EJB 3.0 Puzzlers. Mike Keith, Oracle Corp. Colorado Software Summit: October 21 26, 2007

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1 EJB 3.0 Puzzlers Mike Keith, Oracle Corp. Slide 1

2 About Me Co-spec Lead of EJB 3.0 (JSR 220) and Java EE 5 (JSR 244) expert group member Currently working on Java EE 6 (JSR 316), EJB 3.1 (JSR 318), and JPA 2.0 (JSR 317) groups Co-author Pro EJB 3: Java Persistence API Persistence/EJB/Container Architect for Oracle 15+ years experience in distributed, server-side and persistence implementations Presenter at numerous conferences and events Slide 2

3 Goal To examine some of the subtleties of EJB 3.0 and JPA (and have fun doing it) Slide 3

4 Rules of the Game 1. Package and import (including static import) statements may be assumed. To conserve space they are not listed. 2. Client code is not completely specified. It is the invocation on session beans or the persistence layer. 3. Some of the simpler classes/interfaces are not specified. They can be assumed to be present and to be defined as expected (as is a persistence.xml file). 4. The print() method is a shorthand for System.out.print(). Slide 4

5 Puzzle #1 Madness to the AnInterface ejb; return ejb.method1(); Answers a) 42 d) EntityNotFoundException b) AnEntity(5) e) Some other exception c) Null f) Depends on implementation Slide 5

6 Puzzle #1 Madness to the public class ABean implements AnInterface EntityManager em; public Object method1() { method2(); return em.find(anentity.class, 5); private void method2() { AnEntity e = new AnEntity(); e.setid(5); em.persist(e); Slide 6

7 Puzzle #1 Madness to the public class AnEntity private int id; public int getid() { return this.id; public void setid(int id) { this.id = id; Slide 7

8 Puzzle #1 Madness to the AnInterface ejb; return ejb.method1(); Answers a) 42 d) EntityNotFoundException b) AnEntity(5) e) Some other exception c) Null f) Depends on implementation Slide 8

9 Puzzle #1 Madness to the public class ABean implements AnInterface EntityManager em; (unitname="myunit") public Object method1() { method2(); return em.find(anentity.class, 5); private void method2() { AnEntity e = new AnEntity(); e.setid(5); em.persist(e); Spec allows a but doesn't specify what it is Slide 9

10 Puzzle #1 Madness to the AnInterface ejb; return ejb.method1(); Answers a) 42 d) EntityNotFoundException b) AnEntity(5) e) Some other exception c) Null f) Depends on implementation Slide 10

11 Puzzle #2 Identity AnInterface ejb; ejb.persist(5); return ejb.method1(5); Answers a) true d) Some other exception b) false e) Depends on implementation c) NullPointerException f) None of the above Slide 11

12 Puzzle #2 EM, unitname= punit ) public class ABean implements AnInterface SessionContext punit ) EntityManager cm_em; public void persist(int id) { cm_em.persist(new AnEntity(id)); public boolean method1(int id) { EntityManager em =(EntityManager)ctx.lookup( EM ); AnEntity e1 = em.find(anentity.class, id) return (e1 == cm_em.find(anentity.class, id)); Slide 12

13 Puzzle #2 Identity public class AnEntity private int id; public AnEntity(int id) { this.setid(id); public int getid() { return this.id; public void setid(int id) { this.id = id; Slide 13

14 Puzzle #2 Identity AnInterface ejb; ejb.persist(); return ejb.method1(); Answers a) true d) Some other exception b) false e) Depends on implementation c) NullPointerException f) None of the above Slide 14

$EntityManager cm_em; public void persist(int id) { cm_em.$

15 Puzzle #2 EM, unitname= punit ) public class ABean implements AnInterface SessionContext punit ) EntityManager cm_em; public void persist(int id) { cm_em.persist(new AnEntity(id)); Injected EM and looked up EM point to the same PC public boolean method1(int id) { EntityManager em =(EntityManager)ctx.lookup( EM ); AnEntity e1 = em.find(anentity.class, id) return (e1 == cm_em.find(anentity.class, id)); Slide 15

