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This book is a tutorial on Enterprise JavaBeans (EJB). It's about EJB concepts, tion, which is a PDF file downloadable from weinratgeber.info Each time there is a . Section Now let's make the new enterprise bean (the ejb-jar and the DD ). .. Safari Books Online, LLC. This PDF is exclusively for your use in accordance with the Safari Terms of Service. .. The books in a library stateful stateless. version , is covered by this, the 3rd edition of O'Reilly's EJB book. This 3rd As was mentioned in the Preface, the workbooks can be downloaded in PDF.

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In writing a book about how to use EJB, we had to narrow our audience; nonetheless material [covering the EJB and Java Persistence API (JPA) specs] can be. 1) The intention of this PDF file is to give you free access to preview the book before Also, if you're just starting to learn about EJB, you may want to check out . EJB design strategies into one concise and balanced book. What I “EJB Design Patterns is an excellent book for junior and senior EJB developers alike. EJB.

By separating interface from implementation. It has some very specific algorithms.

The Pricer component implements the IPricer interface. Server-side Component Architectures 9 the component. This data is private to the component. This is possible because the actual implementation is not needed at compile time—only the interface is needed.

And because Java is an in- terpreted language. Enterprise beans are very similar to two other types of Java components: They can be deployed as is. JavaBeans do not need a runtime environment in which to live. You can use JavaBeans to assemble larger-grained components or to build entire applications. Deployable components must be deployed in a container that provides runtime services to the components.

This makes the Java language an ideal technology on which you can base components. Servlets can be deployed in a Web server. The real difference between applets. By way of comparison. Servlets are networked components that you can use to extend the functional- ity of a Web server. Applets can be deployed in a Web page.

JavaBeans do not need a container to instantiate them. Java is an object-oriented language that has been built from the ground-up as a cross-platform develop- ment language and that has wide industry support. Applets are portable Java programs that can be downloaded on the fly and can execute in an untrusting environment.

JavaBeans help you construct larger software that is deployable. You typically do not deploy a JavaBean because a JavaBean is not a complete application. JavaBeans components are small-grained application bits. And because they cannot be deployed. Enterprise beans are larger. Enterprise beans are deployed in an application server. The first one you may have heard of is JavaBeans. The client side could be a Web browser. Both applets and servlets are well suited to handle client-side operations.

This makes servlets ideal for performing Web tasks. Rather than reimplement the wheel. Server-side components need to run in a highly available 24x7. When harnessed properly. EJB is meant for server-side pro- gramming. Professionals who are experts in providing these services write these products. They are meant to perform server-side operations.

You can also provide a user in- terface to your enterprise beans with applets or servlets shown in Figure 1. The server side has different kinds of needs from a rich GUI envi- ronment. You can use JavaBeans as development component building blocks for constructing deployable enterprise beans.

In both these situations. If you choose to home-grow these services Go back to the first page for a quick link to download this book online! Enterprise beans. The client side could also be a Web server. An application server provides this high-end server-side environment for the enterprise beans. Multi-tier Architectures A server-side deployment is software written to support concurrent users per- forming operations simultaneously. A business logic layer contains components that work together to solve busi- ness problems.

Many issues arise. The presentation layer of a Web-based deployment could use Java servlets. Here is a typical layer partitioning: A presentation layer contains components dealing with user interfaces and user interaction.

Note that these layers are purely abstractions. These components could be high-performance engines. A layered system is a well-designed system because each layer is responsible for a sepa- rate task. Server-side Component Architectures 13 yourself. Each layer has a different responsibility in the overall deployment. Being able to outsource server-side services is one of the key benefits of a server- side distributed object architecture like EJB.

Any well-written deployment has a logical software partitioning into layers. Examples of server-side deployments include the following: With so many cli- ents depending on your central server-side deployment.

Java server pages. Combining the Presentation Layer with the Business Logic Layer Your presentation layer and business logic layer can be coupled together in a single tier. In each of these architectures. Central to the data layer is one or more databases that house the stored state.. The physical separation of these layers is another story.

From this debate. In some ways. It should similarly be possible to plug in a dif- ferent set of business rule component implementations within your business logic layer. On the other hand. The advantage to partitioning an application into these logical layers is to iso- late each layer from the others. So what are the advantages to separating your application into two tiers verses N tiers? There are a number of compelling reasons for both sides.

Two-Tier Architectures Traditionally. This draws a tier boundary between the business logic layer and the data layer Figure 1. There are two combinations possible: Two-tier deploy- ments combine the business logic layer with one of the other two layers. And for clarity.

