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EJB 3.0 Java Persistence API (JPA) with Oracle TopLink

EJB 3.0 Java Persistence API (JPA) with Oracle TopLink. Bill Lyons Systems Architect Hitachi Consulting wlyons@hitachiconsulting.com. Introduction. Applications using a back end database and a web front end are the most common development architecture in use today.

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EJB 3.0 Java Persistence API (JPA) with Oracle TopLink

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  1. EJB 3.0 Java Persistence API (JPA) with Oracle TopLink Bill Lyons Systems Architect Hitachi Consulting wlyons@hitachiconsulting.com

  2. Introduction • Applications using a back end database and a web front end are the most common development architecture in use today. • Persistence frameworks provide a clean way to separate presentation logic and business logic from database operations. • Persistence frameworks help improve database performance through the use of a mid-tier cache. • The mid-tier improves user experience by caching frequently used data for recall without having to take a trip to the database.

  3. Overview • Examine the development of code that manages interaction between the database and applications. • Take a close look at TopLink - an Oracle owned persistence framework. • Discuss design tradeoffs and common issues associated with using a persistence tier.

  4. EJB 3.0 Top Link Presentation Goals • Develop a high level understanding of J2EE design. • Understand how persistence frameworks simplify development. • Understand persistence tier development choices. • Understand and be able to develop a simple persistence framework using Oracle TopLink.

  5. J2EE Overview

  6. Application Layout

  7. Design artifacts in a typical web based J2EE application We’ll follow the Model-View-Controller OO Design Pattern: TopLink simplifies the development and maintenance of the ‘Model’ portion of an MVC application.

  8. The Persistence Management Problem • Relational Databases and Object Oriented Languages organize data differently. • This makes it difficult for web developers to store and retrieve data from a database. • JDBC code provides access to the database, but is difficult to maintain. • JDBC code can be a significant source of performance problems if not maintained properly. • Persistence frameworks are designed to improve performance while standardizing and simplifying development.

  9. Competing Technologies that solve the persistence problem • Create your own connection pool and write JDBC and SQL code – ugly! • Use a persistence framework: • Hibernate • Spring • JDO • BC4J • TopLink • …and many others…

  10. TopLink: recommended for new development efforts • Has the largest installed base • Easy to use and maintain • Rich feature set • Easy for Java developers to learn: very well documented • Easy for DBAs to understand • Supported by Oracle • However, probably not appropriate for Oracle Apps integration. • Design Limitation/Recommendation: Use Only 1 persistence framework/strategy per database table.

  11. Demo Development Environment Database Oracle XE Integrated Development Environment Oracle JDeveloper 10.1.3.3 Application Server Oracle 10g Application Server (OC4J) (embedded in JDeveloper for today’s demo) Development Platform Windows, Unix, Mac

  12. Typical TopLink Project Artifacts • A JDeveloper Database Connection • TopLink Plain old Java Objects (POJOs) that represent table metadata and table row instances from an Oracle database • An EJB session bean that allows users to connect to the persistence tier and perform data operations. • Developer constructed queries. • Code to test out the persistence implementation using an EJB test client.

  13. TopLink Getting Started • Download and install database (or connect to one) • Download and install JDeveloper 10.1.3.3 • Build tables, indexes, sequences and constraints on the database: (We’ll use the Oracle SRDemo today as an example) • SRDemo Tables, Indexes and Sequences are generated by running the build.sql script bundled with SRDemo • Be sure to get the SRDemo for TopLink – not ADF/BC or SRDemo for 4GL. There are different versions out there

  14. TopLink Getting Started (cont.) • Create a Connection from JDeveloper to the Database. • Create a new TopLink project and workspace in JDeveloper. • Run the TopLink wizard to create EJB 3.0 JPA Entity Objects and an EJB Session Bean. • Refine the design if necessary. • Deploy to an application server. • Write a test client to test out the implementation. • If everything works, version the source code along with the database DDL.

  15. SRDemo Schema

  16. TopLink My First Persistence Tier • Start Database • Start JDeveloper • Create a Connection to the Database in JDeveloper • Create an Application and Workspace in JDeveloper

  17. Create a new Application and Workspace in JDeveloper You can type anything for Application Name and Directory Name. In general, JDeveloper like most Java Development Environments will behave inconsistently with spaces between characters so don’t use them in names or directory paths. Choose Web Application [JSF, EJB, TopLink] for the Application Template and click OK.

  18. Create EJB 3.0 Entity Objects using TopLink • A TopLink Entity Object will be created for each table and view referenced • Entity Objects define database tables and operations that can be performed on entity rows. • Database views and synonyms are also viable selections for TopLink entities. • TopLink can reference database sequences or stored procedures to populate columns

  19. Using JDeveloper wizards to create TopLink objects using EJB 3.0 APIs Be sure to choose EJB and Entities from Tables (JPA/EJB 3.0) when creating the persistence tier

  20. Examining the Generated TopLink Entity Objects A Java Entity object will be created for every table that is selected in the wizard. It is possible to also select database views and synonyms for generation. The Entity object contains table metadata, get/set methods for each column and named queries for the Entity. A separate Java object will be created for querying and enforcing primary key constraints.

