Home > Articles > Programming > Java

  • Print
  • + Share This
This chapter is from the book

5.5 Local Interfaces

One of the new features added in the EJB 2.0 specification is local interfaces for session and entity beans. What are local interfaces and when do you use them?

The EJB examples we've presented so far have all had a home interface, remote interface, and bean implementation class. A client accesses an EJB through either its home interface with create()or through its remote interface using a business method. The EJB container intercepts method invocations and, in turn, calls the respective bean implementation method, or, in the case of create()with a stateless session bean, simply grabs a bean instance from the pool (if possible). Each call from the client to the bean is a remote invocation using the Java Remote Method Invocation (RMI) API. This means argument parameters and return values are copied, serialized, and transmitted remotely. While remote calls give an enterprise application its scalability and accessibility, RMI adds overhead to the network. Furthermore, while we do want certain EJBs to have remote clients (such as our MusicIterator EJB, MusicCart EJB, and Loan EJB presented earlier) some EJBs do not need remote clients.

To implement the Value List Iterator Pattern, we created a stateful MusicIter-ator EJB to interface with a stateless MusicPage EJB. Although a remote client could certainly bypass the front-end MusicIterator EJB and invoke methods on the MusicPage EJB directly, we anticipate that clients would rather use the convenient interface provided by the MusicIterator EJB. Thus, we presume that the only clients of MusicPage EJB will be instances of MusicIterator EJB. If we're willing to limit our deployment so that all instances of MusicIterator EJB and MusicPage EJB share the same Java Virtual Machine (JVM), then we can say that all clients of MusicPage EJB will be local.

What does it mean to be a local client? A local client runs in the same JVM as the bean it accesses. A local client may be a web component or another EJB, but not an application client. With remote access, the location of the EJB is transparent to the remote client (the remote EJB may execute in the same JVM, or it may be on a machine halfway around the world). Furthermore, argument parameters and return values are passed by reference with local calls. This increases performance, since no copies are made. Passing arguments by reference can be risky, however. Methods could use a reference to inadvertently modify an argument passed to it (this is called a side effect). Then, changes to the client's view of an object change the EJB's view as well.

The MusicPage EJB is a good candidate for local access because it is tightly coupled with the MusicIterator EJB. These two enterprise beans were designed to work in tandem, and limiting their execution to the same JVM makes sense in this case. Furthermore, argument passing involves read-only operations, so we don't need to worry about side effects to parameter objects.

Other common uses of local interfaces are with the Session Facade Pattern (see "Session Facade Pattern" on page 250) and entity bean container-managed persistence (see "Introducing Container-Managed Persistence" on page 278).

Implementation Guideline

It's also possible to implement an enterprise bean with both local and remote access, although this is not common in production environments. Since you cannot access an enterprise bean from an application client through its local interface (which is typically how you would test your EJB code), you should consider implementing remote access for testing and debugging.

Local Interface Implementation

How do you implement an EJB with local access? As you might guess, it's all a matter of the interfaces. Access to the create() methods is through the local home interface. Access to the bean's business methods is through the local interface. These interfaces are distinct from their "remote cousins" and extend different interfaces. Thus, the local home interface extends EJBLocalHome(instead of EJBHome) and the local interface extends EJBLocalObject (instead of EJBOb-ject). Since access is specifically not remote, do not specify RemoteException in the throws clause for any method in a local interface.

Let's update our filename conventions in Table 5.1 to include local and local home interfaces.

Figure 5-11 shows a class diagram of the classes and interfaces that we write for MusicPage EJB with local interfaces. Interface MusicPageLocalHome is the local home interface extending interface EJBLocalHome. Interface MusicPage-Local is the local interface extending interface EJBLocalObject. And finally, class MusicPageBean is the bean implementation class that implements class SessionBean(unchanged from the previous implementation). Class Contain-erProxyintercepts calls made through the local home and local interfaces and forwards them to the appropriate method in class MusicPageBean.