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In the discussion that follows. In a two-tier architec- ture. Database driver switching costs are high. Database drivers must be installed and configured on each of the client tiers. In a two-tier architecture. No database connection pooling between disparate clients Data Layer Database Figure 1. Since Business Logic Components are installed on client.

Since Database Driver is installed on client. This decouples the client from the particular database being used. Client installs are cumbersome and bulky. Two-tier architectures have the following characteristics: Deployment costs are high. If you ever decide to switch between database types such as switching from a rela- tional database to an object database.

Each time your business logic performs a da- tabase operation. Changing the business logic layer involves recompiling and redeploying the client tier. If you ever decide to mi- grate the schema to handle new business processes. By pushing select parts of your logic into stored proce- dures. The fat clients are bound to a da- tabase API. This means that the clients are deal- ing directly with the underlying database schema. This is very costly from a maintenance perspective because the cli- ent tier could reside on the desktops of hundreds or thousands of client ma- chines.

The fat clients directly access the database via JDBC. Business logic migration costs are high. This saves you many round trips. When clients are not using the database. This is illustrated in Figure 1. Network performance suffers. Database type switching costs are high. Database schema switching costs are high. Rather than performing n da- tabase queries.

Database connection costs are high. Every database client needs to estab- lish its own database connection. These connections are limited in number and costly to establish. If this barrier is a network boundary.

Beginning EJB in Java EE 8

It also reduces total network traffic. Network roundtrip latency is reduced for data access. Cost of an IT Department changing to a different database is very expensive. Vendors of Business Logic cannot resell their Tier Boundary code to be used in a different database without significant code changes.

It Go back to the first page for a quick link to download this book online! Stored Procedures Database Figure 1. Business Logic Fulfillment Components may not be Pricing Logic portable components if a Logic proprietary stored procedure language is used. And while the de- velopment of stored procedures is an important step forward. Most of the other problems with two-tiered approaches listed previously. In fact. Now it becomes even harder to plug in a database of a different genre.

It is much cheaper to deploy and configure software in a controlled server-side environment than to deploy Go back to the first page for a quick link to download this book online! It consists of Java servlets. Application servers are necessary to provide a suitable con- tainment environment for the business logic components to run in. Your business logic tier runs within the address space of one or more appli- cation servers.

A three-tiered Web-based deployment is typi- cally broken down as follows: Your presentation tier runs within the address space of one or more Web servers. Database drivers are installed and configured on the server-side. With four or more tiers. The application server is also responsible for making the business components available to be used. In N-tier deployments. Another example is a control system that does not have a graphical user interface.

Yet another example is a distributed deployment that spans company boundaries. Your data tier consists of one or more databases and may contain data-related logic in the form of stored procedures. N-Tier Architectures An N-tier architecture adds one or more tiers to the two-tier model. N-tier architectures have the following characteristics: Deployment costs are low.

A concrete example of an N-tier architecture is a three-tiered Web-based deploy- ment. The application server also manages these components efficiently and provides a number of services to the components.

Java Server Pages. Note that a single-company Web deployment is only one example of a viable N-tier deployment. Another example is a banking system that has many tiers. Tier Boundary. Maintenance of three Driver physical tiers is expensive. Automatic database connection pooling. This enables you to migrate database schemas.

Business logic migration costs are low. Database switching costs are low. Client deployments are thin and simple. Database Figure 1. Business Logic Components are true components. It will run in any database that has a Application Server corresponding driver.

Changing the business logic layer may not necessitate recompiling and redeploying the client tier. Clients no longer access the database di- rectly. Yet the deployment must expose the presentation layer to outside users so that they can hit the Web site. With an N-tier architec- ture. Many businesses are sensitive about protecting their data. A solution is to place a firewall in between the presenta- tion and business logic tiers.

The resulting set of database connections required is often far less than the total number of components in a deployed system. Client Client. Because database connections are very expensive. Rather than your business components acquiring and releasing connections to re- sources such as databases.

The pooling of resources is illustrated in Figure 1. Resource pooling can be applied to other resources as well.

Server-side Component Architectures 21 besides using resources. Each tier can vary independently. Communication performance suffers. Each of these issues is a separate service that needs to be addressed for seri- ous server-side computing. Often times. You are deploying in three or more physically separate tiers.

In a Web deployment.

Software installation costs. Since the tiers are physically separate. For instance. The other tiers can still function properly. This results in high commu- nications overhead. Maintenance costs are high. Making Multi-tier a Reality The benefits of multi-tier deployments do not come for free. Errors are localized.

