Download Enterprise JavaBeans

Enterprise
JavaBeans
Dan Harkey
Client/Server Computing Program Director
San Jose State University
[email protected]
www.corbajava.engr.sjsu.edu
Session EJBs
Implement business logic that runs on an EJB
server
Are not shared between clients--logical extension of
a single client
Do not maintain persistent state
Two types
Stateless--no client specific state is maintained
between client method calls
Stateful--can maintain conversational state
Copyright 2001-2002, Dan Harkey. All rights reserved.
Page 1-2
Session EJB Component Contract
<<Interface>>
Serializable
<<Interface>>
EJBContext
(from io)
(from ejb)
<<Interface>>
EnterpriseBean
<<Interface>>
SessionSynchronization
(from ejb)
(from ejb)
getCallerPrincipal() : Principal
getEJBHome() : EJBHome
getRollbackOnly() : boolean
getUserTransaction() : UserTransaction
isCallerInRole(arg0 : String) : boolean
setRollbackOnly() : void
afterBegin()
afterCompletion()
beforeCompletion()
<<Interface>>
SessionBean
(from ejb)
<<Interface>>
SessionContext
ejbActivate()
ejbPassivate()
ejbRemove()
setSessionContext()
(from ejb)
getEJBObject()
Optional
YourSessionBean
ejbCreate()
businessMethod()
Session EJB Client/Server Contract
<<Interface>>
Remote
<<Interface>>
EJBMetaData
(from rmi)
<<Interface>>
EJBObject
(from ejb)
getEJBHome()
getHandle()
getPrimaryKey()
isIdentical()
remove()
<<Interface>>
YourRemoteInterface
businessMethod()
(from ejb)
getEJBHome()
getHomeInterfaceClass()
getPrimaryKeyClass()
getRemoteInterfaceClass()
isSession()
<<Interface>>
EJBHome
(from ejb)
<<Interface>>
Serializable
(from io)
getEJBMetaData()
getHomeHandle()
remove()
<<Interface>>
YourHomeInterface
<<Interface>>
Handle
<<Interface>>
HomeHandle
(from ejb)
(from ejb)
getEJBObject()
getEJBHome()
create()
Copyright 2001-2002, Dan Harkey. All rights reserved.
Page 3-4
EJB Development Process
The Count Stateless EJB
Copyright 2001-2002, Dan Harkey. All rights reserved.
Page 5-6
Count Stateless Session EJB
<<Interface>>
EJBHome
(from ejb)
<<Interface>>
SessionBean
(from ejb)
<<Interface>>
CountHome
(from statelessSession)
CountClient
(from statelessSession)
create()
CountEJB
(from statelessSession)
sum
main()
<<Interface>>
EJBObject
(from ejb)
CountEJB()
ejbCreate()
ejbActivate()
ejbPassivate()
ejbRemove()
setSessionContext()
increment()
<<Interface>>
Count
(from statelessSession)
increment()
Stateless Session EJB State Diagram
Copyright 2001-2002, Dan Harkey. All rights reserved.
Page 7-8
Count Stateless Session Interaction Diagram
: CountClient
JNDI :
InitialContext
EJB Home :
CountHome
EJB Object :
Count
EJB :
CountEJB
1: new()
2: lookup(JNDIHomeName)
3: new()
4: create()
5: new()
6: new()
7: setSessionContext(SessionContext)
8: ejbCreate( )
9: increment(sum)
10: increment(sum)
Home Interface for Stateless Session EJBs
Extends the EJBHome interface. It can also extend
other interfaces but must follow the
RMI-over-IIOP rules for interface definition
Declares one method named create which has no
parameters. The create method returns a reference
to a remote interface for the bean and throws
CreateException and RemoteException
Copyright 2001-2002, Dan Harkey. All rights reserved.
Page 9-10
Rules for Writing RMI-IIOP Interfaces
The interface must extend, either directly or
indirectly, the interface java.rmi.Remote. This
happens automatically for enterprise beans as the
EnterpriseBean interface extends java.rmi.remote
Each method declaration must satisfy the
requirements of a remote method declaration. These
requirements are:
A remote object declared as a parameter or return
value must be declared as a remote interface, not the
implementation class of that interface
Rules for Writing RMI-IIOP Interfaces
(continued)
Each method must throw RemoteException
Method parameters or return types must be a Java
object that is serializable. This includes Java
primitive types, remote Java objects, and non-remote
Java objects that implement the java.io.Serializable
interface.
A remote interface may also extend another
non-remote interfaces, as long as all of the methods
(if any) of the interface being extended satisfies the
requirements of a remote method declaration.
Copyright 2001-2002, Dan Harkey. All rights reserved.
Page 11-12
Count Stateless Session EJB: Home Interface
// CountHome.java
package count.statelessSession;
import javax.ejb.EJBHome;
import java.rmi.RemoteException;
import javax.ejb.CreateException;
public interface CountHome extends EJBHome
{
public Count create() throws RemoteException, CreateException;
}
Remote Interface for Stateless Session EJBs
Extends the EJBObject interface. It can also
extend other interfaces but again, it must follow the
RMI-over-IIOP rules for interface definition.
Declares the business methods the enterprise bean
will support. These methods must have valid
RMI-over-IIOP return types and arguments and
must declare RemoteException in addition to any
other exceptions thrown by the matching method in
the bean class.
Copyright 2001-2002, Dan Harkey. All rights reserved.
Page 13-14
Count Stateless Session EJB: Remote Interface
// Count.java
package count.statelessSession;
import javax.ejb.EJBObject;
import java.rmi.RemoteException;
public interface Count extends EJBObject
{
public int increment(int sum) throws RemoteException;
}
Class for Stateless Session EJBs
May extend other classes or interfaces but bean
class or one of it’s parent classes must implement
the SessionBean interface.
