5. Enterprise JavaBeans 5.4 Session Beans. Session beans

Transcription

1 5.4 Session Beans Session beans Exécutent des traitements métiers (calculs, accès BD, ) Peuvent accéder à des données dans la BD mais ne représentent pas directement ces données. Sont non persistants (short-lived) Peuvent être inclus dans une transaction Associés à un seul client Un flot d exécution est créé pour (en général) plusieurs appels de méthodes en provenance du même client et un état transactionnel est maintenu stateful session beans (avec état), ex: shopping cart chaque appel de méthode (sont des cas spéciaux des précédents) stateless session beans (sans état), pas de données interne, inutile de le rendre passif, peuvent être partagés par plusieurs clients, ex: fonctions mathématiques (tout ce dont la méthode a besoin est passé dans les paramètres) Détruits après un arrêt (ou une panne) du serveur EJB

2 5.4 Session Beans How a Client Uses a Session Bean JNDI Server Client lookup create method Home Container Bean Instance Component

3 5.4 Session Beans Stateless Session Beans Not tied to any particular client Can use instance variables only if they are not client related All Stateless Session Beans are equivalent A container can choose To serve the same instance of a Bean to multiple clients To serve different Bean instances to the same client at different times A container may maintain a pool of Stateless Session Beans No necessary relation between the moment when a client creates the Bean and when the Container creates the Bean Provide very high scalability

4 5.4 Session Beans Stateful Session Beans Assigned to a particular client Maintain per client state across multiple client requests May be passivated allows a degree of pooling The container serializes the state of a Bean non currently being used and writes state to secondary storage Frees JVM resources held for Bean When a new request arrives for Bean, it must be activated State read from secondary storage and deserialized Can only passivate a Bean if it is not in a transaction More on transactions later

5 5.4 Session Beans Lifecycle of a Stateful Session Bean Container Perspective Does Not Exist create remove Ready passivate activate Passive start transaction commit or rollback In Transaction timeout

6 5.5 Message Driven Beans Message Driven Bean Traitements métiers asynchrones Messages JMS déclenchent le traitement Files d'attente de messages Supportent mieux la montée en charge Stateless bean Désanvantages : Une seule méthode onmessage() Très récents. Evoluent encore.

7 5.5 Message Driven Beans Message Beans Executes upon receipt of a client JMS message Asynchronous No return value Stateless and short lived May access persistent data but does not represent persistent data Not tied to a client A single Message Bean can process messages from multiple clients Has neither Home nor Component interface Client Destination Msg Bean Msg Bean Instance Msg Bean Instance Instance

8 Summary Characteristics of EJBs Contain business logic that operates on enterprise s data Bean provider defines a client view Client view is independent of the container in which the bean is deployed Beans are created and managed at runtime by a Container which mediates client access Client never directly accesses the Bean Since container involved in path between client and Bean instance it can implement pragmatics and lifecycle functions If Bean uses only services defined by EJB Spec., it can be deployed in any compliant Container Specialized containers with extended functionality can be defined Can be assembled into an application without requiring source code

9 Putting It Alltogether 1. Show how to implement an entity bean (Cabin) 2. Show how to implement a client application using this entity bean 3. Show how to implement a session bean (TravelAgent) 4. Show how to implement a client application using these beans 5. Show how to deploy the bean:.jar file (packaging) XML deployment descriptor

10 The Remote Interface package com.titan.cabin; import java.rmi.remoteexception; public interface CabinRemote extends javax.ejb.ejbobject public String getname() throws RemoteException; public void setname(string str) throws RemoteException; public int getdecklevel() throws RemoteException; public void setdecklevel(int level) throws RemoteException; public int getshipid() throws RemoteException; public void setshipid(int sp) throws RemoteException; public int getbedcount() throws RemoteException; public void setbedcount(int bc) throws RemoteException;

11 The Local Interface package com.titan.cabin; import java.rmi.remoteexception; java.ejb.ejbexception; CabinLocal public interface CabinRemote extends javax.ejb.ejbobject EJBLocalObject public String getname() throws RemoteException; EJBException; public void setname(string str) throws RemoteException; EJBException; public int getdecklevel() throws RemoteException; EJBException; public void setdecklevel(int level) throws RemoteException; EJBException; public int getshipid() throws RemoteException; EJBException; public void setshipid(int sp) throws RemoteException; EJBException; public int getbedcount() throws RemoteException; EJBException; public void setbedcount(int bc) throws RemoteException; EJBException;

12 The Local Interface (2) package com.titan.cabin; import javax.ejb.ejbexception; public interface CabinLocal extends javax.ejb.ejblocalobject public String getname() throws EJBException; public void setname(string str) throws EJBException; public int getdecklevel() throws EJBException; public void setdecklevel(int level) throws EJBException; public int getshipid() throws EJBException; public void setshipid(int sp) throws EJBException; public int getbedcount() throws EJBException; public void setbedcount(int bc) throws EJBException;

