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Tutorial for building J2EE Applications using JBOSS and ECLIPSE (5)

作者:未知 来源:月光软件站 加入时间:2005-6-5 月光软件站

Chapter 5.

Creating a BMP Entity Bean

This chapter describes how to create a Bean Managed Persistence (BMP) EJB component. We will create two BMP beans, Customer and Manager, as shown below. The Customer bean will be responsible for storing the details of customers of MyStore. The Manager bean stores details of the manager of MyStore. Both beans communicate with their respective tables in the database using Data Access Objects (DAOs) named CustomerDAO and ManagerDAO respectively.

All customers have been assigned a unique customerID for housekeeping purposes in MyStore in addition to their username for accessing the services of MyStore. Similarly the Manager of MyStore has been assigned a unique ManagerID.

Note : It is the usual practice to access business methods of BMP beans via a session bean, which encapsulates business logic and acts as an interface to further EJB components. In this case Customer and Manager are accessible via by StoreAccess.

This approach comes from a pattern called a Session Facade, whereby enterprise beans encapsulate business logic and business data and expose their interfaces. The session bean acts as a facade to encapsulate the complexity of interactions with the lower-level beans. The session facade is responsible for managing business objects and provides a uniform business service abstraction to presentation layer clients, thereby hiding the business object implementation in the lower-level beans.

This tutorial uses that pattern for business tier implementation.

Tasks :

  1. Create a BMP bean named Customer under package

  2. Create a DAO class named CustomerDAOImpl under package

  3. Add all attributes/properties to the CustomerBean, with getter and setter methods for each of the attributes.

  4. Add a finder method named ejbFindByPrimaryKey with the signature

    public CustomerPK ejbFindByPrimaryKey (CustomerPK pk) throws FinderException

  5. Add a finder method named ejbFindByUserID with the signature

    public CustomerPK ejbFindByUserID (String userID) throws FinderException

  6. Add a business method named getCustomerData with the signature

    public CustomerData getCustomerData()

  7. Implement required methods in the CustomerDAOImpl class.

  8. Deploy the Customer Bean.

  9. Add a create method to the StoreAccess Bean.

    public void ejbCreate() throws javax.ejb.CreateException

  10. Add a business method to the StoreAccess Bean.

    public CustomerData getCustomerData(String userID)

  11. Create a test client named SessionBMPClient under package

  12. Run your client and test the bean.

Create the Customer BMP Entity Bean :

Go To Package Explorer > Expand Mystore (project) node > select src, right click and a menu will pop up.

On the pop up menu > New > Lomboz EJB Creation Wizard.

Enter package name, bean name Customer and select bean type as Bean Manged Entity > Finish.

This will create a package named under src and CustomerBean under that package as shown below.

Note: It will generate the bean name, jndi-name and type of bean in file. Also, the word 'Bean' is appended to the name of the file.

As we can see from the figure above it has created a class level tag @ejb.bean, which has assigned the bean type, its name and its JNDI name which will be generated in the Home interface. This tag will also generate deployment descriptors in ejb-jar.xml and jboss.xml file once you generate your EJB classes.

Now we are going to generate all the interfaces including Home, Remote, DAO and other helper classes. We don't need to specify any tags in ejbGenerate.xml as we have already set up that for the MyStoreMgr EJB module in chapter 3.

Go to node CustomerBean under > LombozJ2EE > Add EJB to Module > Select MyStoreMgr > Ok.

Go to MyStoreMgr node > LombozJ2EE > Generate EJB classes.

Note: All these steps are covered in previous chapters (chapter 3 and 1) so please refer to those sections if you need further details.

Now let's see what files are generated by Xdoclet.

As shown below there are two new files named CustomerData and CustomerPK in addition to what we had for our session beans. We also have a CustomerBMP which extends our CustomerBean class. The remaining files should be familiar from our work with session beans.

As discussed in chapter 3 regading the various ejbDoclet tags used in ejbGenerate.xml, to generate these classes, CustomerData and CutomerPk are generated by following tags as shown below in this snippet from ejbGenerate.xml:

The relevant tags are <dataobject/> and <entitypk/>.

Note: There is no CustomerDAO class, as we haven't generated that file by specifying the dao tag in the CustomerBean class.

Create Customer's DAO Interface :

Since we are going to use a DAO to access database for this bean, we have to create a DAOImpl class to provide an implementation for the generated DAO interface.

Go to src > package > Add a class