Chapter 9b: Persistence Tier: Entity Beans

1
Chapter 9bPersistence TierEntity Beans
Reference Eclipse WTP
2
Objectives

• Entity Beans
• BMP and CMP
• Preparing JBoss and XDoclet
• Working with CMPs in Eclipse WTP
• EJB Query Language

3
Persistence Layer Designs
Client and Presentation Tier
Business Tier
Service Layer (Facades)
Domain Model (POJO)
Data Layer (Data Access Object Interfaces)
Persistence Tier
1. JDBC (JDBC API)
2. EJB, CMP (Remote Stubs)
3. O/R Mapping (ORM Framework)
4
Entity EJBs

• Entity beans represent persistent data
• Use entity beans as the interface between Java
  components and relational or object-oriented
  databases
• The container uses the primary key to locate the
  data when a client requests an entity bean and
  creates only one bean to represent that data in a
  Java object

5
EJB to Database Schema Mapping

• Three approaches to database schema mapping
• Bottom-up mapping
• occurs when you have a database and can design
  your EJBs to match the tables and columns defined
  in the database schema
• See textbook tutorial
• Top-down mapping
• possible when a new database is required and Java
  developers are allowed to create databases
• Meet-in-the-middle mapping
• Map to existing database and add new
  attributes/columns

6
Entity Beans BMP and CMP

• The EJB specification allows two approaches
• Container Managed Persistence (CMP)
• involves declaring the mapping between the
  deployment descriptor and delegating all code
  generation to the container
• See textbook tutorial
• Bean Managed Persistence (BMP)
• Do-it-yourself (DIY) solution
• DIY alternative EJB Session Beans JDBC
• Note not covered in this course

7
Preparing JBoss and XDoclet

• Reference Pages 393 397
• XDoclet set version to 1.2.3
• ejbdoclet set JBoss version to 4.0

8
Working with CMPs

• Reference Pages 396 - 401
• General Steps using Eclipse WTP
• 1. Add a CMP EJB
• Map table to CMP Entity Bean
• 2. Modify CMP Entity Bean (e.g., LeagueBean)
• XDoclet generates
• Home and remote interfaces
• Data Source reference
• 3. Write the EJB Client (e.g., servlet)
• 4. Test the EJB Client

9
1. Add a LeagueBean CMP

• Right-click LeaguePlanetEJB project
• Invoke New XDoclet Enterprise JavaBean
• Java Package com.leagueplanet.cmp
• Class Name LeagueBean
• Select id as primary key.

10
Sample CMP Entity Bean (1)

• package com.leagueplanet.cmp
• public abstract class LeagueBean implements
  javax.ejb.EntityBean
• public LeagueBean()
• public java.lang.Integer ejbCreate(int id,
  String name) throws javax.ejb.CreateException
• setId(id)
• setName(name)
• // EJB 2.0 spec says return null for CMP
  ejbCreate methods.
• return null
• public void ejbPostCreate() throws
  javax.ejb.CreateException
• public abstract java.lang.Integer getId()
• public abstract void setId(java.lang.Integer
  id)
• public abstract java.lang.String getName()
• public abstract void setName(java.lang.String
  name)

11
Sample CMP Entity Bean (2)

• public void ejbActivate() throws EJBException,
  RemoteException
• public void ejbLoad() throws EJBException,
  RemoteException
• public void ejbPassivate() throws EJBException,
  RemoteException
• public void ejbRemove() throws RemoveException,
  EJBException,
• RemoteException
• public void ejbStore() throws EJBException,
  RemoteException
• public void setEntityContext(EntityContext arg0)
  throws EJBException,
• RemoteException
• public void unsetEntityContext() throws
  EJBException, RemoteException

12
2. Modify CMP Entity Bean

• Reference Textbook page 403
• Using XDoclet in Eclipse WTP, update
  _at_jboss.persistence XDoclet tag with
• _at_jboss.persistence datasource"java/Leagu
  eDS" datasource-mapping"Derby"
  table-name"APP.GAME" create-table"true"
  remove-table"false" alter-table"true"

13
JBoss and Data Sources

• Entity beans locate data sources (e.g., Derby
  JDBC driver) by looking up the name (e.g.,
  LeagueDS) in a JNDI server (i.e., part of JBoss)
• JBoss loads the data source configuration (e.g.,
  derby-ds.xml) at start-up
• You must restart JBoss when configuration file is
  modified.

14
Define Data Source

• Define data source in the JBoss-specific
  configuration file (e.g., derby-ds.xml)
• Location C\dev\appservers\jboss-4.2.2.GA\server\
  default\deploy
• ltlocal-tx-datasourcegt
• ltjndi-namegtLeagueDSlt/jndi-namegt
• ltconnection-urlgt jdbcderby//localhost1527
  /leagueDBlt/connection-urlgt
• ltdriver-classgtorg.apache.derby.jdbc.ClientDr
  iverlt/driver-classgt
• ltuser-namegttestlt/user-namegt
• ltpasswordgttestlt/passwordgt
• ltmin-pool-sizegt5lt/min-pool-sizegt
• ltmax-pool-sizegt20lt/max-pool-sizegt
• ltidle-timeout-minutesgt5lt/idle-timeout-minute
  sgt
• lt/local-tx-datasourcegt

15
Add a Service Layer for CMP (1)

• E.g., IceHockeyCMPDAOImpl class
• Add createLeagueFromCMP() method as follows
• private League createLeagueFromCMP(
  com.leagueplanet.cmp.League cmp)throws
  SQLException, ParseException, RemoteException
      League league new League()   
  league.setId(cmp.getId().intValue())   
  league.setName(cmp.getName())    return
  league

