CS 772: Global Knowledge
Networks
V. “Juggy” Jagannathan
CSEE, West Virginia
University
Feb 4, 2002
Evaluating Candidate
Technologies for Boundary
Classes
Chapter 7
Based on the book: “Enterprise Java with UML”
OMG Press, John Wiley and Sons, 2001.
Technology template
Name and description: what is this technology
Details: How does it work
Strengths: What works best
Weaknesses: It’s failings
Compatible technologies
Cost of adoption: expertise, product costs
Suitability
Evaluating Swing
Sun’s GUI Platform
Swing
SUN’s GUI development framework
Runs on all platform that JVM runs
Clear separation of model/view
Mature and stable now…
Gory Details
Separation of Model and View
– E.g. DefaultTreeModel – methods to add nodes to
tree, traverse tree, remove nodes etc.
– Pg 156: ComboBoxModel Implementation
Gory Details
Event Model
– Problematic event notification e.g. Pg 157 (figure
7.2)
– Implementation of observer model. Pg 158 (figure
7.3)
– Object interactions for the Observer pattern pg 159,
figure 7.4
Gory Details
Combining User Interface Components
– Composite Pattern – pg 159, Figure 7.5
Layout managers – pg 161, figure 7.6
Putting it together – pg 162, figure 7.7
– Every association is to an interface or base class
Sample GUI program
Pg 164, 164
Strengths
– Flexibility
– Cross platform support
– Separation of model from view
Weaknesses
– Not a low-end solution – complex
– Takes time to be proficient with Swing
Other factors
Compatible Technologies
– Integrates well with server-side Java technologies –
RMI, JDBC, EJB
Cost of adoption
– Need: UI Designer, Architect, Developer
Suitability
User interface complexity
– Swing supports the entire level of UI complexity
from simple data input to dynamic views of data to
interactive graphics
Deployment Constraints – Swing does not
work with handheld devices and any web
browser. Works with late model browsers –
thru swing applets.
Other factors
Number and type of users
– Appropriate for small # of users
– May be ok for general use within an organization or for large
audience if the complexity of the interface warrants it – costs
associated with install and support.
– Not appropriate for a huge audience with low interest.
Available bandwidth
– Suitable for all bandwidth scenarios
Evaluating Java Servlets
Sun’s web platform
Java Servlets
HyperText Transfer Protocol (HTTP)
– Communication protocol between web servers and web
browsers
– Connectionless protocol
HTTP request
– Name of the requested page, info about the browser,
acceptable data types for the response, relevant cookies, and
data entered by the user
HTTP response
– Formatted data sent by the web server, expiration date for the
response, info about the server
Java Servlets
Form data – list of name-value strings collected from
the user in a form sent to the server in a HTTP request.
Cookie – information about a particular site that the
server sends and is stored on the client machine.
HTTP servlet – a Java class that accepts an HTTP
request and generates appropriate response. Servlets
extend: javax.servlet.http.HTTPServlet
Servlet engine – Allows a web server to redirect
incoming requests to a deployed servlet.
Gory Details
– Retrieving Form data
The servlet engine creates a “HttpServletRequest” object that
encapsulates the raw request and adds the form data to it. The
doPost and doGet can access form data by using:
getParameterNames and getParameter methods of
HttpServletRequest
– Sessions
Tracked using cookies. Pg 171
– HTML production
Producing clean and reusable HTML pages is a very difficult
endeavor.
Need to create a collection of reusable set of HTML production
classes.
– Concurrent Access
Evaluation
Strengths – easy to learn.
Weaknesses – easy to write spaghetti code
and difficult to maintain and extend.
Compatible technologies – HTML, DHTML,
XML and JDBC, RMI, EJB.
Cost of adoption
– Need UI Designer, Architect, Servlet Developer
Suitability
– UI Complexity
Simple data input and static views of data – easy
Customizable views – difficult – need to use javascripts
Dynamic views – more difficult – can use kludges such as
reloading data periodically using javascripts.
Interactive graphics – not possible without resorting to other plug-
ins
– Deployment constraints – can support all environments.
– Number and type of users – appropriate for all user
communities.
– Available bandwidth – generally can work with all bandwidth
options with some caveats
XML
XML Basics
Element
Document Type Definition
Parser
Authoring tool
Gory Details
Self-describing documents
Parsers
– Validating or non-validating
– Simple API for XML (SAX)
– Document Object Model (DOM)
Other aspects
Strengths
– Greatly improves data interchange between peer systems and
between people and systems
– Well worth the hype
Weaknesses
– Verbose
– Good for tree structure and not so for other relationships
Compatible technologies
– Can be used by any Java application. Can be used to store
data in the client or server. Can be used to communicate
within the same system or with external systems.