Only by designing your distributed object application properly can you have an efficient deployment. If a critical error occurs. And each of these services requires a lot of thought and a lot of network middleware plumbing to resolve.

If one tier is overloaded. Appli- cation servers allow you to focus on your application. But unfortunately. This architecture needs to craft a well-formed interface between the ap- plication server.

They provide component developers with common middleware services. Those companies are setting themselves up for failure.

This means that once you bet on an application server. This greatly reduces portability and is an especially tough pill to swal- low in the Java world. Server-side Component Architectures 23 build in-house proprietary frameworks that give some of these services. It also hampers the commerce of components because a customer cannot combine a component written to one application server with another component written to a different application server.

Server-Side Component Architecture Solutions It has been a number of years now since the idea of multi-tier server-side deploy- ments surfaced. Application servers provide a runtime environment for server-side components. The component vendors should be able to focus on the business logic of the problems being solved and not worry about external over- head such as resource pooling.

Why not build instead of download? The application server was born to let you download these middleware services. From this. These interfaces allow the components to be managed in a portable way.

These necessary elements of enterprise-class deployments should be externalized to application server vendors. Since then. Because of this. This will allow components Go back to the first page for a quick link to download this book online! The goal here is rapid application development of server-side de- ployments.

These application servers provide a usable runtime envi- ronment in which components can execute and provide the needed middleware services such as resource pooling and security for reliability and scalability. Note that these technologies are also evolving as we speak— specifically. To address the need. Sun Microsystems. Needs such as resource pooling.

Rather than assembling products from competing vendors. The most popular standards have emerged from Microsoft. This architecture combines the following: Windows NT. We now outline each of these architectures. Distributed COM. Windows NT is scalable to only four processors or reportedly 16 processors with NT 5.

The most notable exception is that J2EE is a specification. This means a Win- dows-based deployment has a very high machine maintenance cost due to the sheer number of machines required. Java is the ideal language. Server-side deployments run in a controlled environment. Sun has produced a complete development platform called the Java 2 Platform. And while the number of server-side Win based workstations is climbing incredibly fast.

This means that customers with legacy applications such as programs written in COBOL on mainframe systems have a well-defined migration path to e-commerce and other modern business processes. Java is also a very convenient language to write server-side components in. This makes it difficult if not impossible to perform deployments on mainframes or high-end UNIX machines.

The mission of J2EE is to provide a platform-independent. The server-side market is dominated by UNIX machines and mainframes. Client-side Java has many problems. But for the server side. J2EE simplifies many of the complexities surrounding the construction of a scalable. Many Java component vendors have been clamoring for a full server- side N-tier story that is Java-based.

This encourages vendors to compete. Vendors such as Inprise. The OMG.

This is definitely a specification to keep an eye on in the future. CORBA is a specification. As we will see in this book. Like J2EE. Because J2EE is a specification meant to address the needs of many companies. For now. We will cover these technologies in Chapter J2EE specifies the rules of engagement that people must agree on when writing enterprise software. This proposal defines the notion of a component in CORBA—an entity that is deployable within an application server.

Poor synchrony between Enterprise APIs. Enterprise API Efforts Sun Microsystems then recognized the power of Java on the server and began to develop several Enterprise APIs that provided enterprise-level services for server-side deployments.

These services include naming and lookup services. These include the following: These appli- cation servers took advantage of the other Enterprise APIs as well.

The early application servers served as a great feedback device to Sun because they highlighted many problems with the Enterprise APIs. The JDK became the de facto reference implementation of the Java plat- form. Enterprise Edition Now that you have seen the three major server-side architectures out there. Sun was not com- municating the typical purpose of the enterprise APIs together as a suite. Sun also be- gan to develop elements of Consumer Java.

Not much exciting development was happening here for server-side middleware support. Why J2EE? To understand why J2EE is necessary. Several months after EJB 1. Enterprise API synchrony. Each platform is a superset of the next smaller platform. Sun has addressed a great deal of the incompatibilities in EJB 1.

When a vendor wrote a product to the EJB 1. Fewer ambiguities. The Java 2 Platform. This is a very restricted form of the Java language due to the inherent performance and capacity limitations of small devices. What versions of each API should be used?

This was unspecified. This platform contains what most people use in standard JDK programming. This specifica- tion corrects bugs and other ambiguities that had been restricting portability. No reference implementation. Sun Microsystems has recently taken a major leap forward in solving the problems we alluded to previously by issuing three different Java platforms.

