Today's Objectives

1
Today's Objectives

• Overview of RMI
• Review how EJBs use RMI for communication

2
RMI/CORBA

• Internet Protocol enables passing data packets
  over the network.
• Transmission Control Protocol assembles the data
  packets into a continuous stream of data.
• Also, error checks and re-transmission.
• Socket, a combination of an IP address and port
  number that identifies a program, provides
  network
• data stream between two programs.
• Java Remote Method Protocol is the protocol for
  object communications (remote method invocation
• and parameter passing).
• Internet Inter-Orb Protocol is a language
  independent object communications protocol. A
  higher level
• protocol, GIOP, is used above IIOP for orb
  interoperability.

3
TCP/IP Socket

• try
• String ip_address "time_A.timefreq.bldrdoc.gov
  "
• Socket my_socket new Socket (ip_address, 13)
• BufferedReader my_input_stream new
  BufferedReader
• (new InputStreamReader (my_socket.getInputStream
  ()))
• String str my_input_stream.readLine()
• while (str ! null)
• System.out.println(str)
• str my_input_stream.readLine()
• catch (IOException e) System.out.println("Error"
  e)

4
RMI/CorbaStub and Skeleton for Dept EJB
Client
Remote Dept EJB
Skel
TCP/IP
5
Stubs and Skeletons

• Stub
• Initiates a connection with the remote VM
  containing the remote object
• Marshals (writes) the parameters to the remote VM
• Waits for the result of the method invocation
• Unmarshals (reads) the return value of exception
  returned
• Skeleton
• Unmarshals (reads) the parameters of the remote
  method
• Invokes the method on the actual remote object
  implementation
• Marshals (writes) the result (return value or
  exception) to the caller.
• Starting with Java 2 SDK, the actions of the
  stubs and skeletons are incorporated into JRMP
  stubs and skeletons are no longer generated
  separately.

6
Object Factory Pattern
Source Sun Microsystems
7
EJB Components

8
DeptHome Home Interface

• package GerlachPackage
• import javax.ejb.EJBHome
• import java.rmi.RemoteException
• import javax.ejb.CreateException
• import javax.ejb.FinderException
• import java.util.Collection
• public interface DeptHome extends EJBHome
• public Dept create() throws RemoteException,
  CreateException
• Dept create(long deptno) throws
  RemoteException, CreateException
• public Dept findByPrimaryKey(DeptPK primaryKey)
  throws RemoteException, FinderException
• public Collection findAll() throws
  RemoteException, FinderException

9
Dept -- Remote Interface

• package GerlachPackage
• import javax.ejb.EJBObject
• import java.rmi.RemoteException
• public interface Dept extends EJBObject
• long getDeptno() throws RemoteException
• void setDeptno(long newDeptno) throws
  RemoteException
• String getDname() throws RemoteException
• void setDname(String newDname) throws
  RemoteException
• String getLoc() throws RemoteException
• void setLoc(String newLoc) throws
  RemoteException

10
DeptBean Entity Bean

• package GerlachPackage.impl
• import javax.ejb.EntityBean
• import javax.ejb.EntityContext
• import GerlachPackage.DeptPK
• public class DeptBean implements EntityBean
• public EntityContext entityContext
• public long deptno
• public String dname
• public String loc
• public DeptPK ejbCreate(long deptno)
• this.deptno deptno
• return new DeptPK(deptno)
• public void setDeptno(long newDeptno)

11
Client

• public class SampleDeptClient1
• public static void main(String args)
• SampleDeptClient1 sampleDeptClient1 new
  SampleDeptClient1()
• try
• Hashtable env new Hashtable()
• env.put(Context.INITIAL_CONTEXT_FACTORY,
  "com.evermind.server.rmi.RMIInitialContextFactory"
  )
• env.put(Context.SECURITY_PRINCIPAL,
  "admin")
• env.put(Context.SECURITY_CREDENTIALS,
  "corbaisfun")
• env.put(Context.PROVIDER_URL,
  "ormi//javacr.cudenver.edu23791/jgerlach")
• Context ctx new InitialContext(env)
• DeptHome deptHome (DeptHome)ctx.lookup("De
  pt")
• // The initial context implements the Context
  interface and provides the starting point for
  resolution of names -- JNDI (Java Naming and
  Directory Interface).

12
Client Continued

• // Retrieve all instances using the findAll()
  method
• // (CMP Entity beans only)
• Dept dept
• Collection coll deptHome.findAll()
• Iterator iter coll.iterator()
• while (iter.hasNext())
• dept (Dept)iter.next()
• System.out.println("deptno "
  dept.getDeptno())
• System.out.println("dname "
  dept.getDname())
• System.out.println("loc "
  dept.getLoc())
• System.out.println()
• catch(Throwable ex) ex.printStackTrace()

13
Client Continued

• // Retrieve and modify single EJB instance
• dept deptHome.findByPrimaryKey(new DeptPK(10))
• System.out.println("deptno "
  dept.getDeptno())
• System.out.println("dname " dept.getDname())
• System.out.println("loc " dept.getLoc())
• dept.setLoc("Chicago")

14
Client Continued

• // Create a new dept EJB
• dept deptHome.create( 99 )
• dept.setDname("Systems")
• dept.setLoc("Denver")