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Use Eclipse Oxygen and WebSphere Liberty for rapid JPA Enterprise development

Rapidly generate Java Persistence Architecture beans for an enterprise application

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Java™ Persistence API (JPA) entities simplify Java persistence by using an object-relational mapping approach to define how to map Java objects to relational database tables in a standard way. In this tutorial, learn how to create JPA entities using Eclipse Oxygen, IBM WebSphere® Liberty 17, and Apache Derby 10. I give you step-by-step instructions on how to build the JPA-based Acme Membership application.

This tutorial focuses on how to create JPA entities that meet the following requirements:

  • They are generated from pre-existing relational tables. This is sometimes referred to as a "bottom-up" approach.
  • They use database-generated primary key values for the ID attribute.
  • They are part of a composition (or aggregation) of one or more other JPA entity beans (for example, one-to-one or many-to-one relationships).

You will learn how to construct an application that uses an Enterprise JavaBean (EJB) 3.1 stateless session bean and a servlet at the Servlet 2.5 specification level to invoke a JPA transaction. Using JPA beans, you will build a simple web application, Acme Membership, without writing much code. Acme Gym Membership is a fictional health gym membership application to manage members of the Acme Gym.

Before you start

To follow along, you need to install the following:

  • Eclipse IDE for Java EE Developers, Oxygen Release 4.7 development environment with Java Development Kit (JDK) 8 Update 131 or later
  • Apache Derby Network Server V10.13.1.1
  • Liberty Tools for Eclipse Oxygen
  • IBM WebSphere Application Server Liberty 17.0.0.2 (targeting the Java Enterprise Edition 7.0 specification)

Extract the resources.zip file from GitHub to a location of your choice in your file system. It contains two files: members.sql and AcmeMembershipApplication.ear. These resources include a script to create your initial Derby database and an Enterprise Archive (EAR) file that contains artifacts to begin developing your Java Enterprise Edition (JEE) application.

The Acme Gym membership scenario

To receive Acme's gym services and benefits, clients must become members. The membership_type field in the membership table identifies the type of membership.

Clients can choose from single, student, or family memberships. Family memberships provide Acme's services to couples and any children that they have who are under the age of 18.

All memberships will have, at most, one primary member. The primary member is responsible for keeping the membership in good standing and for paying the annual subscription fees. All correspondence between Acme and its members occurs solely through the primary member. Acme collects the address and other contact information for the primary member for all memberships for this purpose.

In addition to having a primary member, a family membership normally has one or more dependents. There are two types of dependents in a family membership: the spouse and any children younger than 18.

To remain members in "good standing," clients must renew their memberships annually.

Figure 1 represents the relational database schema for Acme's membership subsystem.

Figure 1. The Acme membership data model
Diagram shows five tables for            Acme's membership database
Diagram shows five tables for Acme's membership database

Import the membership application

Now that you understand the scenario, let's look at how to import the membership application into your own environment.

  1. Launch Eclipse and open the web perspective.
  2. Import the initial WAR project that you will build upon:
    1. From the menu bar, select File > Import.
    2. Expand the Web folder, select WAR file and click Next.
    3. In the WAR Import wizard, click Browse, navigate to the location where you downloaded and saved the file AcmeMembershipApplicationWeb.war to and select it for import.
    4. Uncheck the Add project to an EAR and select WebSphere Application Server Liberty for Target runtime
    5. Click Finish.

Upon successful import, you will see errors in the Markers view that you can safely ignore for now. The new web project has a simple servlet that uses a stateless session EJB to invoke the JPA entities you will create to add members and memberships.

Create the Acme membership database

Acme's membership application depends on the existing layout of the Acme database. You will recreate Acme's membership database tables using the Derby Network Server database.