Figure 5-11 Class Diagram Showing the EJB Classes for a Session Bean with Local Interfaces

Table 5.1 Naming Conventions for EJB Class and Interface Names

EJB Class/Interface

Name

Example

Remote Interface

Bean Name

MusicPage

Home Interface

Bean Name + Home

MusicPageHome

Local Interface

Bean Name + Local

MusicPageLocal

Local Home Interface

Bean Name + LocalHome

MusicPageLocalHome

Bean Implementation Class

Bean Name + Bean

MusicPageBean


Before we show you the MusicPage EJB with local interfaces, let's review the component architecture of our MusicCart web application and add in characteristics of the EJBs. In Figure 5-12 we've noted EJB access (remote or local), as well as which EJBs are stateful session beans (SFSB) and which are stateless session beans (SLSB). Note that anytime access is remote, the client and server components may execute in different JVMs (and thus on different machines). For local access, the client and server components must run in the same JVM.

Figure 5-12 Architectural Overview of the Music Shopping Cart Enterprise Application

Local Home Interface

We define the local home interface in MusicPageLocalHome, shown in Listing 5.20. Note that this interface extends the EJBLocalHome interface. Method create()does not need a RemoteExceptionin its throwsclause and it returns a local interface object (MusicPageLocal) instead of a remote interface object.

Listing 5.20 MusicPageLocalHome.java

// MusicPageLocalHome.java
import javax.ejb.CreateException;
import javax.ejb.EJBLocalHome;

public interface MusicPageLocalHome extends EJBLocalHome {

  MusicPageLocal create() throws CreateException;
}

Local Interface

We define local interface MusicPageLocal in Listing 5.21 and extend it from interface EJBLocalObject. Note that none of the methods should have RemoteException in their throws clauses. Although the method names and signatures are all identical to their remote versions, we now pass parameters and return values by reference rather than by value.

Listing 5.21 MusicPageLocal.java

// MusicPageLocal.java
import javax.ejb.EJBLocalObject;
import java.util.*;

public interface MusicPageLocal extends EJBLocalObject {

  public ArrayList getTrackList(RecordingVO rec)
     throws NoTrackListException;

  public int getSize();
  public ArrayList getPage(int currentIndex,
     int pageSize);
}public interface MusicPageLocal extends EJBLocalObject { 

Bean Implementation Class

For local interfaces, what changes must be made to our MusicPageBeanimple-mentation class? The answer is none. Thus, unless the bean implementation code needs to make some changes because of the way method parameters and return objects are treated, no changes are required.

MusicIterator Client

We must also update the code in MusicIteratorBean.java (Listing 5.13 on page 160) to access client MusicPage EJB through the local interfaces. Here are the changes:

  • We no longer have to import class javax.rmi.PortableRemoteObject.

  • We change the declaration of state variable pageBeanfrom MusicPageto MusicPageLocal:

private MusicPageLocal pageBean = null;

  • Inside method ejbCreate(), we change the declaration of variable pageHomefrom MusicPageHometo MusicPageLocalHome.

  • Furthermore, we no longer need PortableRemoteObject.narrowto create a home object:

MusicPageLocalHome pageHome = (MusicPageLocalHome)objref;

Deployment Descriptor

The deployment descriptor must reflect changes to both the description of MusicPage EJB (we have local and local home interfaces) and to its client, MusicIterator EJB. The client now specifies the local and local home interfaces for accessing the MusicPage EJB. In assembling our components, we've placed both the MusicPage EJB and the MusicIterator EJB in the same JAR file. Listing 5.22 shows the new deployment descriptor for <ejb-jar>(the EJB JAR file). You might want to compare this deployment descriptor to Listing 5.9 on page 156 and Listing 5.14 on page 163.

Listing 5.22 Deployment Descriptor for MusicJAR

<ejb-jar>
  <display-name>MusicPageJAR</display-name>
  <enterprise-beans>
   <session>
     <display-name>MusicPageBean</display-name>
     <ejb-name>MusicPageBean</ejb-name>
     <local-home>MusicPageLocalHome</local-home>
     <local>MusicPageLocal</local>
     <ejb-class>MusicPageBean</ejb-class>
     <session-type>Stateless</session-type>
     <transaction-type>Bean</transaction-type>

   <env-entry>
   <env-entry-name>MusicDAOClass</env-entry-name>
   <env-entry-type>java.lang.String</env-entry-type>
   <env-entry-value>MusicDAOCloudscape</env-entry-value>
   </env-entry>

     <security-identity>
      <description></description>
      <use-caller-identity></use-caller-identity>
     </security-identity>