13 TheRemoteHome Interface package com.titan.cabin; import java.rmi.remoteexception; import javax.ejb.createexception; import javax.ejb.finderexception; public interface CabinHomeRemote extends javax.ejb.ejbhome public CabinRemote create(integer id) throws CreateException, RemoteException; public CabinRemote findbyprimarykey(integer pk) throws FinderException, RemoteException;

14 The Local Home Interface package com.titan.cabin; import java.rmi.remoteexception; import javax.ejb.createexception; import javax.ejb.finderexception; CabinHomeLocal javax.ejb.ejbexception; javax.ejb.ejblocalhome public interface CabinHomeRemote extends javax.ejb.ejbhome public CabinRemote create(integer id) throws CreateException, RemoteException; EJBException; public CabinRemote findbyprimarykey(integer pk) throws FinderException, RemoteException; EJBException;

15 The Local Home Interface (2) package com.titan.cabin; import java.rmi.ejbexception; import javax.ejb.createexception; import javax.ejb.finderexception; public interface CabinHomeLocal extends javax.ejb.ejblocalhome public CabinLocal create(integer id) throws CreateException, EJBException; public CabinRemote findbyprimarykey(integer pk) throws FinderException, EJBException;

16 The Bean Class Create methods Business methods package com.titan.cabin; import javax.ejb.entitycontext; import javax.ejb.createexception; public abstract class CabinBean implements javax.ejb.entitybean public Integer ejbcreate(integer id) throws CreateException this.setid(id); return null; public void ejbpostcreate(integer id) public abstract void setid(integer id); public abstract Integer getid(); public abstract void setshipid(int ship); public abstract int getshipid(); public abstract void setname(string name); public abstract String getname(); public abstract void setbedcount(int count); public abstract int getbedcount(); public abstract void setdecklevel(int level); public abstract int getdecklevel(); Life-cycle callback methods from EntityBean public void setentitycontext(entitycontext ctx) // Not implemented. public void unsetentitycontext() // Not implemented. public void ejbactivate() // Not implemented. public void ejbpassivate() // Not implemented. public void ejbload() // Not implemented. public void ejbstore() // Not implemented. public void ejbremove() // Not implemented.

17 Using the Remote Client API package com.titan.clients; import com.titan.cabin.cabinhomeremote; import com.titan.cabin.cabinremote; import javax.naming.initialcontext; import javax.naming.context; import javax.naming.namingexception; import javax.rmi.portableremoteobject; import java.rmi.remoteexception; public class Client_1 public static void main(string [] args) try Context jndicontext = new InitialContext(); Object ref = jndicontext.lookup("cabinhomeremote"); CabinHomeRemote home = (CabinHomeRemote) PortableRemoteObject.narrow(ref,CabinHomeRemote.class); CabinRemote cabin_1 = home.create(new Integer(1)); cabin_1.setname("master Suite"); cabin_1.setdecklevel(1); cabin_1.setshipid(1); cabin_1.setbedcount(3); CabinRemote cabin_2 = home.findbyprimarykey(new Integer(1)); System.out.println(cabin_2.getName()); System.out.println(cabin_2.getDeckLevel()); System.out.println(cabin_2.getShipId()); System.out.println(cabin_2.getBedCount()); catch (java.rmi.remoteexception re)re.printstacktrace(); catch (javax.naming.namingexception ne)ne.printstacktrace(); catch (javax.ejb.createexception ce)ce.printstacktrace(); catch (javax.ejb.finderexception fe)fe.printstacktrace();

18 Using the Local Client API package com.titan.clients; import com.titan.cabin.cabinhomeremote; import com.titan.cabin.cabinremote; import javax.naming.initialcontext; import javax.naming.context; import javax.naming.namingexception; import javax.rmi.portableremoteobject; import java.rmi.remoteexception; public class Client_1 public static void main(string [] args) try Context jndicontext = new InitialContext(); Object ref = jndicontext.lookup("java:comp/env/ejb/cabinhomelocal"); CabinHomeLocal home = (CabinHomeLocal)ref; CabinLocal cabin_1 = home.create(new Integer(1)); cabin_1.setname("master Suite"); cabin_1.setdecklevel(1); cabin_1.setshipid(1); cabin_1.setbedcount(3); Integer pk = new Integer(1); CabinLocal cabin_2 = home.findbyprimarykey(pk); System.out.println(cabin_2.getName()); System.out.println(cabin_2.getDeckLevel()); System.out.println(cabin_2.getShipId()); System.out.println(cabin_2.getBedCount()); catch (javax.naming.namingexception ne)ne.printstacktrace(); catch (javax.ejb.createexception ce)ce.printstacktrace(); catch (javax.ejb.finderexception fe)fe.printstacktrace(); The same as in the remote client, except that home.findbyprimarykey(pk) returns a CabinLocal instead of a CabinRemote