Cost of adoption
DTD author
Document author
Developer
Suitability
Data transfer
Services through a protocol
Direct access to system services
Technology selection for the time
card system
Timecard application
User interface complexity: Simple data input and static
view of data
Deployment constraints: Late-model web browser on
the internet
Number and type of users: General use within an
organization
Available bandwidth: Dial-up internet connection
Types of system interfaces: Data transfer
Performance and scalability: Concurrent updates
Technology Selection
For GUI
– Could be implemented by Swing or Servlets. There
is no additional advantage of using Swing. The
choice is for Servlets.
For system interface
– XML
The next step
UML provides package dependency diagrams.
Pg 182 Figure 7.9
Evaluating Candidate
Technologies for Control and
Entity Classes
Chapter 8
Based on the book: “Enterprise Java with UML”
OMG Press, John Wiley and Sons, 2001.
Evaluating RMI
RMI basics
Client objects communicate with server objects
Stubs and skeletons
Pg 184 figure 8.1
Gory details
Classes and interfaces
– Pg 185, figure 8.2
Remote object registration
– E.g. code pg 186
Parameter passing
– Three types: primitive data, serializable objects,
remote references
Thread safety
Development and deployment
Write remote interfaces and implementation for the
server
Use rmic command to generate stub classes
Write client applications
Distribute stub classes and any common domain
classes to the client
Start the RMI registry
Run the main application to register the remote objects
with the registry
Start the clients
Common uses of RMI
Remote object that hides entity objects (Strict layering)
– Pg 189, figure 8.3
– As long as the interface remains the same, the underlying
entity objects can be changed without impacting the clients
Direct access to entity objects (relaxed layering)
– Pg 190, figure 8.4
Direct access with event notification
– Pg 191, figure 8.5
Other factors
Strengths – great starting point for developing
distributed applications.
Weakness – leaves scalability, fault tolerance,
load balancing, data integrity to developers
Compatible technologies – servlets,
applications, applets
Cost of adoption – Architect, RMI developer
Evaluating JDBC
JDBC gory details
Java DataBase Connectivity (JDBC)
Drivers, Connections, and Statements
– Pg 195, figure 8.6 => sample sequence diagram on
the use of drivers
– Pg 196, figure 8.7 => JDBC classes
New and improved result sets
– Pg 197, figure 8.8
Other factors
Strengths – good starting point for writing
database independent code
Weaknesses – large datasets and more
complex transactions require caching,
transaction management, and connection
pooling.
Compatible technologies – any java code.
Cost of adoption – Architect, JDBC developer
Suitability of RMI and JDBC
Evaluation parameters:
– Number and type of users
– Performance and scalability
RMI and JDBC is good for all user categories
except for large to huge audiences. Does not
support load balancing.
Good for read-only systems with isolated
updates – not good for concurrent updates
EJB 1.1 evaluation
EJB Basics
– Entity bean entity objects in analysis model
– Home interface lifecycle objects in analysis model
– Session bean control objects in analysis model
– Remote interface
– Implementation
– Deployment descriptor
– Bean-managed persistence
– Container-managed persistence
– Transaction boundaries
– Container
– Persistence
Gory Details
Classes and interfaces
– Must provide a remote interface, home interface and
an implementation class
– Remote interface extends EJBObject interface
– Home interface extends EJBHome interface
– Each implementation must realize EntityBean
interface
– Figure 8.9, pg 203
Session beans
Stateful and stateless
Stateful
– Need to manage state
– Memory management trickier
– Container needs to garbage collect
Stateless
– Efficient
– Can be managed by a pool of session beans
Development Workflow
Container managed persistence
– Allocation of business data, business logic, and
control logic to entity and session beans
– Mapping entity data to persistent data store
– Determining transaction boundaries and security
Strengths & Weaknesses
Strengths
– Object lifecycle management
– Transaction management
– Security
– Persistence
– Vendor neutrality
– Portability and reuse
Weakness
– Complexity
– Price tag
Other factors
Compatible technologies
Cost of adoption
– Architect, Bean Developer, Deployer
Suitability
– Number and type of users
– Performance and scalability
Technology selection for Timecard
application
Number and type of users: general use
Performance and scalability: concurrent
updates
Conclusion: EJB has a slight edge over
RMI/JDBC solution.