1. Presentation Outline of Commercial Systems
• Bahman
Part A: Java Beans
Part B: Enterprise Java Beans
• John
Corba
OLE
ActiveX
• Andrew
COM
DCOM
COM+

2. Java Beans & Enterprise Java Beans
Component-Based Design
Bahman Kalali
Computer Systems Group
bkalali@csg.uwaterloo.ca
Spring 2002

3. Outline (Part A)
 Introduction to JavaBeans
 A Bean's Public Interface
 Bean Properties
 Bean Events
 Bean Methods
 Reflection API
 Bean Distribution
 Summary

4. Java Bean is a reusable platform-neutral software component that
can be visually manipulated in a visual application builder tool.
This definition has two distinct parts:
 A bean is a software component.
 A bean can be visually manipulated in a tool.
Introduction

5. Construction from Components

6.  Properties
 Methods
 Events
A Bean's Public Interface

7. At the source code level, a bean's property is nothing more than a
private attribute of a class that is supported by public getter and/or setter
methods.
Type of Properties
 Simple
 Boolean
 Index
 Bound
 Constrained
Bean’s Properties

8. Sample Account Property Balance

9.  Naming convention to expose a simple property:
public void setXxx (<type> arg)
public <type> getXxx()
 Example for Account's balance property:
public void setBalance( int amount )
public int getBalance()
By applying a naming pattern to the set/get Balance methods above,
the visual builder tool will expose a read/write "balance" property that
has the type int.
Exposing Simple Properties

10.  Naming convention to expose a boolean property:
public void setXxx (boolean arg)
public boolean isXxx()
 Example for overdrawn property:
public void setOverdrawn( boolean overdrawn )
public boolean isOverdrawn()
Boolean properties may be exposed by using the isXxx naming convention.
Exposing Boolean Properties

11.  Naming convention to expose an indexed property:
public void setXxx ( <type> [] arg)
public <type>[] getXxx()
public void setXxx (int index, <type> arg)
public <type> getXxx (int index)
 Example for an Account owner property:
public void setOwner(String[] owners)
public String getOwner()
public void setOwner(int index, String owner)
public String getOwner(int index)
Exposing Indexed Properties

12. // Account Class - non visual Java Bean
public class Account extends Object {
int balance = 0;
public Account() { // constructor }
public void setBalance ( int newBalance ) { balance = newBalance; }
public int getBalance() { return balance; }
public void deposit ( int pennies ) { setBalance ( getBalance() + pennies ); }
public void withdraw ( int pennies ) { setBalance ( getBalance() - pennies ); }
}
// end of class Account
Account Bean with a balance Property

13. Bound Properties
• A Bean properties changes, another Bean may want to be notified of the
change and react to the change.
• Whenever a bound properties changes, notification of change is sent to
interested listeners.
• It is up to the source Bean to keep track of listeners.

14. Account Bean with a Balance Property
• PropertyChangeSupport object constructs a PropertyChangeEvent object
and passes it to the Listener chain.
• Listener objects will interrogate the property that is changing and process
accordingly.

15. Constrained Properties
1) setBalance called
2) Account notifies the VetoableChangeListeners
of pending change request
3) Listeners can optionally throw exception
4) balance is updated if no exception is thrown

16. Bean Custom Events
• Bound and constrained properties fire events when properties are changed.
• Java Beans can also fire other kind of events (custom events).
• The application developer can wire up to these events without writing code.

17.  Naming conventions are used
public void addXxxListener ( XxxListener listener)
public void removeXxxListener ( XxxListener listener)
 Example for exposing an OverdrawEvent
public void addOverdrawListener ( OverdrawListener listener)
public void removeOverdrawListener ( OverdrawListener listener)
 In addition to these methods, the source object also provides:
1) OverdrawEvent class
2) OverdrawListener interface
3) code to fire the event
4) code to manage the listener chain
Exposing Bean Custom Events

18. Bean Methods
• To expose a method in the Bean’s public interface, simply make the method
public.

19. How does a visual Builder tool determines
a Bean’s public interface?
• At development time the visual builder tool is able to
interrogate beans, and figure out what's in there.
• How does it do that?  The Java Reflection API

20. In Java 1.1 and higher, anyone can inspect a class using the
Reflection API
Account account = new Account();
Class classObject = account.getClass();
Method [] methodsArray = classObject.getDeclaredMethods();
methodsArray now contains an array of Method objects for the class
Account
A method objects contain information about a method's:
 Method name
 Return type
 Argument list
 Access type
Reflection API