19 Entity Beans creation and removal Image tirée du livre Enterprise Java Beans, R. Monson-Haefel, O'Reilly

20 The Remote Interface package com.titan.travelagent; import java.rmi.remoteexception; import javax.ejb.finderexception; public interface TravelAgentRemote extends javax.ejb.ejbobject // String elements follow the format "id, name, deck level" public String [] listcabins(int shipid, int bedcount) throws RemoteException; Thechanges for thelocal interface are analogous to the example with the entity bean (extends javax.ejb.ejblocalobject, throws EJBException)

21 TheRemoteHome Interface package com.titan.travelagent; import java.rmi.remoteexception; import javax.ejb.createexception; public interface TravelAgentHomeRemote extends javax.ejb.ejbhome public TravelAgentRemote create() throws RemoteException, CreateException; The changes for the local home interface are analogous to the example with the entity bean (extends javax.ejb.ejblocalhome, throws EJBException)

22 The Bean Class package com.titan.travelagent; import com.titan.cabin.cabinremote; import com.titan.cabin.cabinhomeremote; import java.rmi.remoteexception; import javax.naming.initialcontext; import javax.naming.context; import javax.ejb.ejbexception; import java.util.vector; public class TravelAgentBean implements javax.ejb.sessionbean public void ejbcreate() // Do nothing. Create method // String elements follow the format "id, name, deck level" public String [] listcabins(int shipid, int bedcount) try javax.naming.context jndicontext = new InitialContext(); Object obj = jndicontext.lookup("java:comp/env/ejb/cabinhomeremote"); CabinHomeRemote home = (CabinHomeRemote) javax.rmi.portableremoteobject.narrow(obj,cabinhomeremote.class); The single business method for (int i = 1; ; i++) Integer pk = new Integer(i); CabinRemote cabin = null; try cabin = home.findbyprimarykey(pk); catch(javax.ejb.finderexception fe) System.out.println("Caught exception: "+fe.getmessage()+" for pk="+i); break; // Check to see if the bed count and ship ID match. if (cabin!= null && cabin.getshipid() == shipid && cabin.getbedcount() == bedcount) String details = i+","+cabin.getname()+","+cabin.getdecklevel(); vect.addelement(details); String [] list = new String[vect.size()]; vect.copyinto(list); return list; catch(exception e) throw new EJBException(e); Vector vect = new Vector(); Beans are clients to other beans, just like applications and must interact with other beans in the same way that the client applications interact with beans. (i.e. first locate and obtain a reference to the bean's EJB home using JNDI) public void ejbremove() public void ejbactivate() public void ejbpassivate() public void setsessioncontext(javax.ejb.sessioncontext cntx) Life-cycle callback methods for session bean

23 Client Application package com.titan.clients; import com.titan.travelagent.travelagenthomeremote; import com.titan.travelagent.travelagentremote; import javax.naming.initialcontext; import javax.naming.context; import javax.naming.namingexception; import javax.ejb.createexception; import javax.rmi.portableremoteobject; import java.rmi.remoteexception; public class Client_3 public static int SHIP_ID = 1; public static int BED_COUNT = 3; // Get a list of all cabins on ship 1 with a bed count of 3. String list [] = travelagent.listcabins(ship_id,bed_count); for(int i = 0; i < list.length; i++) System.out.println(list[i]); catch(java.rmi.remoteexception re) re.printstacktrace(); catch(throwable t) t.printstacktrace(); public static void main(string [] args) try Context jndicontext = new InitialContext(); Object ref = jndicontext.lookup("travelagenthomeremote"); TravelAgentHomeRemote home = (TravelAgentHomeRemote) PortableRemoteObject.narrow(ref,TravelAgentHomeRemote.class); TravelAgentRemote travelagent = home.create(); The changes for a local client are analogous to the example with the entity bean (no need to narrow() and no RemoteExceptions)

24 Session Beans creation and removal Image tirée du livre Enterprise Java Beans, R. Monson-Haefel, O'Reilly

25 Deploying the bean Before deploying an entity bean you need to define (XML deployment descriptor file) your abstract persistence model, which links: the bean to a database table; and the properties to attributes (columns) The table should either already exist, or it is generated by the container.

26 The JAR file Package all the classes and interfaces associated with a bean, including the deployment descriptor, into one file. The deployment descriptor file must be called ejb-jar.xml and must be in a META-INF subfolder. The name of the jar file is not relevant. It is this jar file that is actually deployed in the container, following the instructions of the container vendor. Note that the Cabin_Object, CabinRemote_Stub, CabinRemoteHome_Stub, TravelAbent_Object, TravelAgentRemote_stub, TravelAgentHomeRemote_stub are all generated by the container at deployment time. titan.jar META-INF com ejb-jar.xml jboss.xml titan cabin CabinRemote.class CabinBean.class CabinHomeRemote.class travelagent TravelAgentRemote.class TravelAgentBean.class TravelAgentHomeRemote.class