CS 160: Software Engineering September 10 Class Meeting Department of Computer Science San Jose State University Fall 2014 Instructor: Ron Mak mak.

CS 160: Software EngineeringSeptember 10 Class Meeting

Department of Computer ScienceSan Jose State University

Fall 2014Instructor: Ron Mak

www.cs.sjsu.edu/~mak

http://www.cs.sjsu.edu/~mak

http://www.cs.sjsu.edu/~mak

Computer Science Dept.Fall 2014: September 10

CS 160: Software Engineering© R. Mak

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Model-View-Controller Architecture (MVC)

The Model-View-Controller (MVC) architecture is used for client-server applications that include a user interface._



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Three Types of MVC Objects

Model objects Maintain the data and knowledge

of your application.

View objects Display the model to the user. The presentation layer.

Controller objects Manage the application flow. Handle user interactions.



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Model-View-Controller Operation The user interacts with the

controller to send it commands. Via buttons, text fields,

mouse actions, etc.

The commands may tell the controller to modify the view directly, or the controller may alter the state of the model.

The altered model causes the view to update how it displays the model’s data.

The user may react to changes in the view by interacting with the controller to send new commands.

The user never manipulates the model directly,

only through the controller.



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Model-View-Controller Example

alter state

update update

CONTROLLER

MODEL

VIEW #1 VIEW #2

User

send command



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MVC Implementation for Web Applications

Implement the controller with servlets.

Goal: Reduce the amount of Java code in the JSPs. Move control logic into servlets. Servlets are multi-threaded and can be shared.

Implement the view with JSPs.

view = web pages JSPs should look like HTML as much as possible. Include tags for dynamically generated data.

_



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MVC Implementation, cont’d

Implement the model with JavaBeans.

Persist the data maintained by the JavaBeans into a backend data repository, such as a MySQL database._



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MVC Implementation: Loose Coupling

Keep the implementations of the three objects types separate.

Each type of objects does not depend on how the other types are implemented.

Your application is more robust (resilient to change)._



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MVC Implementation: Parallel Development

Controller (servlets) Java programmers

View (JSPs) Web page designers

Model (JavaBeans and database) Java programmers Database developers

_



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Handle User Interactions with Servlets Forms on HTML pages should send user data to servlets.

<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN"><html><head> <title>Murach's Java Servlets and JSP</title></head><body> <h1>Join our email list</h1> <p>To join our email list, enter your name and email address below. <br> Then, click on the Submit button.</p> <form action="addToEmailList" method="get"> <table cellspacing="5" border="0"> ... </table> </form></body></html>

Servlet



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Handle User Interactions with Servlets, cont’d Map a servlet name in the application file WEB-INF/web.xml

<?xml version="1.0" encoding="UTF-8"?><web-app version="2.5" xmlns="http://java.sun.com/xml/ns/javaee" ...>

...  <servlet> <servlet-name>AddToEmailListServlet</servlet-name> <servlet-class>music.email.AddToEmailListServlet</servlet-class> </servlet>

...

 <servlet-mapping> <servlet-name>AddToEmailListServlet</servlet-name> <url-pattern>/addToEmailList</url-pattern> </servlet-mapping>

...</web-app>

NetBeans will automaticallycreate this mapping for you.



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Servlet Servlet JSP

After a servlet has done its work (possibly including interactions with the model components), it may want to pass data

to another servlet for more work, or

to a JSP to display the next web page.

Servlets are shared, multi-threaded code!



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Servlet Servlet JSP, cont’d

The originating servlet stores the data into the request object:

User user = new User(firstName, lastName, emailAddress);request.setAttribute("userObj", user);



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The servlet forwards the request to a target servlet or JSP:

String url = "/cart/displayUserInfo.jsp";RequestDispatcher dispatcher = getServerContext().getRequestDispatcher(url);dispatcher.forward(request, response);



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The target servlet or JSP retrieves the data from the request object:

User user = (User) request.getAttribute("userObj");



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Analysis

Identifying the three types of objects of a MVC application architecture is part of analysis._



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Analysis Goal

Build an analysis model of the application that you’re developing that is correct, complete, consistent, and unambiguous.