21.  Beans can be distributed in a JAR file (basically a ZIP file).
 The JAR utility that comes with the JDK can be used to create JAR files.
 JAR files can contain any type of file, not just Java bytecodes,
image,sound and text.
 A manifest file describes the contents of the JAR.
Bean Distribution

22.  Beans
 are software components
 are usable by programming tools
 are packaged in JAR files
 use a standard naming convention
 have a public interface
 A Bean's Public Interface composed of:
 Properties
 Simple
 Indexed
 Boolean
 Bound
 Constrained
 Events
 Signalled by changing properties
 Signalled for custom state change
 Methods
 Default is any public method
Summary

23.  Introduction to Enterprise Java Beans
 Three-Tiered Architecture
 JBoss Application Server
 Enterprise Java Beans
 Accessing a Business Method
 Case Study: Distributed Shoe Web Application
 Demonstration of application lifecycle
 Summary
23
Outline (Part B)

24.  EJB specification defines an architecture for the development
and deployment of transactional, distributed object applications-
based, server-side software components.
 Case Study
 Shoe Retailer Company
24
ShoeCollection
Shoe
brand
branch
name
id
quantities
25 Running Montreal Nike 50
Introduction

25.  Client Layer
 Presentation Layer
 Business Logic Layer
 Data Layer
Client Layer
Presentation
Layer
Business Logic
Layer
Data Layer
Logical Layers Typical Web
Implementation
Browser
Database
Application Server
Web Server
Lower Tier
Upper Tier
Middle Tier
25
Three-Tiered Architecture
EJB
Java Beans

26.  JBoss is an application server written in Java that can host EJB
component.
 JBoss provides a container.
 An EJB container implicitly manages resources for EJB:
 Threads
 Socket
 Database connections
 Remote accessibility
 Mutliclient support
 Persistence management
26
JBoss Application Server

27. Bean Types
 Session Beans => models business processes
 Entity Beans => models business data
Application Server
EJB Container
Session Bean
Entity Bean
JSP/Java Beans Servlet
Browser
DB
Web Server
Presentation
Layer
Business Logic
Layer
Enterprise Java Beans

28. EJB
Home Object
EJB
Object Bean Class
Home
Interface
Remote
Interface
Client
EJB
Home Object
EJB
Object
EJB Container
JBoss Application Server
Client
Enterprise Java Beans (contd.)
Enterprise Bean Components composed of:
 (1) Bean Class ( i.e. ShoeBean.java)
 (5) Home Interface ( i.e. ShoeHome.java)
 (3) Remote Interface ( i.e. Shoe.java)
 (2) EJB Object
 (4) EJB Home Object( Responsibility: Create, Find, Remove EJB object)
 (6) Deployment Descriptor( i.e ejb-jar.xml)

29. Retrieval of the Home object reference and generation of
remote EJB object reference.
EJB Object
Remote Interface
Home Interface
EJB Container
Client Code
Enterprise Bean
JNDI
Home Object
1: Retrieve
reference
2: Return Home
Object reference
3: Request new
EJB object
Home Object
5: Return EJB object reference
4: Create EJB object
Directory Service
29
Accessing a Business Method

30.  Handling a client request to a business method.
EJB Object
Remote Interface
Home Interface
EJB Container
EJB Object
EJB Object
Home Object
Client Code
1:Call a Method
4: Return
value to client
Enterprise Bean
2: Acquire a Bean, and delegate
the method to the Bean
3:Method Returns
30
Accessing a Business Method (cont’d.)

31. Presentation
Layer
Business Logic
Layer
Client Layer
Data Layer
JspShoeBrowse
Java Bean
JSP Pages
ShoeCollection
Session Bean
Shoe
Entity Bean
Web Browser
Tomcat Web Server
JBoss Application Server
<<HTTP>>
<<RMI>>
EJB Container
Servlet Container
Hypersonic database
31
Shoe Distributed Web Application

32.  Build
 Package
 Deploy
 Run
cs854-WebServer
WEB-INF
classes
lib
JspShoeBrowse.class
browse.jsp
prev.jsp
mext.jsp
search.jsp
header.html
footer.html
shoe.jar
web.xml
shoe.war
cs854-ApplicationServer
shoe
Shoe.class
ShoeHOME.class
ShoeBean.class
ShoeCollection.class
ShoeCollectionHome.class
ShoeCollectionBean.class
shoecollection
utils
ShoeExistsException.class
jboss.xml
ejb-jar.xml
META-INF
shoe.jar
32
Demonstration of application lifecycle