Puzzle #2 Identity Crisis @Entity public class AnEntity { @Id private int id; No-arg constructor required, but not generated when a single-arg one is

16 Puzzle #2 Identity public class AnEntity private int id; No-arg constructor required, but not generated when a single-arg one is declared public AnEntity() { public AnEntity(int id) { this.setid(id); public int getid() { return this.id; public void setid(int id) { this.id = id; Slide 16

17 Puzzle #2 Identity AnInterface ejb; ejb.persist(); return ejb.method1(); Answers a) true d) Some other exception b) false e) Depends on implementation c) NullPointerException f) None of the above Slide 17

18 Puzzle #3 Identity Crisis (Part AnInterface ejb; ejb.persist(); return (ejb.method1() && ejb.method2()); Answers a) true d) Some other exception b) false e) Depends on implementation c) NullPointerException f) None of the above Slide 18

19 Puzzle #3 Identity Crisis (Part public class ABean implements AnInterface punit,type=extended) EntityManager AnotherInterface slbean; AnEntity entity1 = new AnEntity(5); AnEntity entity2 = new AnEntity(10); public void persist() { public boolean method1() { return (entity1 == public boolean method2() { em.persist(entity2); return (entity2 == slbean.method2(10)); Slide 19

20 Puzzle #3 Identity Crisis (Part public class SLBean implements AnotherInterface punit ) EntityManager em; public Object method1(int id) { return em.find(anentity.class, id); public Object method2(int id) { return em.merge(new AnEntity(id)); Slide 20

21 Puzzle #3 Identity Crisis (Part AnInterface ejb; ejb.persist(); return (ejb.method1() && ejb.method2()); Answers a) true d) Some other exception b) false e) Depends on implementation c) NullPointerException f) None of the above Slide 21

Puzzle #3 Identity Crisis (Part 2) @Stateful public class ABean implements AnInterface { @PersistenceContext(unitName= punit,type=extended) EntityManager em; @EJB AnotherInterface slbean; AnEntity

22 Puzzle #3 Identity Crisis (Part public class ABean implements AnInterface punit,type=extended) EntityManager AnotherInterface slbean; AnEntity entity1 = new AnEntity(5); AnEntity entity2 = new AnEntity(10); Extended PC is propagated across transaction into each SLSB method public void persist() { public boolean method1() { return (entity1 == public boolean method2() { em.persist(entity2); return (entity2 == slbean.method2(10)); Slide 22

Puzzle #3 Identity Crisis (Part 2) @Stateless public class SLBean implements AnotherInterface { @PersistenceContext(unitName= punit ) EntityManager em; public Object method1(int id) { return em.

23 Puzzle #3 Identity Crisis (Part public class SLBean implements AnotherInterface punit ) EntityManager em; public Object method1(int id) { return em.find(anentity.class, id); public Object method2(int id) { return em.merge(new AnEntity(id)); Merge returns a managed entity with the same id, which is the same entity persisted in the calling method Slide 23

24 Puzzle #3 Identity Crisis (Part AnInterface ejb; ejb.persist(); return (ejb.method1() && ejb.method2()); Answers a) true d) Some other exception b) false e) Depends on implementation c) NullPointerException f) None of the above Slide 24

25 Puzzle #4 A Merge Without a RemoteInterface ejb; return ejb.method(5); Answers a) null d) Some other exception b) AnEntity(5) e) Depends on implementation c) ClassCastException f) None of the above Slide 25

26 Puzzle #4 A Merge Without public class ABean implements AnInterface punit ) EntityManager em; public Object method(int id) { return em.merge(new AnEntity(id)); Slide 26

27 Puzzle #4 A Merge Without a public class AnEntity int id; String data; public AnEntity() { public AnEntity(int id) { this.setid(id); public int getid() { return this.id; public void setid(int i) { this.id = i; public String getdata() { return this.data; public void setdata(string d) { this.data = d; Slide 27

