Persistence Models Margaret Smith

Overview Java Data Objects (JDO) Enterprise Java Beans (EJB) 3.0 Demos and code

What is JDO? The Java Data Objects (JDO) API is a standard interface-based Java model abstraction of persistence developed as Java Specification Request 12 (JSR 12) under the Java Community Process.

What is EJB 3.0? Enterprise Java Beans (EJB) 3.0 is a deep overhaul and simplification of the EJB specification. EJB 3.0's goals are to simplify development and focus more on writing plain old java objects (POJOs) rather than on complex EJB APIs. JSR-220 of the Java Community Process.

How are EJB and JDO related? Java EE or SE EJB 3.0 Hibernate TopLink JDO Other technologies… Plain old Java objects (POJOs) and dependency injection

Earlier EJB Versions vs EJB 3.0 Focus on plain Java classes Strong emphasis on Java metadata annotations eliminates need for deployment descriptor Annotations take the form and are used to express meta-data Specification of programmatic defaults Provides default database Less transactional code

Step 1: Design your domain/model classes as you would do normally Step 2: Define their persistence definition using Meta-Data Step 3: Compile your classes, and instrument them (using a JDO enhancer) Step 4: Generate the database tables where your classes are to be persisted Step 5: Write your code to persist your objects within the DAO layer Step 6: Run your application Step 1: Design your domain/model classes as you would do normally Step 2: Define their persistence definition using annotations as Meta-Data Step 3: Compile your classes Step 4: Run your application Optional step: specify a database other than the default Hsqldb database The JDO Process Creating an application The EJB 3.0 Process

Usage Models User interface input HSQLDB User interface input MySQL JDO ModelEJB 3.0 Model Server Database Driver Enhanced POJOs Annotated POJOs

Demos and code Store application where objects are Product and Book Plain java objects PersistenceManager object More error checking Investment calculator application where objects are Fund and EntityCalculator Plain annotated java objects EntityManager object JDOEJB 3.0

JDO: Schema file <!DOCTYPE jdo PUBLIC "-//Sun Microsystems, Inc.//DTD Java Data Objects Metadata 2.0//EN" " <class name="Book" identity-type="datastore" persistence-capable-superclass="org.jpox.tutorial.Product">

JDO: Persistence Manager private static PersistenceManager createPersistenceManager() throws IOException { Properties properties = new Properties(); InputStream is=Main.class.getClassLoader().getResourceAsStream("jpox.properties"); if (is == null) { throw new FileNotFoundException("Could not find jpox.properties file that defines the JPOX persistence setup."); } properties.load(is); PersistenceManagerFactory pmfactory = JDOHelper.getPersistenceManagerFactory(properties); PersistenceManager pm = pmfactory.getPersistenceManager(); return pm; }

JDO: Database interaction …. PersistenceManager pm = createPersistenceManager(); // Persistence of a Product and a Book. Transaction tx=pm.currentTransaction(); try{ tx.begin(); Product product = new Product("Sony Discman","A standard discman from Sony",49.99); Book book = new Book("Lord of the Rings by Tolkien","The classic story",49.99,"JRR Tolkien", " ", "MyBooks Factory"); pm.makePersistent(product); pm.makePersistent(book); tx.commit(); System.out.println("Product and Book have been persisted"); } finally{ if (tx.isActive()) { tx.rollback(); } pm.close(); } ….

EJB: Fund.java import javax.persistence.*; = "fund") public class Fund implements Serializable { private int id; private String name; private double growthrate; public Fund () { } public Fund (String name, double growthrate) { this.name = name; this.growthrate = public int getId () { return id; } public void setId (int id) { this.id = id; } EJB 3.0 requires a default constructor Denotes a primary key automatically generated by the server

EJB: EntityCalculator.java import trail.entity.beans.*; import javax.ejb.*; import javax.persistence.*; import java.sql.Timestamp; import public class EntityCalculator implements Calculator // (unitName="cal") protected EntityManager em; public void addInvestor (String name, int start, int end) { Investor investor = new Investor (name, start, end); em.persist (investor); } public void addFund (String name, double growthrate) { Fund fund = new Fund (name, growthrate); em.persist (fund); } …..Continued next slide Identifies class as a stateless session bean Injects an EntityManager object Saves entity bean instance to database as a new row

EJB: EntityCalculator.java public double calculate (int fundId, int investorId, double saving) { Investor investor = em.find(Investor.class, Integer.valueOf(investorId)); Fund fund = em.find(Fund.class, Integer.valueOf(fundId)); int start = investor.getStartAge(); int end = investor.getEndAge(); double growthrate = fund.getGrowthrate(); double tmp = Math.pow(1. + growthrate / 12., 12. * (end - start) + 1); double result = saving * 12. * (tmp - 1) / growthrate; Timestamp ts = new Timestamp (System.currentTimeMillis()); TimedRecord rec = new TimedRecord (fund, investor, saving, result, ts); em.persist (rec); return result; } …Continued next slide Find and retrive entity bean by using entity name and entity id

EJB: EntityCalculator.java public Collection getFunds () { return em.createQuery("from Fund f").getResultList(); } public Collection getInvestors () { return em.createQuery("from Investor p").getResultList(); } public Collection getRecords () { return em.createQuery("from TimedRecord r order by r.ts desc").getResultList(); } EJB QL statement; returns a collection of entity beans matched by query

EJB: Client code private EntityCalculator cal = null; public void jspInit () { try { InitialContext ctx = new InitialContext(); cal = (EntityCalculator) ctx.lookup ("EJB3Trail/EntityCalculator/local"); } catch (Exception e) { e.printStackTrace (); } public void service (Request req, Response rep) { // double res = cal.calculate(fund, investID, saving); } If the application is deployed in a EAR file, the default JNDI name is the EAR-FILE- BASE-NAME/EJB- CLASS-NAME/local for the stub for local interface; same for local and remote interfaces

Conclusion JDO EJB 3.0 Questions

System Requirements JDO Demo JPOX: Java Persistent Objects MySQL database MySQL Connector/J database driver EJB 3.0 Demo EJB 3.0 Trailblazer from JBoss JBoss EJB 3.0 module from JBoss (may be downloaded together with JBoss 4.0.4)

References EJB/JDO Persistence FAQ. Sun Developer Network (SDN). Version 2h 23-Feb JBoss Trailblazers and Demo Applications. JBoss: The Professional Open Source Company.. EJB 3 Trailblazer. JPOX rc-1 Out Now. JPOX: Java Persistent Objects. JPOX – Tutorial. JPOX: Java Persistent Objects. MySQL Connector/j. MySQL.