.PlaceBidBean service-ref-name The name used to bind the referenced web service
</injection-target-class> into the ENC. Same as the name element in the @
WebServiceRef annotation.
<injection-target-name>em</injection-target-name>
</injection-target> service-interface Fully qualified class for the JAX-WS service interface
the client depends on., i.e. javax.xml.rpc.Service.
</persistence-context-ref>
service-ref-type Type of service that will be returned.
Injecting EntityManagerFactory wsdl-file The URL location of the WSDL.
@javax.persistence.PersistenceUnit handler-chains Defines handler chain.
@Stateless injection-target Target where the web service reference is injected
when dependency injection is used.
public class ItemManagerBean implements ItemManager {
@PersistenceUnit The detailed schema for the service-ref can be found online at
private EntityManagerFactory entityManagerFactory; java.sun.com/xml/ns/javaee/javaee_web_services_client_1_2.xsd.
private EntityManager entityManager;
@PostConstruct
public void initialize() { INJECTINg SPRINg BEANS IN EJB 3
entityManager = entityManagerFactory.createEntityManager();
} The Spring Framework is one of the driving forces behind popular-
} izing the POJO programming model and dependency injection.
In this section we will examine how you can inject and use Spring
Parameter Type Description Default
POJOs into EJB 3 Session beans or Message Driven Beans.
name String The name used to bind “”
the referenced persistence
The Spring framework provides factory classes based on the follow-
context to the ENC ing abstract classes that you use to develop Spring-enabled EJBs.
unitName String Name of the persistence unit “”
Support Class Purpose
The persistence-unit-ref is similar to @PersistenceUnit that is AbstractStatelessSessionBean Used for Spring-enabled stateless session
beans.
used to define references to a persistence unit (i.e., entity
AbstractStatefulSessionBean Used for Spring-enabled stateful session
manager factory). beans.
AbstractJMSMessageDrivenBean Used for Spring-enabled JMS message-
Element/Attribute Name Description driven beans.
persistence-unit-ref-name The name used to bind the referenced persistence AbstractMessageDrivenBean Used for Spring-enabled connector-based
unit (EntityManagerFactory) to the ENC. Same MDBs.
as the name element in the @PersistenceUnit
annotation.
To use a Spring factory class to access a Spring bean, your EJB 3
persistence-unit-name Name of the persistence unit referenced. bean class must implement the onEjbCreate() method.
injection-target Target where the EntityManagerFactory is injected Below is the PlaceBidBean EJB 3 example transformed into a
when dependency injection is used.
Spring-enabled stateless session bean. Here the PlaceBidBean
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