28 Puzzle #4 A Merge Without a RemoteInterface ejb; return ejb.method(5); Answers a) null d) Some other exception b) AnEntity(5) e) Depends on implementation c) ClassCastException f) None of the above Slide 28

29 Puzzle #4 A Merge Without public class ABean implements AnInterface punit ) EntityManager em; public Object method(int id) { return em.merge(new AnEntity(id)); Slide 29

30 Puzzle #4 A Merge Without a public class AnEntity { implements Serializable int id; String data; Entity is being returned from a remote method so it must be Serializable public AnEntity() { public AnEntity(int id) { this.setid(id); public int getid() { return this.id; public void setid(int i) { this.id = i; public String getdata() { return this.data; public void setdata(string d) { this.data = d; Slide 30

31 Puzzle #4 A Merge Without a RemoteInterface ejb; return ejb.method(5); Answers a) null d) Some other exception b) AnEntity(5) e) Depends on implementation c) ClassCastException f) None of the above Slide 31

32 Puzzle #5 Callback AnInterface ejb; ejb.method1(); Answers a) PreP p p PostP PreU u u PostU b) PreP p PostP PreU PostU p u u c) PreP PostP PreU PostU p p u u d) An exception e) Depends on implementation f) None of the above Slide 32

33 Puzzle #5 Callback public class AnEntity int id; String data; public AnEntity() { public AnEntity(int id) { this.setid(id); public int getid() { return this.id; public void setid(int i) { this.id = i; public String getdata() { return this.data; public void setdata(string d) { this.data public void persistcallback() { print( public void updatecallback() { print( u ); Slide 33

34 Puzzle #5 Callback public class ABean implements AnInterface punit ) EntityManager em; public void method1() { this.method2(); print( PreU ); AnEntity e = em.find(anentity.class, 5); e.setdata( newstring ); print( PostU ); private void method2() { print( PreP ); em.persist(new AnEntity(5)); print( PostP ); Slide 34

35 Puzzle #5 Callback AnInterface ejb; ejb.method1(); Answers a) PreP p p PostP PreU u u PostU b) PreP p PostP PreU PostU p u u c) PreP PostP PreU PostU p p u u d) An exception e) Depends on implementation f) None of the above Slide 35

36 Puzzle #5 Callback public class AnEntity int id; String data; public AnEntity() { public AnEntity(int id) { this.setid(id); public int getid() { return this.id; public void setid(int i) { this.id = i; public String getdata() { return this.data; public void setdata(string d) { this.data public void persistcallback() { print( public void updatecallback() { print( u ); Slide 36

Puzzle #5 Callback Chaos @Stateless public class ABean implements AnInterface { @PersistenceContext(unitName= punit ) EntityManager em; public void method1() { this.

37 Puzzle #5 Callback public class ABean implements AnInterface punit ) EntityManager em; public void method1() { this.method2(); print( PreU ); AnEntity e = em.find(anentity.class, 5); e.setdata( newstring ); print( PostU ); private void method2() { print( PreP ); em.persist(new AnEntity(5)); print( PostP ); Undefined whether PostPersist, PreUpdate, and PostUpdate occur immediately or at commit time Undefined whether PreUpdate and PostUpdate callbacks occur when entity is persisted and updated in the same tx Slide 37

38 Puzzle #5 Callback AnInterface ejb; ejb.method1(); Answers a) PreP p p PostP PreU u u PostU b) PreP p PostP PreU PostU p u u c) PreP PostP PreU PostU p p u u d) An exception e) Depends on implementation f) None of the above Slide 38

39 Puzzle #6 Interceptor AnInterface ejb; ejb.method1(); ejb.method2(); a) m1a m2 m1b m2 Answers b) INT m1a INT m2 m1b INT m2 c) INT m1a m2 m1b INT m2 d) An exception e) Depends on implementation f) None of the above Slide 39