     <resource-ref>
      <res-ref-name>jdbc/MusicDB</res-ref-name>
      <res-type>javax.sql.DataSource</res-type>
      <res-auth>Container</res-auth>
      <res-sharing-scope>Shareable</res-sharing-scope>
     </resource-ref>
   </session>
   <session>
     <display-name>MusicIteratorBean</display-name>
     <ejb-name>MusicIteratorBean</ejb-name>
     <home>MusicIteratorHome</home>
     <remote>MusicIterator</remote>
     <ejb-class>MusicIteratorBean</ejb-class>
     <session-type>Stateful</session-type>
     <transaction-type>Bean</transaction-type>

     <ejb-local-ref>
      <ejb-ref-name>ejb/MusicPage</ejb-ref-name>
      <ejb-ref-type>Session</ejb-ref-type>
      <local-home>MusicPageLocalHome</local-home>
      <local>MusicPageLocal</local>
      <ejb-link>MusicPageBean</ejb-link>
     </ejb-local-ref>
     <security-identity>
      <description></description>
      <use-caller-identity></use-caller-identity>
     </security-identity>
   </session>
  </enterprise-beans>
</ejb-jar>

You'll note that descriptor tags for MusicPage EJB now include <local-home> and <local>. Also, the descriptor tags for MusicIterator EJB include <ejb-local-ref> (a local EJB reference to MusicPage EJB). As before, MusicPage EJB is a stateless session bean; MusicIterator EJB is a stateful session bean.

  • + Share This
  • 🔖 Save To Your Account

InformIT Promotional Mailings & Special Offers

I would like to receive exclusive offers and hear about products from InformIT and its family of brands. I can unsubscribe at any time.

Overview


Pearson Education, Inc., 221 River Street, Hoboken, New Jersey 07030, (Pearson) presents this site to provide information about products and services that can be purchased through this site.

This privacy notice provides an overview of our commitment to privacy and describes how we collect, protect, use and share personal information collected through this site. Please note that other Pearson websites and online products and services have their own separate privacy policies.

Collection and Use of Information


To conduct business and deliver products and services, Pearson collects and uses personal information in several ways in connection with this site, including:

Questions and Inquiries

For inquiries and questions, we collect the inquiry or question, together with name, contact details (email address, phone number and mailing address) and any other additional information voluntarily submitted to us through a Contact Us form or an email. We use this information to address the inquiry and respond to the question.

Online Store

For orders and purchases placed through our online store on this site, we collect order details, name, institution name and address (if applicable), email address, phone number, shipping and billing addresses, credit/debit card information, shipping options and any instructions. We use this information to complete transactions, fulfill orders, communicate with individuals placing orders or visiting the online store, and for related purposes.

Surveys

Pearson may offer opportunities to provide feedback or participate in surveys, including surveys evaluating Pearson products, services or sites. Participation is voluntary. Pearson collects information requested in the survey questions and uses the information to evaluate, support, maintain and improve products, services or sites, develop new products and services, conduct educational research and for other purposes specified in the survey.

Contests and Drawings

Occasionally, we may sponsor a contest or drawing. Participation is optional. Pearson collects name, contact information and other information specified on the entry form for the contest or drawing to conduct the contest or drawing. Pearson may collect additional personal information from the winners of a contest or drawing in order to award the prize and for tax reporting purposes, as required by law.

Newsletters

If you have elected to receive email newsletters or promotional mailings and special offers but want to unsubscribe, simply email information@informit.com.

Service Announcements

On rare occasions it is necessary to send out a strictly service related announcement. For instance, if our service is temporarily suspended for maintenance we might send users an email. Generally, users may not opt-out of these communications, though they can deactivate their account information. However, these communications are not promotional in nature.

Customer Service

We communicate with users on a regular basis to provide requested services and in regard to issues relating to their account we reply via email or phone in accordance with the users' wishes when a user submits their information through our Contact Us form.

Other Collection and Use of Information


Application and System Logs

Pearson automatically collects log data to help ensure the delivery, availability and security of this site. Log data may include technical information about how a user or visitor connected to this site, such as browser type, type of computer/device, operating system, internet service provider and IP address. We use this information for support purposes and to monitor the health of the site, identify problems, improve service, detect unauthorized access and fraudulent activity, prevent and respond to security incidents and appropriately scale computing resources.

