- The EJB Runtime Environment
- Installing an Application Server and Deploying EJBs into It
- Divide and Conquer
- The Rest of the Story: Deploying EJBs
The Rest of the Story: Deploying EJBs
The code for Book is now complete. Alas, the coding work represents only half of the effort needed to deliver a working Entity Bean. Book won't be ready to use until you deploy it to the container.
Traditionally, Java classes' behaviors have been manifested exclusively through Java code; if you wanted a class such as Book to exhibit a certain behavior, you had to write Java code to provide it. Java programmers were, if not happy about all the code they had to write, at least resigned to that way of life because nobody realized there was another way to implement classes.
Somebody (or, more likely, some committee) eventually started examining the hundreds of thousands of lines of Java code running businesses around the globe. These people (I'll refer to them as the ubiquitous "they") noted striking patterns permeating much of the existing Java code. Specifically, they noticed that most Java classes included code to do the following:
Make themselves visible on a network, via some low-level protocol such as RMI or sockets.
Associate themselves with a database by using java.sql.DriverManager and java.sql.Connection.
Wrap database operations in transactions.
Perform database selects, updates, inserts, and deletes.
These common operations, although conceptually simple, are cumbersome and tiresome to implement directly in Java, which makes them particularly vulnerable to logic errors; when I am writing the same boring, repetitive code snippets over and over, my coding tends to get sloppy and error-filled, and I suspect that other developers suffer the same fate. Furthermore, errors in these "easy" sections of Java code tend to be hard to find because developers are so familiar with the nature of the code that they fail to read it carefully when searching for bugs.
Another problem with the more mundane portions of Java classes is that they tend to depend on their environmental context. Take database access code, for example. Many developers create and test their code using a "test" database, and then deploy the code to an environment where it has to use a "production" database. "Pointing" the code to the production database is admittedly a small, simple change, but it often fails to occur, thereby causing a production system to use a test database. Myriad bits of information such as this are unnecessarily "baked into" Java code, so they make the code highly brittle; otherwise insignificant changes to a Java class's environment cause the class to fail to work properly.
EJB's creators noted these two aspects of Java code (lots of repetitive code and "baked in" dependencies on the environment) and decided to do something about it. They decided to factor these two aspects of Java class implementations out of Java code and into a set of XML files called a deployment descriptor. Deployment descriptors solve a wide range of commonly occurring Java problems, most notably:
They replace large swaths of repetitive and error-prone Java code with simple XML-based constructs.
They house a majority of environmental information that would otherwise be baked into Java code, thereby making Java classes more responsive to changes in the environment.
A deployment descriptor accompanies every Enterprise JavaBean. It contains a wealth of information on the Bean's methods, the Bean's relationships with other Beans, and the Bean's relationships with and dependencies on its runtime environment. Deployment descriptors are generally spread among several XML files; the exact set of files in a given descriptor is determined by the Bean's type (Entity, Session, Message-Driven) and by the vendor of the EJB application server into which the Bean is deployed.
Deployment descriptors solve many of the problems common in enterprise Java development. However, in some ways they just replace the old set of problems with a whole new conundrum. Deployment descriptors vary greatly from one application server to another, so they are not portable; a deployment descriptor for deploying an EJB to WebLogic, for example, does not work with Sun's Reference Server. Furthermore, deployment descriptors are heavily laden with their own complicated syntax and semantics, making them almost as error prone as the Java code they are meant to replace.
That's the bad news. Now here's the good news: Utility programs, commonly called "deployment tools," are available that can actually generate deployment descriptors for you. These tools, although not perfect, perform admirably enough that they largely eradicate the burden of creating deployment descriptors by hand.
Sun's Reference Server is bundled with a handy deployment tool named, simply enough, deploytool. With deploytool, the Book EJB can be deployed quickly to the Sun Reference Server.
