Remote Interfaces

Client is remote

accesses EJB through the bean's remote interface and remote home interface.

• remote interface extends javax.ejb.EJBObject
• remote home interface extends javax.ejb.EJBHome
• all methods in EJB interface and EJB home interface must throw RemoteException as they are remote objects (invoked remotely by remote client).
• all method return types and argumetns in EJB and EJB interfaces must be only vaild RMI types like primitives, serializable objects and RMI/IIOP remote objects.
  

 

note: EJB uses Java RMI (Remote Method Invocation) over IIOP as the communication protocol.

Example Home Interface   public interface EnrollmentCartHome extends EJBHome {           EnrollmentCart create() throws CreateException, RemoteException; }

Example Component Interface public interface EnrollmentCart extends EJBObject {     public void addCourses(String[] courseIDs) throws RemoteException;     public Collection getCourses() throws RemoteException;     public void emptly() throws RemoteException; }

Example EJB class public class EnrollmentCartEJB implements javax.ejb.SessionBean { private SessionContect ctx; private HashSet cart; /* callback methods*/ public void setSessionContext(SessionContext ctx) { this.ctx = ctx; } public void ejbCreate() throws CreateException {   cart = new HashSet(); public void ejbActivate() {} public void ejbPassivate() {} public void ejbRemove() {} /*business methods*/ public void addCourses(String[] courseIds) {     if(courseIds == null) { return; }     for (int i=0; i<courseIDs.length; i++) {         cart.add(courseIds[i]); } } public Collection getCourses() { return cart; } public void empty() {cart.clear(); } }

Local Interfaces

Client is remote

accesses EJB through the bean's local interface and localhome interface.

• component interface extends javax.ejb.EJBLocalObject
• local home interface extends javax.ejb.EJBLocalHome
• requires client and EJB on same physical machine using same JVM..
• advantage: less network traffic, RMI call is expensive (involves stubs and skeletons marshalling and unmarshalling the call parameters, etc.).