Web Analytics

Pearson may use third party web trend analytical services, including Google Analytics, to collect visitor information, such as IP addresses, browser types, referring pages, pages visited and time spent on a particular site. While these analytical services collect and report information on an anonymous basis, they may use cookies to gather web trend information. The information gathered may enable Pearson (but not the third party web trend services) to link information with application and system log data. Pearson uses this information for system administration and to identify problems, improve service, detect unauthorized access and fraudulent activity, prevent and respond to security incidents, appropriately scale computing resources and otherwise support and deliver this site and its services.

Cookies and Related Technologies

This site uses cookies and similar technologies to personalize content, measure traffic patterns, control security, track use and access of information on this site, and provide interest-based messages and advertising. Users can manage and block the use of cookies through their browser. Disabling or blocking certain cookies may limit the functionality of this site.

Do Not Track

This site currently does not respond to Do Not Track signals.

Security


Pearson uses appropriate physical, administrative and technical security measures to protect personal information from unauthorized access, use and disclosure.

Children


This site is not directed to children under the age of 13.

Marketing


Pearson may send or direct marketing communications to users, provided that

  • Pearson will not use personal information collected or processed as a K-12 school service provider for the purpose of directed or targeted advertising.
  • Such marketing is consistent with applicable law and Pearson's legal obligations.
  • Pearson will not knowingly direct or send marketing communications to an individual who has expressed a preference not to receive marketing.
  • Where required by applicable law, express or implied consent to marketing exists and has not been withdrawn.

Pearson may provide personal information to a third party service provider on a restricted basis to provide marketing solely on behalf of Pearson or an affiliate or customer for whom Pearson is a service provider. Marketing preferences may be changed at any time.

Correcting/Updating Personal Information


If a user's personally identifiable information changes (such as your postal address or email address), we provide a way to correct or update that user's personal data provided to us. This can be done on the Account page. If a user no longer desires our service and desires to delete his or her account, please contact us at customer-service@informit.com and we will process the deletion of a user's account.

Choice/Opt-out


Users can always make an informed choice as to whether they should proceed with certain services offered by InformIT. If you choose to remove yourself from our mailing list(s) simply visit the following page and uncheck any communication you no longer want to receive: www.informit.com/u.aspx.

Sale of Personal Information


Pearson does not rent or sell personal information in exchange for any payment of money.

While Pearson does not sell personal information, as defined in Nevada law, Nevada residents may email a request for no sale of their personal information to NevadaDesignatedRequest@pearson.com.

Supplemental Privacy Statement for California Residents


California residents should read our Supplemental privacy statement for California residents in conjunction with this Privacy Notice. The Supplemental privacy statement for California residents explains Pearson's commitment to comply with California law and applies to personal information of California residents collected in connection with this site and the Services.

Sharing and Disclosure


Pearson may disclose personal information, as follows:

  • As required by law.
  • With the consent of the individual (or their parent, if the individual is a minor)
  • In response to a subpoena, court order or legal process, to the extent permitted or required by law
  • To protect the security and safety of individuals, data, assets and systems, consistent with applicable law
  • In connection the sale, joint venture or other transfer of some or all of its company or assets, subject to the provisions of this Privacy Notice
  • To investigate or address actual or suspected fraud or other illegal activities
  • To exercise its legal rights, including enforcement of the Terms of Use for this site or another contract
  • To affiliated Pearson companies and other companies and organizations who perform work for Pearson and are obligated to protect the privacy of personal information consistent with this Privacy Notice
  • To a school, organization, company or government agency, where Pearson collects or processes the personal information in a school setting or on behalf of such organization, company or government agency.

Links


This web site contains links to other sites. Please be aware that we are not responsible for the privacy practices of such other sites. We encourage our users to be aware when they leave our site and to read the privacy statements of each and every web site that collects Personal Information. This privacy statement applies solely to information collected by this web site.

Requests and Contact


Please contact us about this Privacy Notice or if you have any requests or questions relating to the privacy of your personal information.

Changes to this Privacy Notice


We may revise this Privacy Notice through an updated posting. We will identify the effective date of the revision in the posting. Often, updates are made to provide greater clarity or to comply with changes in regulatory requirements. If the updates involve material changes to the collection, protection, use or disclosure of Personal Information, Pearson will provide notice of the change through a conspicuous notice on this site or other appropriate way. Continued use of the site after the effective date of a posted revision evidences acceptance. Please contact us if you have questions or concerns about the Privacy Notice or any objection to any revisions.

Last Update: November 17, 2020