The class must be public and must not be abstract
or final.
It must provide a default, no-argument constructor
and it must not have a finalize method.
Copyright 2001-2002, Dan Harkey. All rights reserved.
Page 15-16
Class for Stateless Session EJBs (continued)
The bean class or one of it’s parent classes must
implement the ejbCreate method (note that
ejbCreate returns a void) and any business methods
declared in the remote interface.
The bean class can implement helper and private
methods that are not exposed to clients of the
enterprise bean.
Count Stateless Session EJB Class
// CountBean.java
package count.statelessSession;
import javax.ejb.*;
import java.rmi.RemoteException;
public class CountEJB implements SessionBean
{
// no arg contructor
public CountEJB() {}
public
public
public
public
public
void
void
void
void
void
ejbCreate() {}
ejbActivate() {}
ejbPassivate() {}
ejbRemove() {}
setSessionContext(SessionContext ctx ) {}
public int increment(int sum)
{
return ++sum;
}
}
Copyright 2001-2002, Dan Harkey. All rights reserved.
Page 17-18
Count Stateless Session EJB:
EJB Deployment Descriptor
<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE ejb-jar PUBLIC '-//Sun Microsystems, Inc.//DTD Enterprise
JavaBeans 1.1//EN' 'http://java.sun.com/j2ee/dtds/ejb-jar_1_1.dtd'>
<ejb-jar>
<description>no description</description>
<display-name>Ejb1</display-name>
<enterprise-beans>
<session>
<description>no description</description>
<display-name>CountStateless</display-name>
<ejb-name>CountStateless</ejb-name>
<home>count.statelessSession.CountHome</home>
<remote>count.statelessSession.Count</remote>
<ejb-class>count.statelessSession.CountEJB</ejb-class>
<session-type>Stateless</session-type>
<transaction-type>Bean</transaction-type>
</session>
</enterprise-beans>
</ejb-jar>
Count Stateless Session EJB:
Application Deployment Descriptor
<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE application PUBLIC '-//Sun Microsystems, Inc.//DTD J2EE
Application 1.2//EN' 'http://java.sun.com/j2ee/dtds/application_1_2.dtd'>
<application>
<display-name>CountStateless</display-name>
<description>Application description</description>
<module>
<ejb>ejb-jar27688.jar</ejb>
</module>
</application>
Copyright 2001-2002, Dan Harkey. All rights reserved.
Page 19-20
Count Stateless Session EJB:
J2EE RI Specific Deployment Descriptor
<?xml version="1.0" encoding="UTF-8"?>
<j2ee-ri-specific-information>
<server-name></server-name>
<rolemapping />
<enterprise-beans>
<ejb>
<ejb-name>CountStateless</ejb-name>
<jndi-name>statelessSessionCountHome</jndi-name>
</ejb>
</enterprise-beans>
</j2ee-ri-specific-information>
Steps Peformed by an EJB Client
Look up the enterprise bean’s home using JNDI
Create an instance of the bean
Call business methods on the bean
Remove the bean when it is no longer needed
Copyright 2001-2002, Dan Harkey. All rights reserved.
Page 21-22
Steps Performed to Look Up an EJB's Home
Interface Using JNDI
Creating an instance of the JNDI InitialContext
object
Call the lookup method of the InitialContext object
to find the bean’s home. A string name is passed to
the lookup method to identify the bean’s home
The object that is discovered using the lookup
method is cast to the correct type using the
narrow method of the PortableRemote object
Classes used by a JNDI Client
<<Interface>>
Context
(from naming)
InitialContext
(from naming)
InitialContext()
addToEnvironment()
bind()
close()
composeName()
createSubcontext()
destroySubcontext()
getEnvironment()
getNameInNamespace()
getNameParser()
list()
listBindings()
lookup()
lookupLink()
rebind()
removeFromEnvironment()
rename()
unbind()
Copyright 2001-2002, Dan Harkey. All rights reserved.
Page 23-24
Count Stateless Session EJB: Client (1 of 3)
// CountClient.java
package count.statelessSession;
import count.statelessSession.Count;
import count.statelessSession.CountHome;
// Count EJB Remote
// Count EJB Home
import java.rmi.*;
import java.util.*;
import java.io.*;
import javax.rmi.*;
import javax.naming.*;
import javax.ejb.*;
public class CountClient
{
public static void main ( String args[] )
{
int sum; // current sum
CountHome countHome;
Count Stateless Session EJB: Client (2 of 3)
try
{
// Get the initial JNDI context
System.out.println("Getting initial context");
InitialContext context = new InitialContext();
// Find the home interface and narrow to CountHome
Object object = context.lookup("statelessSessionCountHome");
countHome =
(CountHome)PortableRemoteObject.narrow(object, CountHome.class);
// Create EJB
System.out.println("Creating EJB");
Count count = countHome.create();
// Set sum to initial value of 0
System.out.println("Setting sum to 0");
sum = 0;
Copyright 2001-2002, Dan Harkey. All rights reserved.
Page 25-26
Count Stateless Session EJB: Client (3 of 3)
// Calculate Start time
long startTime = System.currentTimeMillis();
// Increment 1000 times
System.out.println("Incrementing");
for (int i = 0 ; i < 1000 ; i++ )
{ sum = count.increment(sum);
}
// Calculate stop time; print out statistics
long stopTime = System.currentTimeMillis();
System.out.println("Avg Ping = "
+ ((stopTime - startTime)/1000f) + " msecs");
System.out.println("Sum = " + sum);
} catch(Exception e)
{ System.err.println("Exception");
System.err.println(e);
}
}
Copyright 2001-2002, Dan Harkey. All rights reserved.
Page 27-28