40 Puzzle #6 Interceptor public class ABean implements AnInterface { public void method1() { print( m1a ); method2(); print( m1b ); public void method2() { print( m2 public Object imethod(invocationcontext ic) throws Exception { print( INT ); Slide 40

41 Puzzle #6 Interceptor AnInterface ejb; ejb.method1(); ejb.method2(); a) m1a m2 m1b m2 Answers b) INT m1a INT m2 m1b INT m2 c) INT m1a m2 m1b INT m2 d) An exception e) Depends on implementation f) None of the above Slide 41

Puzzle #6 Interceptor Ignominy @Stateless public class ABean implements AnInterface { public void method1() { print( m1a ); method2(); print( m1b ); public void method2() { print( m2 ); @AroundInvoke

42 Puzzle #6 Interceptor public class ABean implements AnInterface { public void method1() { print( m1a ); method2(); print( m1b ); public void method2() { print( m2 public Object imethod(invocationcontext ic) print( INT ); Missing call to ic.proceed() means intercepted method never executes Missing return will actually result in a compile error throws Exception { return ic.proceed(); Slide 42

43 Puzzle #6 Interceptor AnInterface ejb; ejb.method1(); ejb.method2(); a) m1a m2 m1b m2 Answers b) INT m1a INT m2 m1b INT m2 c) INT m1a m2 m1b INT m2 d) An exception e) Depends on implementation f) None of the above Slide 43

44 Puzzle #7 Iffy AnInterface ejb; ejb.method(100); Answers a) INT INT_1 INT_2 Num=100 b) INT_1 INT_2 Num=100 c) INT_1 INT_2 P_INT INT Num=101 d) P_INT INT INT_1 INT_2 Num=101 e) An exception f) None of the above Slide 44

45 Puzzle #7 Int2.class) public class ABean extends ParentClass implements AnInterface { public void method(int num) { print( Num= + public Object imethod(invocationcontext ic) throws Exception { print( INT ); return ic.proceed(); Slide 45

46 Puzzle #7 Iffy Interception public class ParentClass private Object imethod(invocationcontext ic) throws Exception { print( P_INT ); Object[] params = ic.getparameters(); Integer p = (Integer)(params[0]); params[0] = p + 1; ic.setparameters(params); return ic.proceed(); Slide 46

47 Puzzle #7 Iffy Interception public class Int1 public Object imethod(invocationcontext ic) throws Exception { print( INT_1 ); return ic.proceed(); public class Int2 public Object imethod(invocationcontext ic) throws Exception { print( INT_2 ); return ic.proceed(); Slide 47

48 Puzzle #7 Iffy AnInterface ejb; ejb.method(100); Answers a) INT INT_1 INT_2 Num=100 b) INT_1 INT_2 Num=100 c) INT_1 INT_2 P_INT INT Num=101 d) P_INT INT INT_1 INT_2 Num=101 e) An exception f) None of the above Slide 48

49 Puzzle #7 Int2.class) public class ABean extends ParentClass implements AnInterface { public void method(int num) { print( Num= + public Object imethod(invocationcontext ic) throws Exception { print( INT ); return ic.proceed(); Interceptor in bean always executes last in interceptor chain Slide 49

50 Puzzle #7 Iffy Interception public class ParentClass private Object imethod(invocationcontext ic) throws Exception { print( P_INT ); Object[] params = ic.getparameters(); Integer p = (Integer)(params[0]); params[0] = p + 1; ic.setparameters(params); return ic.proceed(); Non-session superclasses may define interceptor methods. They are called in order of hierarchy, top-most first Slide 50

$Puzzle #7 Iffy Interception public class Int1 { @AroundInvoke public Object imethod(invocationcontext ic) throws Exception { print( INT_1 ); return ic.$

