JEST unifies REST and JPA for language neutral clients running in web browser or smart phone

1. JEST: REST on OpenJPA Pinaki Poddar, PhD Java Persistence Evangelist [email_address]

3. JEST: REST on OpenJPA JEST is RESTful interaction with OpenJPA Runtime http JDBC XML/JSON Java Object Graph

7. REST: RE presentational S tate T ransfer C0 C0 C1’ C1’ S1 S2 S1 renders C1 modifies C2 renders Response 1 Request 2 Request 1 Response 2 @ rest State Transition 1 2 3 4 5 6

10. JPA is Model-View-Controller for Persistence View Control Model /** * A persistent entity **/ @Entity public class Actor { @Id private String name ; } /** * Find Actor by name **/ public Actor findByName( String name ) { EntityManager em = …; return em.find( Actor . class , name); } POJO sees uses updates modifies Java Persistence API Relational Database

11. JPA: access-detach-merge programming model C0 C0 C1’ C1’ em1 em2 renders C1 modifies C2 renders State Transition SELECT … detach find merge commit UPDATE/INSERT/DELETE … 1 2 3 5 6 4

12. REST and JPA: brothers separated at birth? Stateless Server Detached Transaction Identifiable Resource Persistent Identity Coherent Representation Persistent Closure Self-descriptive JPA 2.0 Metamodel REST JPA

15. Identifiable Resource: URI for persistent object? Actor p1 = em1.find ( Actor . class , “ John ”); Actor p2 = em2.find ( Actor . class , “ John ”); name :” John ” hash : 56789 p1 name :” John ” hash : 56789 p2 p1.equals(p2) p1.hashCode() == p2.hashCode() p1 != p2 public class Actor { @Id String name ; } Persistent Identity carries the notion that both p1 and p2 refer to the same database record. EntityManager EntityManager … Robert … John ACTOR

17. OpenJPA Fetch Plan @Entity @FetchGroups ({ @FetchGroup ( name =&quot; OnlyName &quot;, attributes ={ @FetchAttribute ( name =&quot; firstName &quot;), @FetchAttribute ( name =&quot; lastName &quot;) }) }) public class Actor { @Id private String id ; private String firstName ; private String lastName ; private Gender gender ; private Date dob ; @OneToOne private Actor partner ; @OneToMany private Set<Movie> movies ; // getters and setters }

19. JPA Metamodel: Persistent Type System Class Type<X> ManagedType<X> BasicType<X> IdentifiableType<X> EmbeddableType<X> EntityType<X> MappedSuperclassType<X> package javax.persistence.metamodel package java.lang <X>: Type<X> represents Java class X

20. JPA Metamodel : Persistent Type System Field Attribute<X,Y> SingularAttribute<X,Y> PluralAttribute<X,C,E> ListAttribute<X,E> CollectionAttribute<X,E> SetAttribute<X> MapAttribute<X,K,V> package javax.persistence.metamodel package java.lang.reflect <X>: Attribute<X,Y> declared in Java class X <Y>: Attribute<X,Y> is of type Y <C>: PluralAttribute<X,C,E> is of Java collection type C <E>: PluralAttribute<X,C,E> contains elements of type E

21. JPA Metamodel: Persistent Scope java.lang.Class java.lang.reflect.Field Metamodel ManagedType<X> Attribute<X,Y> java.lang.ClassLoader A classloader defines a scope for a set of Java classes A metamodel defines a scope for a set of managed persistent types package javax.persistence.metamodel

24. JEST URI Syntax identifies JPA resources. maps to JPA operation decorates JPA operation JEST resolves argument strings to strong types, e.g. “ type=Actor ” to Actor .class . scheme authority path query context action qualifiers arguments OpenJPAEntityManager em = getPersistenceContext(); em.addFetchPlan(“ basic ”); Actor a = em.find( Actor . class , “m1”); find plan=basic type=Actor ? jest / / & id=m1 http 8080 openjpa.com / : ://

25. JEST URI Examples find an Actor with primary key m1 using fetch plan ‘basic’ http :// openjpa.com:8080 / jest / find / plan = basic ? type = Actor & m1 Query for a single Actor by name John http :// openjpa.com:8080 / jest / query / single ? q = select p from Actor p where p.name=:n & n = John Get the metamodel http :// openjpa.com:8080 / jest / domain

26. JEST translates HTTP verbs to JPA operations GET HTTP POST PUT DELETE find() getMetamodel() createQuery().getResultList() getProperties() /find / query / domain / properties merge() persist() remove() JEST Action JPA Operation non-transactional transactional

27. JEST Deployment < web-app > < servlet > < servlet-name > demo </ servlet-name > < servlet-class > demo.SimpleApp </ servlet-class > </ servlet > < servlet-mapping > < servlet-name > demo </ servlet-name > < url-pattern > /* </ url-pattern > </ servlet-mapping > <!-- Deployment descriptor for JESTServlet. --> < servlet > < servlet-name > jest </ servlet-name > < servlet-class > org.apache.openjpa.persistence.jest.JESTServlet </ servlet-class > < init-param > < param-name > persistence.unit </ param-name > < param-value > SimplePU </ param-value > </ init-param > </ servlet > < servlet-mapping > < servlet-name > jest </ servlet-name > < url-pattern > /jest/* </ url-pattern > </ servlet-mapping > </ web-app > Deployed as HTTP Servlet within the same module scope Identifies the module by persistence unit name

28. Deployment Modes for JEST Servlet JESTServlet emf Module X emf JESTServlet instantiates discovers instantiates or injected primary mode auxiliary mode default

36. JEST: JPA Detached Transaction C1 C1 C1’ C1’ S1 S2 S1 renders C1 modifies C2 renders A1 A1’ R1 Response 2 @ rest State Transition find() detach() represent() parse() merge() commit()

37. REST is successful in real world Success has many friends… “ Amazon has both SOAP and REST interfaces to their web services, and 85% of their usage is of the REST interface. ” Jeff Barr, Web Services Evangelist @ Amazon Reference: REST vs SOAP at Amazon

38. Does JEST pass the RESTness est? YES Q5 . Can server transfer logic to clients? NO Q4 . Can client determine the exact server endpoint? YES Q3 . Does response describe their cacheability for the client? NO Q2 . Does server store client context between requests? YES Q1 . Are clients separated from servers by a uniform interface?

39. Does JEST pass Uniform Interface Test? YES Q9 . Are related resources accessible via received representation? YES Q8 . Does representation carry enough information to be processed by the client? YES Q7 . Can client manipulate received resource representation? YES Q6 . Does request identify a resource?