No way to test application server compatibility. The Enterprise APIs were simply specifica- tions. Sun did not provide a default reference implementation. Sun is providing its own free reference implementation of J2EE. As we mentioned above. RMI allows for interprocess communication and provides other communication-related ser- vices. Server-side Component Architectures 29 This should clear up any confusion about how you can use the Enterprise APIs together to enable a server-side deployment.

Sun is positioning it as a low-end reference platform. If a product passes the tests. JDBC is used in Chapter 8. Sun will issue a compliance brand. JNDI identifies the locations of components or other resources across the network. EJB defines how server-side components are written and provides a standard contract between components and the ap- plication servers that manage them. Enterprise Java is no longer a moving target.

JDBC is a relational database bridge that allows for relatively portable database operations. The technolo- gies included with J2EE are shown in Figure 1. Enterprise Edition is a robust suite of middleware services that make life very easy for server-side application developers. Test suite. Locked-down revisions. EJB promotes the spawning of a compo- nent marketplace.

Sun has fixed this with J2EE. Reference implementation. RMI is covered in Appendix A. Asynchronous Invocations resources. JMS allows for asynchronous distributed object communications. Allows you to perform E-Mail between transaction participants. Enterprise Edition. Other future uses as well Figure 1. Integration with existing systems. Describes EJB components client-side interaction interoperability. Core Java platform language and.

Defines the high-level interface for demarcating transactional Edition boundaries JavaMail.

Beginning EJB in Java EE 8

Provides a unified API for Platform. Defines interfaces between interoperability services. Component Standard. Simple Distributed Standard Edition. Servlets and Java Server Pages.

Provide access to existing enterprise information systems. Scripting capability. CORBA provides language. We do not cover JMS in this book. Provides a namespace for finding components and. We illustrate using servlets with EJB in Chapters 12 and Format for JSP scripts. Typical use is in web server for.

We do not cover JavaMail in this book. Sun Microsystems had not finalized the Java 2 Platform. This barrier to entry will likely result in significant industry consolidation in the Enterprise Java space. J2SE includes the base Java support and the various libraries.

This means that building a J2EE product is an absolutely huge undertaking. Sun expects to complete them by Fall Java IDL allows for integration with other languages. The JavaMail service allows you to send e-mail messages in a plat- form-independent. This means you are likely to see J2EE products emerging in the marketplace sometime in the year It provides complex middleware enterprise features at no cost to application developers.

Java IDL is explained in Chapter Enterprise Edition completely. Enterprise Edition J2EE specifications. To understand more about the real value of J2EE. With EJB. Standard Edition J2SE. Connectors will be included in a future release of J2EE. At the time of this writing May This class provides all the methods we will need throughout the application when accessing the bean.

Java for the Web with Servlets, JSP and EJB PDF

ArrayList; import java. Stateful; import javax. PersistenceContext; import org. BookDao save de. Here is the interface: package de. Page 20 of 47 package de. Entity; import javax. CustomerDao reattach de. CustomerDao findById java. You are a master of DAO objects, now. Stateful Session Bean - business logic I want to recall you the use cases we have.

In order to register the borrow of books, we need to Page 21 of 47 select a customer and books. In fact we have some kind of cart holding the books for the current customer. When we checkout the books are marked as borrowed and the cart is cleaned up.

We will need to get the cart content, as well. Here is our interface. Map; import javax. Map containing the id of the book as key and the book itself as value. Apart from the annotation the content is the same.

You are nearly an EJB 3 expert, so you will manage to set up this interface for yourself. I will continue to our LibraryCart class.

Have a look at it, I will explain some interesting details afterwards. HashMap; import java. List; import java. Map; import java. Set; import javax. Remove; import javax. NamingException; import javax. Logger; import de. BookCartLocal addBook de. BookCartLocal removeBook de. Firstly, we define a Stateful Session bean by adding the annotation Stateful to the class. An entity manager provides all methods needed to insert,update or delete entities or to create queries.

What is EJB stateful Bean?

This was explained in the First EJB 3 tutorial. By adding the annotation PersistenceContext we instruct the container to inject an entity manager to the attribute. To inject means that he initializes the attribute and sets it to a working entity manager.

You may set up a test now, calling your Stateful Session Bean. Web layer Preparing the Struts framework For now your project is still a normal Web project, so we need to add the struts capabilities. Right click on the project and add the capabilities for struts with Add Struts Capabilities.

Change the Base package to de. Page 26 of 47 Notice You can use the libraries and tlds found in the struts-blanc. Download struts from You can find the struts-blank.

It is by far more flexible and powerful.