51 Puzzle #7 Iffy Interception public class Int1 public Object imethod(invocationcontext ic) throws Exception { print( INT_1 ); return ic.proceed(); Interceptor classes called first, in order of declaration public class Int2 public Object imethod(invocationcontext ic) throws Exception { print( INT_2 ); return ic.proceed(); Slide 51

52 Puzzle #7 Iffy AnInterface ejb; ejb.method(100); Answers a) INT INT_1 INT_2 Num=100 b) INT_1 INT_2 Num=100 c) INT_1 INT_2 P_INT INT Num=101 d) P_INT INT INT_1 INT_2 Num=101 e) An exception f) None of the above Slide 52

53 Puzzle #8 Schizophrenic AnInterface ejb; ejb.method1(); ejb.method2(); ejb.method3(); return ejb.method4(); Answers a) AnEntity(5, String ) d) null b) AnEntity(5, NewString ) e) An exception c) AnEntity(5, ANewString ) f) None of the above Slide 53

54 Puzzle #8 public class ABean implements AnInterface punit ) EntityManagerFactory UserTransaction punit ) EntityManager em; public void method1() { tx.begin(); EntityManager em = emf.createentitymanager(); AnEntity e = new AnEntity(5); em.persist(e); e.setdata( String ); tx.commit(); em.close(); Slide 54

55 Puzzle #8 Schizophrenic Session public void method2() { AnEntity e = em.find(anentity.class, 5); tx.begin(); e.setdata( New + e.getdata()); tx.commit(); public void method3() { EntityManager em = emf.createentitymanager(); AnEntity e = em.find(anentity.class, 5); tx.begin(); e.setdata( A + e.getdata()); tx.commit(); em.close(); public AnEntity method4() { return em.find(anentity.class, 5); Slide 55

56 Puzzle #8 Schizophrenic AnInterface ejb; ejb.method1(); ejb.method2(); ejb.method3(); return ejb.method4(); Answers a) AnEntity(5, String ) d) null b) AnEntity(5, NewString ) e) An exception c) AnEntity(5, ANewString ) f) None of the above Slide 56

57 Puzzle #8 public class ABean implements AnInterface punit ) EntityManagerFactory UserTransaction punit ) EntityManager em; public void method1() { tx.begin(); EntityManager em = emf.createentitymanager(); AnEntity e = new AnEntity(5); em.persist(e); e.setdata( String ); tx.commit(); em.close(); Slide 57

jointransaction(); e.setdata( A + e.getdata()); tx.commit(); em.close(); public AnEntity method4() { return em.find(anentity.

58 Puzzle #8 Schizophrenic Session public void method2() { AnEntity e = em.find(anentity.class, 5); tx.begin(); e = em.find(anentity.class, 5); e.setdata( New + e.getdata()); tx.commit(); public void method3() { EntityManager em = emf.createentitymanager(); AnEntity e = em.find(anentity.class, 5); tx.begin(); em.jointransaction(); e.setdata( A + e.getdata()); tx.commit(); em.close(); public AnEntity method4() { return em.find(anentity.class, 5); Container-managed PC is scoped at tx, so result of find is detached, not managed Application-managed EM created outside tx is not synchronized with tx. Must explicitly call jointransaction(). Slide 58

59 Puzzle #8 Schizophrenic AnInterface ejb; ejb.method1(); ejb.method2(); ejb.method3(); return ejb.method4(); Answers a) AnEntity(5, String ) d) null b) AnEntity(5, NewString ) e) An exception c) AnEntity(5, ANewString ) f) None of the above Slide 59

60 Puzzle #9 Muddled AnInterface ejb; ejb.persist(); return ejb.method(); a) anentity(5, String, 100) b anentity(5, null, null) c) anentity(5, String, null) d) NullPointerException e) Some other exception Answers f) Depends on implementation Slide 60

61 Puzzle #9 Muddled public class ABean implements AnInterface punit ) EntityManager em; public void persist() { AnEntity e = em.persist(new AnEntity(5)); e.setsdata( String ); e.setintdata(100); public Object method() { return em.find(anentity.class,5); Slide 61