  1. Open the Data Development perspective.
  2. In the Data Source Explorer view, right-click the Database Connections folder and select New, and the New Connection Profile wizard will appear.
  3. Select Derby from the list of choices in the Connection Profile Types panel and enter AcmeMembers for name.
  4. Click Next.
  5. On the Specify a Driver and Connection Details page:
    1. Select the checkboxes next to Connect when the wizard completes and Connect every time the workbench is started .
    2. Click the New Driver Definition icon, as shown below.
      Figure 2. Configuring a new Derby connection
      Image shows establishing a connection to the AcmeMembers Derby database
      Image shows establishing a connection to the AcmeMembers Derby database
    3. The New Driver Definition wizard opens. In the name/type tab of this wizard, select Derby Client JDBC driver with a System Version of 10.2.
    4. Click the JAR list tab and the derbyclient.jar entry in the Driver files panel, then click the Edit JAR/Zip button, as shown below.
      Figure 3. Linking the Derby library to the new connection
      Image shows selecting the Derby client library location for the new database connection
      Image shows selecting the Derby client library location for the new database connection
    5. Navigate to the installation direction of your local Derby network server, and under the lib directory of your root Derby installation, select the derbyclient.jar, indicating its location, and click OK.
    6. You are now back in the New Derby Connection Profile wizard. On the Properties tab, enter ACMEMEMBERS for database name. You can also optionally change the user ID and password values from the defaults. Check the Create database (if required), Upgrade database to current version, and the Save password checkboxes, as shown below.
    7. Click Test Connection. Click OK on the Ping Succeeded notification pop-up dialog.
    8. Click Finish.
      Figure 4. Specifying database connection details
      Image shows specifying Acme's membership database connection details
      Image shows specifying Acme's membership database connection details
  6. Return to the web perspective and in the Enterprise Explorer view, expand AcmeMembershipApplicationWeb > WebContent and open Members.sql.
    1. Select Derby_10.x from the type drop-down list.
    2. Select AcmeMembers from the name drop-down list.
    3. Select ACMEMEMBERS from the database drop-down list.
      Figure 5. Preparing script to create Acme membership database
      Image shows preparing the            connection profile details to run script to create membership database
      Image shows preparing the connection profile details to run script to create membership database
    4. Save the changes.
    5. Right-click anywhere in the open editor and select Execute All.
    6. The SQL Results view will open and show a success message.

If you switch to the Data perspective and from the Data Source Explorer, navigate to Database Connections > AcmeMembers > ACMEMEMBERS > Schemas > ADMIN > Tables, you will notice the creation of the new tables from executing the Members.sql script.

Use the identity value generation strategy

Having the database generate values for the primary key for a table (and by extension, any foreign key values for related tables) eliminates the burden from the application to do so. That is, not having to generate unique key values for persistent objects within the application allows the focus to remain on core business logic and business rules. This enhances the application's maintainability and readability.

In this scenario, Acme's lead data and application architects want to use the identity value generation approach to remove that burden from the business logic of their various applications. To leverage that capability, JPA can delegate assignment of an entity's ID attribute to the relational database. The primary key fields in the relational tables for the ACMEMEMBERS database are set to generate unique values to adhere to the identity value generation strategy.

Generate the JPA entities

Now it's time to generate the JPA entities from the ACMEMEMBERS database tables. These JPA entities provide the foundation of the business logic for Acme's membership system. Switch to the web perspective and enable the JPA facet for our web project.

  1. Right-click the AcmeMembershipApplicationWeb project and select Properties.
  2. Select Project Facets from the list of project properties in the left-most pane.
  3. In the list of available Project Facets in the center pane, select JPA and ensure that the version is set to 2.1, as shown below.
  4. Click Further configuration available near the bottom of the center pane.
    Figure 6. Enabling JPA for the AcmeMembersWebApplication
    Image shows enabling the JPA            facet for the Acme membership web application
    Image shows enabling the JPA facet for the Acme membership web application
  5. In the JPA Facet dialog wizard:
    1. Select EclipseLink 2.5.x from the platform drop-down list.
    2. Select Library Provided by Target Runtime from the type drop-down list.
    3. Select AcmeMembers from the connection drop-down list, as shown below.
    4. Click OK.
    5. Click Apply and Close on the properties dialog window.
    Figure 7. Providing runtime details to enable JPA
    Image shows providing runtime details to enable JPA
    Image shows providing runtime details to enable JPA

    After configuring your web project to support JPA, you can generate your JPA entities:
  6. Right-click the AcmeMembershipApplicationWeb project and select JPA Tools > Generate Entities from Tables.
  7. On the Select Tables page of the Generate Custom Entities wizard:
    1. Select AcmeMembers from the connection drop-down list.
    2. Select ADMIN from the schema drop-down list.
    3. Be sure to check all tables listed in the tables list.
    4. Check the List generated classes in persistence.xml checkbox.
    5. Click Next.
    6. On the Table Associations page of the Generate Custom Entities wizard, you have an opportunity to generate and shape relationships between the entities you will generate.
      1. Select the Dependent-Membership relationship and ensure both Cascade fields are set to all, and enter membership for the Property field.