Using deploytool to Deploy Book
The deploytool utility can be used as a GUI or a command-line tool. I am normally a command-line kind of guy, but deploytool's GUI version is so easy to use that I heartily recommend it for everyday use. It cannot operate properly unless the Reference Server is running, so please make sure you have started it per the instructions in Appendix B. After the server is running, type the following command to start deploytool:
Step 1: Create an Application
After a moment, deploytool's GUI dialog box occupies a niche of your screen. The standard unit of code in deploytool is an application, which is, for the purposes of this tutorial, merely a collection of deployable EJBs. Deploytool insists that all EJBs belong to an application, so your first task is to create a new application. Using deploytool's File, New, Application command, create a new application. In the Application File Name text box, enter BookEazAdmin, enter BookEaz Administrative Utilities in the Application Display Name text box, and then click OK (see Figure 3.3).Figure 3.3 Applications are the basic unit of work in Sun's Reference Server.
Step 2: Create the Book EJB
Use deploytool's File, New, Enterprise Bean menu command to start the New Enterprise Bean Wizard. Like most wizards, it conducts an interview in which you describe the details of the EJB you are deploying. After completing the interview, the wizard creates a deployable JAR file and a semantically complete deployment descriptor.
Use the following settings in the wizard's first window:
Click the Create New JAR File in Application radio button.
In the JAR Display Name text box, enter BookEJB Jar, as shown in Figure 3.4. The display name is the name by which this EJB's JAR file will be known in deploytool's browser.
Click the Edit button near the Contents section to add Book's compiled class files into the JAR being built.
Navigate to c:\Bookeaz\classes\com\bookeaz\books in the Available Files section of the dialog box. Highlight Book.class, BookBean.class, and BookHome.class, and then click the Add button. This informs the wizard that the three selected files are to be added to the JAR file being built.
Click the Next button to signal the completion of the first window.
Perform the following actions in the second window, shown in Figure 3.5:
Click the Entity radio button in the Bean Type section.
In the Enterprise Bean Class list box, select com.bookeaz.books.BookBean.
Enter BookBean in the Enterprise Bean Name text box.
Select com.bookeaz.books.BookHome in the Remote Home Interface list box.
In the Remote Interface list box, select com.bookeaz.books.Book.
Click the Next button to signal the completion of the second window.
Perform the following actions in the third window:
Click the Container Managed Persistence (2.0) radio button.
Place a check mark next to every field in the Fields To Be Persisted section.
In the Abstract Schema Name text box, enter Books.
Enter java.lang.String in the Primary Key Class text box.
Select iSBNNumber in the Primary Key Field Name list box (the first letter of iSBNNumber is intentionally lowercase to conform to the JavaBean pattern for naming attributes).
Click the Finder/Select Methods button to describe the findByTitle, findByAuthor, and findBySubject methods to the wizard.
Click on findByAuthor in the Method list (see Figure 3.6).
Enter SELECT Object(b) from Books as b where b.author = ?1 into the EJB-QL Query for findByAuthor text box.
Click on findBySubject in the Method list.
Enter SELECT Object(b) from Books as b where b.subject = ?1 into the EJB-QL Query for findBySubject text box.
Click on findByTitle in the Method list.
Enter SELECT Object(b) from Books as b where b.title = ?1 into the EJB-QL Query for findByTitle text box.
Click the Finish button to indicate that you are done building the deployment descriptor.
Running the wizard produces a deployable JAR named Book EJB Jar that's added to the BookEaz Administrative Utilities application. There is just one more quick step to complete, and then the Book EJB will actually be deployed!
The final step involves mapping the Book EJB to a database. Here's how you do it:
Highlight BookBean's coffee bean icon in the browser portion (upper-left pane) of deploytool's main window.
Click the Entity tab in the main pane of the deploytool window.
Click the Deployment Settings button to open the Deployment Settings dialog box.
Click the Database Settings button.
Enter jdbc/BooksInCloudscape into the Database JNDI Name text box (see Figure 3.7).
Click the Generate SQL Now button.
Click the OK button, and then click the OK button again to close the Deployment Settings dialog box.