16
Add a Service Layer for CMP (2)

• Update findLeague(long id) method as follows
• public League findLeague(long id)     // League
  leaguenew League(id, "Rosehill Girl's Hockey
  League")    int leagueId (int) id    League
  league null    try        
  com.leagueplanet.cmp.League cmp
  com.leagueplanet.cmp.LeagueUtil           
  .getHome().findByPrimaryKey(new
  Integer(leagueId))        league
  createLeagueFromCMP(cmp)       
  league.getSchedules().add(findSchedule(leagueId))
      catch (Exception e)        
  e.printStackTrace()        return league

17
3. Write EJB Client

• E.g., LeagueCRUDServlet class
• protected void doGet(HttpServletRequest request,
  HttpServletResponse response) throws
  ServletException, IOException
• try
• // Test cases for LeagueCMP
• System.out.println("1. Create a new league
  (direct approach using remote home)")
• int id Integer.parseInt(request.getParameter("i
  d"))
• String name request.getParameter("name")
• // this will create a new row in Derby DB
• LeagueUtil.getHome().create(id, name)
• System.out.println("2. Find league (direct
  approach using remote home)")
• com.leagueplanet.cmp.League dbrow
  LeagueUtil.getHome().findByPrimaryKey(id)
• System.out.println("League id "
  dbrow.getId() " name" dbrow.getName())

18
Sample EJB Client (2)

• System.out.println("3. Update name of league
  (direct approach using local home)")
• // creates an instance of league facade, then
  calls the find method
• LeagueLocal localdbrow LeagueUtil.getLocalHome()
  
• .findByPrimaryKey(id)
• // this will update name column in Derby DB
• localdbrow.setName(name " - correction")
• System.out.println("4. Find league (direct
  approach using local home)")
• localdbrow LeagueUtil.getLocalHome().findByPrima
  ryKey(id)
• System.out.println("League id "
  localdbrow.getId() " name"
  localdbrow.getName())

19
Sample EJB Client (3)

• System.out.println("5. Delete current league
  record")
• // this will delete the row in Derby DB
• localdbrow.remove()
• System.out.println("6. Find deleted league
  (multi-tier approach using facade remote
  home)")
• // creates an instance of league facade, then
  calls the find method
• LeagueFacade facade LeagueFacadeUtil.getHome().
  create()
• // The findLeague() method in facade calls
  findByPrimaryKey() using local home
• // and returns a POJO (non-CMP) League object
• League league facade.findLeague(id)
• System.out.println("League id "
  league.getId() " name" league.getName())
• catch (Exception e)
• System.err.println("exception occurred. "
  e.getMessage())

20
4. Test EJB Client

• http//localhost8080/LeaguePlanetWeb/LeagueCRUDSe
  rvlet?id6nameLeague6
• Console Output
• 174452,593 INFO STDOUT 1. Create a new league
  (direct approach using remote home)
• 174452,609 INFO STDOUT 2. Find league (direct
  approach using remote home)
• 174452,609 INFO STDOUT League id 6
  nameLeague6
• 174452,609 INFO STDOUT 3. Update name of
  league (direct approach using local home)
• 174452,625 INFO STDOUT 4. Find league (direct
  approach using local home)
• 174452,625 INFO STDOUT League id 6
  nameLeague6 - correction
• 174452,625 INFO STDOUT 5. Delete current
  league record
• 174452,640 INFO STDOUT 6. Find deleted league
  (multi-tier approach using facade remote home)
• 174452,640 ERROR STDERR javax.ejb.ObjectNotFou
  ndException No such entity!

21
EJB Query Language

• Enterprise JavaBean Query Language (EJB QL) was
  introduced in the EJB 2.0 specification to
  support the abstract persistence model
• EJB QL language for expressing the equivalent of
  SQL SELECT statements for CMP beans
• Useful for generating code for custom Find method
• E.g. findAll() method
• _at_ejb.finder query"SELECT OBJECT(a) FROM
  LeagueSCHEMA as a"
• signature"java.util.Collection findAll()

22
Comparing EJB QL and SQL Statements
Note More details in Mastering EJB 3.0, Chapter 9
23
Sample Finder Methods XDoclet Tags in
GameBean.java

• _at_ejb.finder
• query"SELECT OBJECT(a) FROM GameSCHEMA as a"
  
• signature"java.util.Collection findAll()"
• _at_ejb.finder
• query"SELECT OBJECT(a) FROM GameSCHEMA as a
  WHERE a.scheduleid ?1"
• signature"java.util.Collection
  findScheduleGames(int scheduleid)"

24
Generated Deployment Descriptor (ejb-jar.xml)
ltquerygt ltquery-methodgt
ltmethod-namegtfindAlllt/method-namegt
ltmethod-paramsgt lt/method-paramsgt
lt/query-methodgt
ltejb-qlgtlt!CDATASELECT OBJECT(a) FROM GameSCHEMA
as a gtlt/ejb-qlgt lt/querygt
ltquerygt ltquery-methodgt
ltmethod-namegtfindScheduleGameslt/method-namegt
ltmethod-paramsgt
ltmethod-paramgtintlt/method-paramgt
lt/method-paramsgt lt/query-methodgt
ltejb-qlgtlt!CDATASELECT OBJECT(a) FROM
GameSCHEMA as a WHERE a.scheduleid
?1gtlt/ejb-qlgt lt/querygt
25
Next Steps

• Tutorials
• Chapter 9 Iteration 3
• Lab
• EJB CMP (add, find, edit and delete League)
• Assignment 4