  21. Examining the Generated Java Source Code: Table Code @Entity @NamedQuery( name = "ExpertiseAreas.findAll", query = "select o from ExpertiseAreas o" ) @Table( name = "EXPERTISE_AREAS" ) @IdClass( ExpertiseAreasPK.class ) public class ExpertiseAreas implements Serializable { @Column( name="EXPERTISE_LEVEL", nullable = false ) private String expertiseLevel; private String notes; @Id @Column( name="PROD_ID", nullable = false, insertable = false, updatable = false ) private Long prodId; @Id @Column( name="USER_ID", nullable = false, insertable = false, updatable = false ) private Long userId; @ManyToOne @JoinColumn( name = "PROD_ID", referencedColumnName = "PROD_ID" ) private Products products;

  22. Examining the Generated Java Source Code: Column Code //… public String getExpertiseLevel() { return expertiseLevel; } public void setExpertiseLevel( String expertiseLevel ) { this.expertiseLevel = expertiseLevel; } public String getNotes() { return notes; } public void setNotes( String notes ) { this.notes = notes; } public Long getProdId() { return prodId; } public void setProdId( Long prodId ) { this.prodId = prodId; } //… and so on…

  23. Create a class diagram from the Entity Objects From inside of the rmoug Model project right click and choose New… The New Gallery appears. Choose Diagrams… Database Diagram Name the diagram SRDemo class diagram. Then drag and drop the Java Beans that we created in the previous step. Arrange the diagram objects so that all elements are visible.

  24. JDeveloper class diagram

  25. Build a session bean to expose the Entities and provide session functionality From the New Gallery choose Business Tier, EJB, Session Bean (EJB 1.1/2.x/3.0)… Accept all defaults.

  26. Purpose of the Session Bean • Encapsulates all of the behavior needed by a java service (could be web, swing client, or web service) so that a client can connect and query objects out of the persistence tier. • Deployed with our POJOs to an EJB container. • We’ll use OC4J: a local application server embedded in JDeveloper that is fully EJB 3.0 compliant

  27. Examining the Session Bean Generated Source Code @Stateless( name="SessionEJB" ) public class SessionEJBBean implements SessionEJB, SessionEJBLocal { @PersistenceContext( unitName="Model" ) private EntityManager em; public Object mergeEntity( Object entity ) { return em.merge(entity); } public Object persistEntity( Object entity ) { em.persist(entity); return entity; } /** <code>select o from ExpertiseAreas o</code> */ public List<ExpertiseAreas> queryExpertiseAreasFindAll() { return em.createNamedQuery("ExpertiseAreas.findAll").getResultList(); } public void removeExpertiseAreas( ExpertiseAreas expertiseAreas ) { expertiseAreas = em.find(ExpertiseAreas.class, new ExpertiseAreasPK(expertiseAreas.getProdId(), expertiseAreas.getUserId())); em.remove(expertiseAreas); }

  28. Build a simple test client To create a test client right click on the SessionEJBBean.java that we generated earlier in the project and choose New Sample Java Client…

  29. Examine the Generated Code for the Test EJB Client public class SessionEJBClient { public static void main( String [] args ) { try { final Context context = getInitialContext(); SessionEJB sessionEJB = (SessionEJB)context.lookup("SessionEJB"); System.out.println( sessionEJB.queryExpertiseAreasFindAll( ) ); // Call other methods of the Remote object to access the EJB // sessionEJB.mergeEntity( expertiseAreas ); // sessionEJB.persistEntity( expertiseAreas ); // sessionEJB.removeExpertiseAreas( expertiseAreas ); } catch ( Exception ex ) { ex.printStackTrace(); } }

  30. Testing it all out • Run the SessionEJBBean • This deploys the SessionEJBBean, connection and Entity objects to the OC4J container embedded in JDeveloper. • Run the SessionEJBClient • The client will connect to the Web Application Server, locate the SessionEJBBean and execute methods on the remote session bean. • Remember, you must run the SessionEJBBean first to deploy it to the container, otherwise you will get an error! • As you make changes to your Entities, remember you will have to redeploy (make/rebuild, run) in order to have the changes take effect on the App Server.

  31. It works! …sort of ;-( • What does this mean? com.rmoug.model.ExpertiseAreas@193c0cf

  32. Refining the generated code • Need a way to query (and see) data • Need a way to make changes to data • Need a way to commit work

  33. TopLink CRUD query methods Match Up Question: SQL TopLink SELECT removeEntity() INSERT queryEntityNameFindAll() UPDATE persistEntity() DELETE mergeEntity() ?

