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
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. Introduction
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.

5. Construction from Components
                                                          

6. A Bean's Public Interface
Properties
Methods
Events

7. Bean’s Properties Type of Properties
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

8. Sample Account Property Balance

9. Exposing Simple Properties
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.

10. Exposing Boolean Properties
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.

11. Exposing Indexed Properties
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)

12. Account Bean with a balance Property
// 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

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
setBalance called
Account notifies the VetoableChangeListeners
of pending change request
Listeners can optionally throw exception
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. Exposing Bean Custom Events
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

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. Reflection API
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

21. Bean Distribution
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.

22. Summary 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

23. Outline (Part B) 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

24. Introduction
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 25
Running
Montreal
Nike 50
ShoeCollection id
name
branch
brand
quantities
Shoe 24

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

26. JBoss Application Server
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

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

28. Enterprise Java Beans (contd.)
JBoss Application Server
Home
EJB Container
Interface
EJB
EJB
Home Object
Home Object
Remote
Interface
Bean Class
EJB
EJB
Client
Client
Object
Object
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. Accessing a Business Method
Retrieval of the Home object reference and generation of remote EJB object reference.
5: Return EJB
object reference
3: Request new
EJB object
Client Code
EJB Container
Home Object
1: Retrieve
reference
2: Return Home
Object reference
Home Object
Home Interface
4: Create EJB object
Enterprise Bean
JNDI
EJB Object
Remote Interface
Directory Service 29

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

31. Shoe Distributed Web Application
Presentation
Layer
Business Logic
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

32. Demonstration of application lifecycle
Build
Package
Deploy
Run
shoe.jar
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
cs854-WebServer
WEB-INF
classes
header.html
JspShoeBrowse.class
search.jsp
lib
browse.jsp
web.xml
shoe.jar
mext.jsp
footer.html
prev.jsp 32

33. Summary 33

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. CORBA Architecture ORB OS Kernel OS Kernel Network Client
Object Implementation
IDL
Skeleton
Object
Adapter
Dyn.
Inter-
face
IDL
Stub
ORB
Interface
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. Client - Manage ORB in Stock Quoter
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.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
Factory_i.cpp
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 (); }

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
Stock_i.cpp
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 ()); }

44. Implement Server int main (int argc, char* argv[]) { try
Server.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! */);
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; }

45. Software Bus
CORBA provides a communication infrastructure for a heterogeneous, distributed collection of collaborating objects
Analogous to “hardware 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 /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=' & _     "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=' & _     "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

55. Overview What is COM / DCOM / COM+? COM DCOM 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.
For any given platform (hardware and operating system combination), COM defines a standard way to lay out virtual function tables (vtables) in memory, and a standard way to call functions through the vtables.

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

59. Objects & Interfaces Interface Object
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 Local Remote
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 Client Process Local Server Process Remote Machine
In-Process
Object
Local Server Process
Local
Object
Client
Application
Stub
In-Process Server
COM
RPC
Local Server
Local
Object
Proxy
COM
Remote Machine
Remote Server Process
Remote
Object
Proxy
Remote
Object
Stub
RPC
COM
Remote Server

69. COM+ Transactions Queued Components Object Pooling
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
Atomic, Consistent, Isolated, Durable

70. COM+
COM+ Events