104 WebSphere Studio Application Developer Version 5 Programming Guide Executing the CustomerListing class should result in an error. The Console view will display the following error message: Customer Listing for CUSTOMER Exception: COM.ibm.db2.jdbc.app.DB2Driver Exception: null The exception information indicates that there was a problem locating a class required to run the program. To correct the error you have to add the JAR file with the DB2 JDBC driver code to the classpath. Adding a JAR file to the classpath We have to update the Java build path that was previously defined. Select the ItsoProGuideJava project and Properties from the context menu. Then you select the Java Build Path entry and the Libraries tab (Figure 5-12). Figure 5-12 Java Build Path settings for the ItsoProGuideJava project There are two ways you can specify access to the required classes:  Select Add External JARs and locate the db2java.zip file in the file system.  Select Add Variable to add a variable that refers to the db2java.zip file. It is recommended to use the second option because you are not directly referencing a physical path that could be different for another developer within a team. Chapter 5. Developing Java applications 105 For this sample it is assumed that a variable DB2JAVA has been defined. If DB2 is installed on your system, Application Developer predefines this variable. To add this variable to the Java build path for the project, select Add Variable to display the New Variable Classpath Entry dialog (Figure 5-13). Figure 5-13 Adding a variable to the classpath Select the DB2JAVA variable and close the dialog with OK . If the DB2JAVA variable is not available in the dialog, you have to create a new variable. Click the New button to display the New Variable Entry dialog (Figure 5-14). Enter DB2JAVA in the name field and select the file db2java.zip from the file system by clicking the File button and confirm the dialog with OK . Figure 5-14 New Variable Entry dialog The sample code can now be executed again and the list of customers in the database table should be displayed in the Console view. Note: The EJBBANK database must be defined for this example. See “Installing the EJBBANK database” on page 811 for instructions. DB2JAVA c:\sqllib\java\db2java.zip 106 WebSphere Studio Application Developer Version 5 Programming Guide Exporting code and running outside Application Developer If you would like to run this sample application outside of Application Developer you can export the class file to the file system and run it from there:  Select File -> Export . The Export dialog is displayed (Figure 5-15). Figure 5-15 Export dialog  This dialog allows you to select the destination of the export. In this example we will do a simple export to the file system. If the code would have been in several class files, or if there would have been other resources required to run the program, you could have chosen to export the sample project as a JAR file instead. When you have made your selection—in this case select File system —click Next to specify the resources to export (Figure 5-16). Chapter 5. Developing Java applications 107 Figure 5-16 Export to File System dialog  Expand the project which is shown in the left pane and select the CustomerListing.class file in the right pane. You can specify the directory where you would like to export the file. In this example we use C:\ as the path and check the Create directory structure for files check box. This option creates the directory path ItsoProGuideJava\itso\java for the file.  To run the application, open a command prompt window, switch to the ItsoProGuideJava directory and enter the command: java -cp ".;c:\sqllib\java\db2java.zip" itso.java.CustomerListing The db2java.zip file is already added to the classpath after DB2 has been installed. Therefore the following command should also execute the sample application: java itso.java.CustomerListing  After running this program, the customer list is displayed in the command window. 108 WebSphere Studio Application Developer Version 5 Programming Guide Locating compile errors in your code All compile errors in your Java code are shown in the Tasks view. An example of such an entry in the CustomerListings.java file is displayed in Figure 5-17. The entry in the Tasks view is marked with this symbol . Double-clicking the entry in the task list will navigate to the line in the source editor, where the error was detected. The line where the error occurs is also indicated by a yellow light bulb. If you move the mouse over the light bulb, the error message is shown. Figure 5-17 Identifying errors in Java code To more easily find the errors in the file you are working in, you can filter the Tasks view to only show errors related to the current resource. To do this, click the Filter icon in the Tasks view and select the entry On selected resource only (or On any resource in same project ) in the Filter Tasks dialog (Figure 5-18). Note: The command may be different on your system, depending on where DB2 has been installed. You also need to ensure that the file java.exe is accessible in the path. In the Application Developer installation folder you will find a copy of java.exe located in the <wsadhome>\eclipse\jre\bin directory. Chapter 5. Developing Java applications 109 Figure 5-18 Filter Tasks dialog Debugging your code How to debug Java applications in Application Developer is described in detail in Chapter 16, “Testing and debugging” on page 553. In this section we will only take a quick look at how to debug the simple Java application we have just created. Setting a breakpoint in a method causes the Debug perspective to open. A breakpoint is a temporary marker in your code to tell the debugger to suspend executing your program at a given point. To set a breakpoint in the code, double-click in the grey area left of the statement in the Java editor where you want to set the breakpoint. You can also open the context menu and select Add Breakpoint (Figure 5-19). Typical setting: resources in the same project 110 WebSphere Studio Application Developer Version 5 Programming Guide If you want to see all breakpoints that are currently set, select Window -> Show View -> Other and select the Breakpoints view located in the Debug tree. Figure 5-19 Setting a breakpoint To debug the CustomerListing class, you can start the program in debug mode by clicking the Debug icon in the toolbar . This opens the Debug perspective and run the program until the first breakpoint has been reached. Within the Debug perspective you can view, inspect, and modify variables, and can trace your code (Figure 5-20). Figure 5-20 Debug perspective Step through the code Watch the variables Breakpoint Chapter 5. Developing Java applications 111  Step through the code line by line using the icon in the toolbar of the Debug view. Other icons let you step into methods, or step to the return of a method.  