33. 33
JavaBeans Enterprise JavaBeans
JavaBeans may be visible or
nonvisible at runtime.
An EJB is a non-visual, remote object.
JavaBeans are intended to be local to a
single process and are primarily
intended to run on the client side.
EJBs are remotely executable
components or business objects that
can be deployed only on the server.
JavaBeans is a component technology
to create generic Java components that
can be composed together into applets
and applications.
Even though EJB is a component
technology, it neither builds upon nor
extends the original JavaBean
specification.
JavaBeans are not typed. EJBs are of two types—session beans
and entity beans.
No explicit support exists for
transactions in JavaBeans.
EJBs may be transactional and the EJB
Servers provide transactional support.
Summary

34. CORBA Key Concepts
• Com+mon Object Request Broker Architecture
• Location Transparency
• Objects
• Portable
• Standard

35. Simplified Architecture
• Interface Definition Language(IDL)
• Application Programming Interface(API)
• Object Request Broker(ORB)

36. CORBAArchitecture
Dyn.
Inter-
face
IDL
Stub
ORB
Interface
IDL
Skeleton
Object
Adapter
Object Implementation
Client
Object Services: naming, events, life cycle, persistence, transactions,
concurrency, relationships, externalization, object licensing,
properties, object query.
ORB
OS Kernel OS Kernel
Network

37. IDL Interface for Quoter
interface Stock {
double price ();
readonly attribute string symbol;
readonly attribute string full_name;
};
interface Stock_Factory {
Stock get_stock (in string stock_symbol)
raises (Invalid_Stock_Symbol);
};

38. In client.cpp:
int main (int argc, char* argv[])
{
try {
// First initialize the ORB, that will remove some arguments...
CORBA::ORB_var orb =
CORBA::ORB_init (argc, argv,
"" /* the ORB name, it can be anything! */);
// Get Reference to desired object
// call methods to access object
orb->destroy ();
}
catch (CORBA::Exception &ex) {
std::cerr << "CORBA exception raised!" << std::endl;
}
return 0;
}
Client - Manage ORB in Stock Quoter
Client.cpp

39. Client - Get Quoter
Object R
In client.cpp:
#include "QuoterC.h”
CORBA::Object_var factory_object = orb->string_to_object(argv[1]);
Quoter::Stock_Factory_var factory =
Quoter::Stock_Factory::_narrow (factory_object.in ());
for (int i = 2; i != argc; ++i)
{
try {
// Get the stock object
Quoter::Stock_var stock = factory->get_stock (argv[i]);
Client.cpp

40. ef

41. Implement Get_Stock
Method
In stock_factory_i.cpp
// Return Object Reference
Quoter::Stock_ptr Quoter_Stock_Factory_i::get_stock
(const char *symbol)
throw (Quoter::Invalid_Stock_Symbol)
{
if (strcmp (symbol, "RHAT") == 0)
{ return this->rhat_._this(); }
else if (strcmp (symbol, "MSFT") == 0)
{ return this->msft_._this (); }
throw Quoter::Invalid_Stock_Symbol ();
}
Stock_
Factory_i.cpp

42. Implementing Stock Interface
In stock_i.cpp
// Access object
class Quoter_Stock_i : public POA_Quoter::Stock
{
public:
Quoter_Stock_i (const char *symbol, const char*full_name,
CORBA::Double price);
private:
std::string symbol_;
std::string full_name_;
CORBA::Double price_;
};
Stock_i.cpp

43. Stock Operations
and Attributes
In stock_i.cpp:
// Access object
class Quoter_Stock_i : public POA_Quoter::Stock
{
public: // some details omitted
char *symbol () throw (CORBA::SystemException);
char *full_name () throw (CORBA::SystemException);
CORBA::Double price () throw (CORBA::SystemException);
};
// In the .cpp file:
char * Quoter_Stock_i::symbol () throw
(CORBA::SystemException)
{ return CORBA::string_dup (this->symbol_.c_str ());
}
Stock_i.cpp