        In the screen shown below, you are setting the name of the attribute that provides the many-to-one relationship between the dependents in a family and a family membership.
        Figure 8. Editing the relationships for Dependent – Membership
        Image shows editing the relationships for Dependent – Membership
        Image shows editing the relationships for Dependent – Membership
      2. Select the PrimaryMember-Membership relationship and ensure the first Cascade field is set to all. Enter primaryMember for the Property field. Uncheck the last check box titled "Generate a reference to a collection of MEMBERSHIP in PRIMARYMEMBER".

        Figure 9 shows setting the name of the attribute that provides the aggregate relationship between the primary member and that person's membership with Acme.
        Figure 9. Editing the relationship for PrimaryMember – Membership
        Image shows editing the relationship for PrimaryMember – Membership
        Image shows editing the relationship for PrimaryMember – Membership
      3. Select the PrimaryMember-Address relationship and ensure the first Cascade field is set to all. Enter address for the Property field. Uncheck the last check box titled "Generate a reference to a collection of PRIMARYMEMBER in ADDRESS".

        Figure 10 shows setting the name of the attribute that provides the aggregate relationship between the primary member and that member's residence address.
        Figure 10. Editing the relationship for PrimaryMember – Address
        Image shows editing the relationship for PrimaryMember – Address
        Image shows editing the relationship for PrimaryMember – Address
      4. Select the PrimaryMember-ContactInfo relationship and ensure the first Cascade field is set to all. Enter contactInfo for the Property field. Uncheck the last box titled "Generate a reference to a collection of PRIMARYMEMBER in CONTACTINFO".

        Figure 11 shows setting the name of the attribute that provides the aggregate relationship between the primary member and that member's contact information.
        Figure 11. Editing the relationship for PrimaryMember - ContactInfo
        Image shows editing the relationship for PrimaryMember - ContactInfo
        Image shows editing the relationship for PrimaryMember - ContactInfo
      5. Click Next.
    7. On the Customize Defaults page of the Generate Custom Entities wizard:
    8. Select Identity from the key generator drop-down list. Here, you are indicating the desire to use the identity generation scheme as the approach for generating unique values for primary key attributes for your JPA domain classes.
      • Choose Property for the Entity Access radio button.
      • Select java.util.Set for the Collections Property Type radio button.
      • For the Package field, enter org.acme.membership.domain.
      • Click Next.
    9. On the Customize Individual Entities page of the Generate Custom Entities wizard, you can customize numerous characteristics for both the classes and their underlying attributes. Expand Dependent in the tables and columns list box. Under Dependent, select the BIRTHDATE column. In the corresponding Mapping type drop-down list, select java.util.Calendar.
    10. Repeat Step 4 for the BIRTHDATE column in PRIMARYMEMBER and for the LASTRENEWALDATE and MEMBERSINCE columns in the MEMBERSHIP table.
    11. Click Finish. Feel free to browse the generated JPA entities in the AcmeMembershipApplicationDomain project.

Adjust the JPA entities

Before we can additional business logic, we need to adjust and enhance the JPA entities to ensure that the entities reflect the business and application domain more accurately. You will override the database interpretation of the relationship of some of the entities to be one-to-one rather than many-to-one. This will not affect the referential integrity or primary-foreign key relationships between the tables in the membership database. The reason for doing this is to make the application logic reflect the business rules and constraints that exist between the entities more closely.

Adjust Acme's JPA entities to one-to-one, unidirectional relationships

Assume that to reflect the constraints of the business rules for Acme's membership administration, you make a few adjustments to your JPA entities:

  • Tighten the cardinality (from many-to-one to one-to-one) for some of the relationships.
  • Reduce the navigation flexibility for some of the relationships (from bidirectional to unidirectional).

Both of these changes will make the application more secure and less prone to breaking any of the business rules for Acme's membership application.

Change the cardinality of the relationship.