So we need to add these libraries and the tld files, as well. Your project should look like the following now: Page 27 of 47 If you are not using MyEclipse you must configure your web. Create an index.

Open the struts-config. Click with the right mouse button on the entry action-mappings to create a new action with the wizard. Page 29 of 47 Use the wizard to create a forward action. This is not yet supported by MyEclipse. For non MyEclipse user, here is the struts-config. It is quite simple and does include the navigation. It will contain our navigation reused in all of the JSPs. At the moment, we will only add one navigation option to create sample data for our application.

Quite often this is done using a static string. Try to use static strings rarely as you can, because you can easily make typing mistakes. This is why I define standard variables in a global file. Create a class named Common in the package de. It creates one customer and one book each time it is called. It was not included in the analysis. If you use MyEclipse, create a new action using the wizard. We do not need any FormBean.

Random; import javax. HttpServletRequest; import javax. HttpServletResponse; import org. ActionForm; import org. ActionForward; import org. ActionMapping; import de. If you can find new entries in the database than this part is working fine.

Furthermore, it will allow the library employee to mark books as returned. Use the MyEclipse wizard to create a new DispatchAction with action as parameter. The class provides two methods: unspecified, which is called when no parameter is specified. It tries to get the customer from the current session and loads his borrowed books from the database to show them later in the JSP. The second method returnBook marks a book as returned.

HttpServletResponse; import javax. HttpSession; import org. ActionMapping; import org. ActionMessage; import org. ActionMessages; import org. DispatchAction; import de. He has a unique quality that only a few developers I know have.

Walking into Courts office, I was expecting a typical developer-level conversa- tion, and thats what I received. We turned the design inside and out, marking up my freshly printed hard-copy with scribbles and other unintelligible com- ments that only we could understand.

Finally, satisfied that we had reached a conclusion, I thanked Court and walked toward the door, prepared to implement the changes we had agreed upon. But I didnt make it that far. Court said something to me that would change my way of thinking. He said something that baffled and confused me at first, but would eventually result in a complete paradigm shift and career move for me.

What did Court say? Nothing profound. At first, I had no idea what he was talking about. Enterprise JavaBeans? Whats that? Something like regular JavaBeans? I had no idea. Eventually, Court managed xix Go back to the first page for a quick link to download this book online! And once he explained it, I knew that Trilogy had to do a degree turn, or Trilogy would lose their competitive advantage. You see, EJB is a specification for a server-side component marketplace.

EJB enables you to download off-the-shelf components from one vendor, combine them with components from another vendor, and run those components in an application server written by yet a third vendor. This means companies could collaborate on the server-side. EJB enables you to download, rather than build, ele- ments of server-side applications. The EJB value proposition had strong ramifications for Trilogy. EJB represented a way for Trilogy to get out of this middleware business, and concentrate on their e-commerce strategic efforts.

This would mean discarding the backbone com- pletely in favor of a third party vendors architecture. Not only would this re- duce Trilogys maintenance costs, but it would solidify their software suite, since their middleware would now be written by professionals who had been in the business for twenty years. This proposition would eventually lead to an entirely new business unit forming at Trilogy.

Back then, the specification was about a third of the size its grown to today. Understanding the specification turned out to be much more challenging than downloading it. The specification was written for system-level vendors, and was not meant to be a tutorial for end developers. The section on entity beans, for example, took me a good two months to really grasp, as the notion of persis- tent components was new to me.

This arduous struggle with understanding the EJB specification is what even- tually lead me to write this book for you. This book represents everything I wish I had when I first started a year and a half ago. So what is this book about? This is not a book on EJB propaganda. Well, it may be more accurate to tell you what this book is not about. This is not a book on how to write EJB code on any single application server. This is not a nice book that paints a perfect picture of the EJB world.

This is not an advertisement for any particular EJB product, nor a campaign to rid the world of Microsoft. The goal of this book is to help you.

I want you to be able to craft solid, secure, and scalable server-side deployments.EJB defines a set of strict interfaces and guidelines that must be followed or the entire model will break down. As EJB matures. JavaBeans do not need a runtime environment in which to live. ActionMapping; import org. Login Forgot your password?

Enterprise API Efforts Sun Microsystems then recognized the power of Java on the server and began to develop several Enterprise APIs that provided enterprise-level services for server-side deployments. Dev Ops Agenda How to bust security silos and secure your operation DevOps means velocity, though, not at security's expense. The class provides two methods: unspecified, which is called when no parameter is specified.

Entity beans are very useful when you have a legacy database with data already inside.

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