Watch the variable values in the Variables view.  Run the program to the end using the icon.  Close the Debug perspective and any open editors. Preparing a utility project Utility projects are Java projects containing code that should be available to multiple modules of an enterprise application. J2EE 1.3 provides support for utility JAR files at the enterprise application level. Such JAR files are then made available to Web and EJB modules as JAR file dependencies. Banking model Later in this book, when we implement an enterprise application with a Web module in Chapter 7, “Developing Web applications” on page 179, we will use a banking model that we define in the Java project. Figure 5-21 shows the types used in the banking model. Figure 5-21 Banking model TransRecord Customer Account Banking Test Façade Business Model Bank 1:m Customer JSP Servlet Front-end 1:m m:m 1:m 112 WebSphere Studio Application Developer Version 5 Programming Guide Customer A customer of the bank. Account A bank account. A customer may have multiple bank accounts and an account may be owned by multiple customers. TransRecord A transaction record that is generated for each banking transaction, such as a deposit, withdrawal, or transfer of money between two accounts. A bank account may have many transaction records. Bank The mediator. Mediators act as coordinators, encapsulating the other objects and how they interact. The bank class holds the customer, account, and transaction record objects, and methods to work with them. In Chapter 12, “Developing EJB applications” on page 373 we replace the Bank class with a EJB session bean that provides the same functions. The session bean interacts with entity beans that map to relational tables. BankingTest The facade. The intent of facades is to provide a simple and unified interface to the otherwise complex model that lies behind it. By doing so, we reduce the dependencies between the model classes and its clients. Less dependencies mean more freedom to adapt to new requirements. The BankingTest facade is for testing purposes only. We will implement the real facade in the front-end modules, for example, in Web applications. Design considerations This design with separation of front-end and backend enables us to implement multiple front-ends and multiple business models that work with each other.  In Chapter 7, “Developing Web applications” on page 179, we implement a front-end Web application using basic servlets and JSPs.  In Chapter 10, “Developing Struts applications” on page 293, we implement a front-end Web application using the Struts framework.  In Chapter 12, “Developing EJB applications” on page 373, we implement the business model as enterprise beans (EJBs). With a small change to the facade bean we can then run both Web applications against the EJB business model. Note: Both mediator and facade are documented design patterns. Refer to Design Patterns: Elements of Reusable Object-Oriented Softwar e. Chapter 5. Developing Java applications 113 Implementation We use an implementation in regular JavaBeans with data in memory for the model. Additional services like persistence, distribution, security, or transaction management were not considered. We wanted to keep the model layer as simple as possible, not to add to the complexity natural to this kind of application. However, we can redesign the model with the use of an underlying database at any time. Packages and classes The model is implemented in these packages and classes: itso.bank.model Model classes: Bank, Customer, Account, TransRecord Customer: id, title, firstname, lastname Account: id, balance, type TransRecord: timeStamp, transType, transAmt itso.bank.facade The facade for banking operations is the BankingTest class. This is the initial implementation of the facade. itso.bank.exception Application exceptions: AccountDoesNotExistException, CustomerDoesNotExistException, ZeroAmountException, InvalidAmountException, BankException, InsufficientFundsException itso.bank.util Converter of amounts between numeric and character representations: AmountConverter itso.bank.main Test program: BankMain The Bank class initializes the data in memory. Instances of customers and accounts are kept as java.util.Map. The customer-account relationship is held as a java.util.Vector for each customer within a java.util.Map. The transaction records of an account are held as a java.util.TreeSet for each Account within a java.util.Map. All amounts are kept as java.math.BigDecimal, which provide accurate calculations of amounts. Business logic All classes provide getter and setter methods for the attributes. To work with the model the following business logic methods are provided:  The Customer class provides no special methods.  The Account class provides deposit and withdraw methods to perform banking transactions. . instructions. DB2JAVA c:sqllibjavadb2java.zip 106 WebSphere Studio Application Developer Version 5 Programming Guide Exporting code and running outside Application Developer If you would like to run this sample application outside of Application. and select Add Breakpoint (Figure 5- 19). Typical setting: resources in the same project 110 WebSphere Studio Application Developer Version 5 Programming Guide If you want to see all breakpoints. sample application: java itso.java.CustomerListing  After running this program, the customer list is displayed in the command window. 108 WebSphere Studio Application Developer Version 5 Programming