44. Implement
Server
int main (int argc, char* argv[])
{
try
{ // First initialize the ORB, that will remove some arguments…
CORBA::ORB_var orb = CORBA::ORB_init (argc, argv, "" /* the ORB name, it
can be anything! */);
CORBA::Object_var poa_object =
orb->resolve_initial_references ("RootPOA");
PortableServer::POA_var poa =
PortableServer::POA::_narrow (poa_object.in ());
PortableServer::POAManager_var poa_manager =
poa->the_POAManager ();
poa_manager->activate ();
// The application code goes here!
// Destroy the POA, waiting until the destruction terminates
poa->destroy (1, 1); orb->destroy ();
}
catch (CORBA::Exception &ex) { std::cerr << "CORBA exception raised!" <<
std::endl; } return 0; }
Server.cpp

45. •CORBA provides a communication
infrastructure for a heterogeneous, distributed
collection of collaborating objects
•Analogous to “hardware bus”
Software Bus

47. OLE Overview
• Object Linking and Embedding
• Microsoft 's technology for supporting compound documents
• A way for Windows to create documents containing objects from
other programs.
• Components can be re-used by many applications (referred to
as component containers).

48. OLE Example
• Pie chart generated by Excel
embedded in a word
document being displayed in
a PowerPoint presentation..

49. OLE Technology
• A set of APIs to create and display a (compound) document
• The Component Object Model (COM) now takes in OLE as part
of a larger concept. It has become a set of standard COM
interfaces
• Embedded documents retain all their original properties. If the
user decides to edit the embedded data, Windows activates the
originating application and loads the embedded document.

50. OLE Extensions
• Automation is an OLE technology, which enables third party
applications to remotely control Office applications.
• e.g. Puppeteer invokes Automation interfaces to modify
application behavior when executing on bandwidth limited
platforms.
• using Automation interfaces, Puppeteer can act as a buffer for a
large PowerPoint presentation, loading slides while the user
presents.

51. ActiveX - Overview
• A loosely-defined set of technologies developed by Microsoft, ActiveX is
an outgrowth of two other Microsoft technologies called OLE (Object
Linking and Embedding) and COM (Component Object Model). ActiveX
applies to a whole set of COM-based technologies.
• ActiveX control is Microsoft 's answer to the Java technology from
. An ActiveX control is roughly equivalent to a applet, but is
known as an ActiveX control.
• Writing a program to run in the ActiveX environment creates a self-
sufficient program that can be run anywhere in your ActiveX network
• This component is known as an ActiveX control, and is often used to
attach a program to a web page.

52. ActiveX - Implementation
• An ActiveX control can be created using one of several
languages or development tools, including C++ and Visual
Basic, or PowerBuilder, or with scripting tools such as VBScript.
• Currently, ActiveX controls run in 95/98/NT/2000 and in
. Microsoft plans to support ActiveX controls for
UNIX.
• Similar (but different) security issues as applets

53. Example
Sub
()
Resp = Window.Confirm "Use the MS Agent?"
If Resp Then
Window.Alert "Loading ActiveX Controls."
Document.WriteLn "<OBJECT ID='Agent' width=0 height=0"
Document.WriteLn "CLASSID='CLSID:F5BE8BD2-7DE6-11D0-91FE-
00C04FD701A5'"
Document.WriteLn " CODEBASE='http://activex.microsoft.com/" & _
"controls/agent/msagent.exe#VERSION=1,5,1,0'>"
Document.WriteLn "<" & Chr(47) & "OBJECT>"
Document.WriteLn "<OBJECT ID='TruVoice' width=0 height=0"
Document.WriteLn " CLASSID='CLSID:B8F2846E-CE36-11D0-AC83-
00C04FD97575'"
Document.WriteLn " CODEBASE='http://activex.microsoft.com/" & _
"controls/agent/cgram.exe#VERSION=1,5,0,0'>"
Document.WriteLn "<" & Chr(47) & "OBJECT>"
End If
End Sub

54. Commercial Products :
Microsoft COM/DCOM/COM+
Andrew Trevors
Software Architecture Group
adtrevor@uwaterloo.ca

55. Overview
• What is COM / DCOM / COM+?
• COM
– Client/Server Model
– Objects & Interfaces
– COM Servers
– COM Clients
– COM Library
– COM Example
• DCOM
• COM+

56. What is COM / DCOM / COM+?
• COM (Component Object Model)
– software architecture which allows components from multiple
vendors to be combined in a variety of applications
– binary standard for component interoperability
– platform and language independent, distributed, object-oriented.
– is the foundation technology for Microsoft's OLE and ActiveX®
technologies, as well as others.
• DCOM (Distributed Component Object Model)
– enables software components to communicate directly over a
network in a reliable, secure, and efficient manner.
– is designed for use across multiple network transports.
– based on the OSF's DCE-RPC specification.