  34. TopLink CRUD query operations Match Up Answer SQL TopLink SELECT removeEntity() INSERT queryEntityNameFindAll() UPDATE persistEntity() DELETE mergeEntity()

  35. TopLink CRUD query operations: ANSWER SQL TopLink SELECT queryEntityNameFindAll() INSERT persistEntity() UPDATE mergeEntity() DELETE removeEntityName()

  36. Select All data query Selecting data using the queryEntityNameFindAll() method: // Selects and prints out all rows: System.out.println("Products Query Result:"); List<Products> productsList = sessionEJB.queryProductsFindAll(); for ( Products p: productsList ) { System.out.println( "Product ID: " + p.getProdId() ); System.out.println( "Product Name: " + p.getName() ); System.out.println( "Product Description: " + p.getDescription() ); }// end for We’ll Build a named query with a where clause later in the session…

  37. Inserting Data using the persistEntity() method // Inserts a row into the products table: Products p1 = new Products(); p1.setName( “IOUG Washing Machine" ); p1.setDescription( "Having fun at IOUG" ); sessionEJB.persistEntity( p1 );

  38. Updating data using the mergeEntity() method: // Perform an update: // productsList.size() returns the size of the List // Remember: Java like C/C++ is zero based so we must // subtract 1 to find the last element in the List: Products p2 = new Products(); p2 = productsList.get( productsList.size() - 1 ); p2.setName( “IOUG iPod" ); p2.setDescription( "We updated this row!" ); sessionEJB.mergeEntity( p2 );

  39. Delete data using the removeEntityName() method // delete a Product from the List Products p3 = new Products(); p3 = productsList.get( productsList.size() - 1 ); sessionEJB.removeProducts( p3 );

  40. How do you find an Entity Row by Primary Key? • Need to create a new Named Query • Expose the new Query in the Session Bean • Test it out in the Client Test Harness

  41. Find a row by primary Key: Step 1. Create a Named Query in Products.java EntityBean Creating a new Named Query. If you have more than 1 query in a POJO, you’ll need to wrap the named queries in an @NamedQueries Annotation. @NamedQueries({ @NamedQuery( name = "Products.findAll", query = "select o from Products o" ) , @NamedQuery( name = "Products.findByProdId", query = "select p from Products p where p.prodId = :prodId") }) Code that we added

  42. Find a row by primary Key: Step 2. Expose the new method • Expose the findByProdId() method in the Session Bean: Right click on the SessionEJBBean.java file and then Select Edit Session Façade…

  43. Find a row by primary Key: Step 3. • Expose/Enable methods in the Session Façade wizard: Check the newly created Products.findByProdId method. This will make it available to clients at runtime.

  44. Method generated for our new query in the session bean: /** <code>select p from Products p where p.prodId = :prodId</code> */ public List<Products> queryProductsFindByProdId( Object prodId ) { return em.createNamedQuery( "Products.findByProdId“ ) .setParameter( "prodId", prodId ).getResultList(); } This cryptic little stub performs the following. • Accepts a prodId parameter. • Creates an instance of the findByProdId NamedQuery using the Entity Manager instance em. • Sets the required prodId parameter to the value passed to this method. • Returns a java.util.List object that contains all of the objects (rows) that satisfied this query by invoking the getResultList() method of the NamedQuery.

  45. Test our new query in the EJB test client System.out.println( "Products by Prod ID Query Result:" ); List<Products> productsList = sessionEJB.queryProductsFindByProdId( 100 ); for ( Products p: productsList ) { System.out.println( "Prod ID: " + p.getProdId() ); System.out.println( "Name: " + p.getName() ); System.out.println( "Description: " + p.getDescription() ); }

  46. Database Transactions • What if I need a database transaction? • When we accepted the default settings, it set up the Entity objects to use Container Managed Persistence (CMP) and optimistic locking for row data. • This means that persistence operations will commit and rollback work automatically. • To get finer grained control you’ll need to review TopLink’s transaction documentation in the Developer’s Guide. • TopLink provides support for commit, rollback and two-phase commit as expected.

  47. Handling Schema Design Changes • Have a look at Offline Database Object Generation/Reconciliation.

  48. Persistence Framework Issues • Very important to understand the relationship between your persistence framework and the database regarding synchronization. • Very important to implement and understand a synchronization strategy so that database/mid-tier consistency is maintained.

  49. Recommendations • Use a persistence framework • Have a data architect role on project that works closely with the database administrator responsible for the schema administration. • Watch out for DML that is performed outside of the persistence framework • Get to know how to tune your persistence framework • Be on the lookout for rogue developers

  50. Helpful information • EJB 3.0 TopLink Presentation Materials and Source Code • http://www.4shared.com/dir/5686418/9daee38b/RMOUG_2008.html • Oracle TopLink Homepage • www.oracle.com/technology/products/ias/toplink/index.html • EJB 3.0 Resources • www.oracle.com/technology/tech/java/ejb30.html • Oracle JDeveloper Homepage • www.oracle.com/technology/products/jdev/index.html • EJB 3.0 Specification • java.sun.com/products/ejb/docs.html • TopLink Cache Invalidation • www.oracle.com/technology/products/ias/toplink/technical/tips/DbChangeNotification/index.htm • Spy Mid-Tier SQL to Database • www.p6spy.com/

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