Those last few actions put Book into a completely deployable state, so it makes sense to actually deploy it and start testing it. Follow these steps to deploy Book and make it ready for testing:
Choose the Tools, Deploy menu command in deploytool's main window to open the Deploy BookEaz Administrative UtilitiesIntroduction dialog box.
Click the Return Client Jar button.
Click the Next button.
Enter BookBean into the JNDI Name column of the Application section.
Click the Finish button.
Congratulations! You have just deployed your first Entity Bean. Book is now ready to participate in UC6. All you need now is a client program to interact with the Entity Bean.
BookEaz's Database Administrator Client
Book is now deployed to the application server and patiently awaiting a client program to use its book-manipulation services. BookAdministrator is a small-but-useful client program that collaborates with the Book EJB to provide the behavior mandated in UC6; it has facilities for performing bulk updates of the Book inventory.
BookAdministrator looks like most client programs that use EJBs. Like all its EJB-using brethren, it performs these tasks:
It establishes contact with the EJB container by acquiring an object called an InitialContext:
//establish contact with the Book Entity Bean //via the wonders of Java naming (JNDI) //this is how you obtain a home when you are NOT //running in the same JVM as the EJB Properties h = new Properties(); h.put(Context.INITIAL_CONTEXT_FACTORY, "com.sun.enterprise.naming.SerialInitContextFactory"); h.put(Context.PROVIDER_URL, url); InitialContext ctx = new InitialContext(h);
It uses the InitialContext object to establish contact with BookHome:
//The InitialContext is your conduit for getting //a BookHome Object rawHome = ctx.lookup("BookHome"); //you have to cast rawHome to a "real" BookHome in a safe way return (BookHome) PortableRemoteObject.narrow(rawHome,BookHome.class);
It uses BookHome to perform database operations on Books, such as finding existing Books:
Book bk = home.findByPrimaryKey(tk);
and creating new Books:
BookAdministrator's code is as notable for what it lacks as for what it contains. Like all client code that uses EJBs, BookAdministrator lacks code to do the following:
Establish connections to databases.
Start, commit, or roll back transactions.
Marshal remote method invocations.
Explicitly perform database queries, updates, inserts, or deletes.
In short, by virtue of the work you performed to make Book an EJB, programs such as BookAdministrator become concise (far fewer lines of code than traditional J2SE clients) and portable (no dependencies on JDBC or a specific database implementation) .
Compiling and Running BookAdministrator
BookAdministrator's source code is available for download at the companion Web site; it is included in the same archive as Book's source code, so you have probably already copied it to your computer. If not, follow the directions at the beginning of this chapter to download the source code and place it into <BOOKEAZ_HOME>.
Compiling BookAdministrator is relatively easy:
Open a command-prompt window.
Change the directory to <BOOKEAZ_HOME>\src\com\bookeaz\admin.
Compile BookAdministrator and its accompanying exception classes by issuing this command:
javac d c:\bookeaz\classes *.java
Running BookAdministrator is scarcely more difficult than compiling it. The only oddity in the process is that a new JAR file must be added to CLASSPATH for BookAdministrator to work properly. This new JAR file, named bookEazAdminClient.jar, was generated by deploytool when it deployed Book to the EJB container. The JAR file contains a few stub classes that help clients interact with the Book EJB.
Follow these steps to run BookAdministrator:
Add <BOOKEAZ_HOME>\bookEazAdminClient.jar to CLASSPATH by issuing the following command (substituting in your actual value of <BOOKEAZ_HOME>):
Change the directory to c:\bookeaz.
Start BookAdministrator with this command:
java com.bookeaz.admin.BookAdministrator books.dat
You just used BookAdministrator to establish BookEaz's initial inventory of Books! I normally refrain from using exclamation points (they ruin my façade of stoicism), but I felt it necessary to make an exception here because you have just used your first Entity Bean to accomplish a real task.
Go ahead and run BookAdministrator as many times as you want, so that you can bask in the glory of your programming prowess; I just ran it about a dozen times in a row to assure myself that it really does work.