62 Puzzle #9 Muddled public class AnEntity int id; String sdata; Integer idata; public AnEntity() { public AnEntity(int id) { this.setid(id); public int getid() { return this.id; public void setid(int id) { this.id S_DATA ) public String getsdata() { return this.sdata; public void setsdata(string d) { this.sdata = I_DATA ) public Integer getintdata() { return this.idata; public void setintdata(int d) { this.idata = d; Slide 62

63 Puzzle #9 Muddled AnInterface ejb; ejb.persist(); return ejb.method(); a) anentity(5, String, 100) b anentity(5, null, null) c) anentity(5, String, null) d) NullPointerException e) Some other exception Answers f) Depends on implementation Slide 63

64 Puzzle #9 Muddled public class ABean implements AnInterface punit ) EntityManager em; public void persist() { AnEntity e = em.persist(new AnEntity(5)); e.setsdata( String ); e.setintdata(100); public Object method() { return em.find(anentity.class,5); Slide 64

Puzzle #9 Muddled Mappings @Entity public class AnEntity { int @Id id; int id; String sdata; Integer idata; Undefined to mix field annotations and property annotations.

65 Puzzle #9 Muddled public class AnEntity { id; int id; String sdata; Integer idata; Undefined to mix field annotations and property annotations. Must make them all use the same strategy. public AnEntity() { public AnEntity(int id) { public int getid() { return this.id; public void setid(int id) { this.id S_DATA ) public String getsdata() { return this.sdata; public void setsdata(string d) { this.sdata = I_DATA ) public Integer getintdata() { return this.idata; public void setintdata(int d) { this.idata = d; Slide 65

66 Puzzle #9 Muddled AnInterface ejb; ejb.persist(); return ejb.method(); a) anentity(5, String, 100) b anentity(5, null, null) c) anentity(5, String, null) d) NullPointerException e) Some other exception Answers f) Depends on implementation Slide 66

67 Puzzle #10 Cupid Cutting AnInterface ejb; Entity1 e = ejb.persist(); return ejb.query(e); Answers a) 4 d) 0 b) 3 e) An exception c) 1 f) None of the above Slide 67

68 Puzzle #10 Cupid Cutting public class Entity1 int Entity1 List<Entity1> List<Entity2> e2list; public Entity1() { public Entity1(int id) { this.id = id; public int getid() { return id; public List<Entity1> gete1list() { return e1list; public void sete1list(list<entity1> list) { e1list = list; Slide 68

69 Puzzle #10 Cupid Cutting public class Entity2 int Entity1 e1; public Entity2() { public Entity2(int id) { this.id = id; public int getid() { return id; public void sete1(entity1 entity) { e1 = entity; Slide 69

70 Puzzle #10 Cupid Cutting Corners <named-query name="entity1.entity1count"> <query>select COUNT(e1.e1List) FROM Entity1 e1 WHERE e1.id = :id </query> </named-query> <named-query name="entity1.entity2count"> <query>select COUNT(e1.e2List) FROM Entity1 e1 WHERE e1 = :entity1 </query> </named-query> Slide 70

71 Puzzle #10 Cupid Cutting public class ABean implements AnInterface punit ) EntityManager em; public Entity1 persist() { Entity1 a = new Entity1(1); Entity1 b = new Entity1(2); Entity1 c = new Entity1(3); Entity2 d = new Entity2(4); a.gete1list().add(a); a.gete1list().add(b); a.gete1list().add(c); em.persist(a); d.sete1(b); em.persist(d); return a; Slide 71

72 Puzzle #10 Cupid Cutting Corners public long query (Entity1 e) { long result1 = (Long)(em.createNamedQuery("Entity1.entity1Count").setParameter("id", e.getid()).getsingleresult()); long result2 = (Long) (em.createnamedquery("entity1.entity2count").setparameter("entity1", e).getsingleresult()); return result1 + result2; Slide 72