  1. Switch to the JPA Eclipse perspective.
  2. Open the JPA Primarymember entity.
  3. In the JPA Structure view, select the address attribute.
  4. In the JPA Details view, select the many to one hyperlink, as shown below.
    Figure 12. Changing the cardinality of the relationship
    Image shows changing the cardinality of the relationship
    Image shows changing the cardinality of the relationship
  5. In the Mapping Type Selection dialog window, select One to One and click OK.
  6. In the JPA Details view, uncheck the Optional checkbox and check the All checkbox for the Cascade options.
  7. Repeat Steps 2-5 for these attributes:
    • contactInfo in the Primarymember JPA entity
    • primaryMember in the Membership JPA entity

Important: Step 5 does not change the nature of the relationship of your JPA entities. However, it is a necessary step for making a complex object persistent (for example, an object composed of collections and an aggregation of other complex objects).

Configure a data source and JDBC driver for your WebSphere Liberty server

You will need to configure a JDBC driver and data source for your WebSphere Liberty server to run the Acme Membership Web Application.

  1. In the Servers view of the web perspective, expand the WebSphere Application Server Liberty at localhost instance and double-click the Server Configuration entry, as shown below.
    Figure 13. Opening the Liberty Server Configuration
    Image shows opening the Liberty Server Configuration
    Image shows opening the Liberty Server Configuration
  2. In the Design tab of the Server Configuration editor, select the root Server Configuration entry and click Add.
    Figure 14. Add a data source to the server configuration
    Image shows adding a data source to the server configuration
    Image shows adding a data source to the server configuration
  3. In the Add Element dialog, select Data Source and click OK.
  4. In the Design tab of the Data Source editor, enter jdbc/AcmeMembers for JNDI name and select javax.sql.ConnectionPoolDataSource for type, as shown below. Leave all other default values unchanged and save your editor.
    Figure 15. Configuring a new data source
    Image shows configuring a new data source
    Image shows configuring a new data source
  5. Still in the Data Source editor, click the Add button to add one of the 18 child elements available.
  6. In the Add Element dialog, select Derby Network Client Properties and click OK.
  7. In the Derby Network Client Properties editor,
    1. select create for Create database and enter AcmeMembers for database name.
    2. In the Advanced Properties section, click the Set button next to the password field.
    3. In the Set Password dialog, enter a desired password, select xor from the encoding drop-down list, and click OK.
  8. Save the Server Configuration editor.
  9. Select the Data Source entry you added in the Server Configuration editor and click Add.
  10. In the Add Element dialog, select JDBC Driver and click OK.
  11. In the JDBC Driver editor, click the Add button next to the Shared Library element, as shown below.
    Figure 16. Configuring a new JDBC driver
    Image shows Configuring a new JDBC driver
    Image shows Configuring a new JDBC driver
  12. In the Add Element dialog, select Shared Library and click OK
  13. In the Shared Library editor, click the Add button next to the Fileset, File, Folder elements.
  14. In the Add Element dialog, select Fileset and click OK.
  15. In the Fileset editor, for Base directory, enter the location where the Derby library JAR files reside on your file system, as shown below.
    Figure 17. Specifying the Derby library location
    Image shows specifying the Derby library location
    Image shows specifying the Derby library location
  16. Save the editor.

Run the Acme membership application

You will finally run the Acme membership application on the WebSphere Application Server Liberty environment. You will use a servlet to run the Acme membership function to create a new family membership.

  1. In the Enterprise Explorer view, expand AcmeMembershipApplicationWeb > AcmeMembershipApplicationWeb > Servlets.
  2. Right-click org.acme.membership.admin.AddMembershipServlet and select Run As > Run on Server.

After the WebSphere Liberty server starts, it will invoke your servlet and open a web page, indicating success in creating a new membership. You can inspect the Derby database tables to confirm the addition of the new membership record.

Summary

For this tutorial, we used the Eclipse Oxygen release for Java EE Developers to rapidly generate and customize JPA entities from a Derby database that had tables that use the identity value generation capability to create unique primary keys values and a non-trivial set of relationships between the tables. The Eclipse environment increased your productivity by using views and editors to help you tailor your JPA entities, freeing you from hand-coding the required annotations

you ran your application by using the WebSphere Liberty Server to deploy and run the Acme Membership application.

Acknowledgement

The author thanks Hamid Kalantari for his thoughtful and thorough review of this tutorial.


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