57. What is COM / DCOM / COM+?
• COM+ (Component Services)
– upgrade of the original COM
– Adds
• Transaction processing from Microsoft Transaction Manager
• Queued components
• Object pooling
• Publish-subscribe event service
• much, much, more.

58. Client/Server Model
Client
Application
COM
Server
Object
(1) “Create
Object” (2) Locate
implementation
(3) Get object
interface pointer,
return to Client
(4) Call interface
members

59. Objects & Interfaces
• Interface
– a set of member functions that a client can call to access that object
implementation.
– all interfaces start with an ‘I”, followed by a descriptive label
identifying what services they provide.
– all interfaces have a IID (interface identifier) which uniquely
identifies them.
• Object
– an implementation of one or more interfaces
– If object wishes to allow COM to locate and launch its
implementation then it needs to have a CLSID (class identifier)
– at very least, objects must implement IUnknown interface
• QueryInterface(), AddRef(), Release()

60. COM Servers
• Servers come in three varieties:
– In-process
• Server loaded into the clients process space
• loaded as a Dynamic Linked Library (DLL)
– Local
• Server that runs as a separate process on the same machine as
the client
• run as an executable (EXE) application
– Remote
• Server that runs as a separate process on another machine
• DLL or EXE

61. COM Servers
• Servers have four responsibilities
– Allocate a CLSID for each supported class and provide a mapping
between CLSID and server module (registry)
– Implement a class factory object with the IClassFactory interface
(CreateInstance & LockServer) for each CLSID
– Expose the class factory so the COM Library can find it once it is
loaded (CoRegisterClassObject or DllGetClassOjbect)
– Provide for unloading the factory if is serving no objects and no
locks are in place

62. COM Clients
• Any application which uses COM to instantiate objects
• Object usage involves:
– Using CLSID through COM Library or class factory to get an
interface pointer
• Interface pointer is actually a pointer to a pointer to a table of
function pointers
– Using interface pointer to call member functions or to obtain other
interfaces
– Calling Release() function when done with object.

63. COM Library
• COM Library provides :
– A small number of API functions that facilitate the creation of COM
applications
• clients (object creation).
• servers (object exposure).
– Implementation locator services
• COM determines, from a class identifier, which server
implements that class and where that server is located
(registry).
– Transparent remote procedure calls when an object is running in a
local or remote server

64. COM Example
class StockQuote : public IUnknown {
public:
HRESULT QueryInterface( IID & iid, void** ppvObj );
ULONG AddRef();
ULONG Release();
HRESULT getSymbol( char** symbol );
HRESULT getLongName( char** name );
HRESULT getPrice( int* price )
private:
int _price;
char* _symbol;
char* _name
};

65. COM Example
HRESULT StockQuote::QueryInterface( IID & iid, void** ppvObj ) {
HRESULT retVal = S_OK;
if( IsEqualID( iid, IID_IUnknown )
*ppvObj = ( IUnknown*) this;
else {
*ppvObj = NULL;
retVal = E_NOINTERFACE;
}
return retVal;
}

66. COM Example
hRes = CoCreateInstance(&CLSID_STOCK, NULL,
CLSCTX_SERVER,
&IID_IUnknown, &pStock);
if (SUCCEEDED(hRes)) {
// do something with pStock
}
else {
// report error
}

67. DCOM
• Extends COM to support object communication across
networks.
• DCOM protocol, Object RPC, extends DCE RPC
– Uses RPC packets with extra information such as interface pointer
identifiers
– Programmers generally write an IDL and use an IDL compiler
(MIDL) to generate proxies/stubs
• Pinging for garbage collection

68. DCOM
In-Process
Object
Client
Application
Local
Object
Proxy
Remote
Object
Proxy
In-Process Server
COM
Client Process
RPC
RPC
Local
Object
Local Server
Stub
COM
Local Server Process
Remote
Object
Remote Server
Stub
COM
Remote Server Process
Remote Machine

69. COM+
• Transactions
– Coordination between COM+ and DTC (Distributed
Transaction Coordinator) to ensure ACID properties.
• Queued Components
– Provides asynchronous component invocation and execution
through the use of Microsoft Message Queuing Service
• Object Pooling
– Automatic service provided by COM+ which allows
components to have instances of itself kept active in a pool
• Stateless
• No thread affinity
• Aggregatable

70. COM+
• COM+ Events