73 Puzzle #10 Cupid Cutting AnInterface ejb; Entity1 e = ejb.persist(); return ejb.query(e); Answers a) 4 d) 0 b) 3 e) An exception c) 1 f) None of the above Slide 73

74 Puzzle #10 Cupid Cutting Corners <named-query name="entity1.entity1count"> <query>select COUNT(e1.e1List) FROM Entity1 e1 WHERE e1.id = :id </query> </named-query> <named-query name="entity1.entity2count"> <query>select COUNT(e1.e2List) FROM Entity1 e1 WHERE e1 = :entity1 </query> </named-query> Slide 74

75 Puzzle #10 Cupid Cutting Corners public long query (Entity1 e) { long result1 = (Long)(em.createNamedQuery("Entity1.entity1Count").setParameter("id", e.getid()).getsingleresult()); long result2 = (Long) (em.createnamedquery("entity1.entity2count").setparameter("entity1", e).getsingleresult()); return result1 + result2; Slide 75

Puzzle #10 Cupid Cutting Corners @Entity public class Entity1 { @Id int id; @ManyToOne Entity1 e1; @OneToMany(mappedBy="e1", cascade=persist) List<Entity1> e1list; @OneToMany(mappedBy="e1")

76 Puzzle #10 Cupid Cutting public class Entity1 int Entity1 cascade=persist) List<Entity1> List<Entity2> e2list; public Entity1() { e1list = new ArrayList<Entity1>(); e2list = new ArrayList<Entity2>(); public Entity1(int id) { this(); this.id = id; OneToMany relationships are bidirectional so the other "mappedby" side must be specified in annotations Collections should be initialized if they are being used when creating new entities in memory Slide 76

77 Puzzle #10 Cupid Cutting public class Entity2 int Entity1 e1; public Entity2() { public Entity2(int id) { this.id = id; public int getid() { return id; public void sete1(entity1 entity) { e1 = entity; Slide 77

Puzzle #10 Cupid Cutting Corners @Stateless public class ABean implements AnInterface { @PersistenceContext(unitName= punit ) EntityManager em;

gete1list().add(a); a.gete1list().add(b); a.gete1list().add(c); em.persist(a); d.sete1(b); em.persist(d); return a; a.sete1(a); b.sete1(a); c.

78 Puzzle #10 Cupid Cutting public class ABean implements AnInterface punit ) EntityManager em; public Entity1 persist() { Entity1 a = new Entity1(1); Entity1 b = new Entity1(2); Entity1 c = new Entity1(3); Entity2 d = new Entity2(4); a.gete1list().add(a); a.gete1list().add(b); a.gete1list().add(c); em.persist(a); d.sete1(b); em.persist(d); return a; a.sete1(a); b.sete1(a); c.sete1(a); b.gete2list().add(d); Calling add() on an uninitialized List field will cause NPE Both sides of bidirectional relationships must be set Slide 78

79 Puzzle #10 Cupid Cutting AnInterface ejb; Entity1 e = ejb.persist(); return ejb.query(e); Answers a) 4 d) 0 b) 3 e) An exception c) 1 f) None of the above Slide 79

80 Summary EJB 3.0 and JPA are simple to use and can be quickly learned, but it's also a good idea to know the subtleties before attempting to use them in advanced or unusual ways. Slide 80

Links and Resources EJB 3.0 Reference Implementation http://glassfish.dev.java.net/javaee5 JPA Reference Implementation http://otn.oracle.com/jpa EJB 3.

81 Links and Resources EJB 3.0 Reference Implementation JPA Reference Implementation EJB 3.0 white papers, tutorials and resources Pro EJB 3: Java Persistence API Mike Keith & Merrick Schincariol (Apress) Slide 81

Module 8 The Java Persistence API

Module 8 The Java Persistence API Objectives Describe the role of the Java Persistence API (JPA) in a Java EE application Describe the basics of Object Relational Mapping Describe the elements and environment