Model building is a highly iterative and incremental activity.

The model describes the application domain.

Developers work with clients to update the functional specification as they discover new requirements.

Don’t confuse the uses of the word modelin Model-View-Controller and analysis model.



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Analysis Model Submodels

1. Functional model Use cases and scenarios UML use case diagrams and descriptions

2. Object model Derive objects from the use cases Precursor for system design UML class and object diagrams

3. Dynamic model Behavior of the system UML sequence diagrams and statecharts



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MVC Model Objects

Represent persistent information maintained by your application. AKA entity objects

Examine the participating objects in your use case descriptions.

Map parts of speech (nouns, ‘doing’ verbs, ‘having’ verbs, ‘being’ verbs, adjectives, etc.) to model components (classes, objects, operations, attributes, relationships, etc.)_



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MVC Model Objects, cont’d

Color, size, positionAttributeAdjective

Must be, shall beConstraintsModal verb

Has a, consists of, includesAggregation‘Having’ verb

Is a kind of, is one of eitherInheritance‘Being’ verb

Creates, submits, selectsOperation‘Doing’ verb

PolicemanClassCommon noun

AliceObjectProper noun

ExampleModel ComponentPart of Speech



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MVC View Objects

System interface with the actors.

View objects represent user interface components. Continue to use user-level terms.

In each use case, each actor interacts with at least one view object.

A view object collects information from the actor in a form that the model and controller objects can use._



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MVC Controller Objects

Coordinate the model and view objects.

Often have no physical counterpart in the real world. Closely related to a use case. Collect information from view objects

for dispatch to model objects. This is how user-entered data can update the model

Represent application control flows._



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Example: Bank ATM System

Log incustomer

Display balance

Shut downATM

Start upATM

Log outcustomer

Withdrawcash

Operator

Customer

Bank



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Example: Bank ATM System (cont’d) Model objects

operator customer bank account cash

View objects display options (withdraw cash,

deposit check, etc.) messages

Controller objects Start up controller (“Start up ATM” use case) User verification controller (“Log in customer” use case) Withdrawal controller (“Withdraw cash” use case)

Log incustomer

Display balance

Shut downATM

Start upATM

Log outcustomer

Withdrawcash

Operator

Customer

Bank



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Example Dynamic Model: ATM Cash Withdrawal

Customer

“Withdraw cash” Keypad Bank AccountDisplay

selectnotify

display confirmation

enter amount

notifyverify

acceptnotify

display bank adsnotify

dispense cash

TIME

UML Sequence Diagram



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Dynamic Model: UML Sequence Diagram

A UML sequence diagram represents how the behavior of a use case is distributed among the participating objects._



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Dynamic Model: UML Sequence Diagram, cont’d

Columns of the diagram represent the objects.

Horizontal arrows from one column to another represent messages or stimuli sent from one object to another (method invocations).

Receiving a message by an object triggers the object to activate an operation.

Vertical rectangles represent the duration of an operation’s activation.

Time proceeds from top to bottom.



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Dynamic Model: UML Statechart Diagram

A UML statechart diagram represents the behavior of the system from the perspective of a single object._



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Dynamic Model: UML Statechart Diagram, cont’d

Developers and clients may identify new behaviors (and new requirements).

Create statechart diagrams only for objects with extended lifetimes and state-dependent behavior

always for controller objects sometimes for model objects almost never for view objects

_



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Example: Customer Withdraws Cash from ATM

Logged in

Cardaccepted

Readingbank ads

Has cash

swipe bank card

enter PIN

enter withdrawal amount get cash

leave

UML Statechart Diagram



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Object Model Associations

An association is a relationship between two or more classes._



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Object Model Associations, cont’d

Draw a line between two classes in a UML class diagram to show a relationship.

Clarify the object model by making relationships explicit.

Discover constraints associated with relationships. An association can have a name. You can show roles and multiplicities at each end.

Do not overdo showing associations.

Teammember

Usecase

writes

author artifact

1 *



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Aggregations and Compositions

An aggregation is an “ownership” or “has a” association. Although there is a strong association between the

object and its owner, the object can exist on its own. An object can change owners or have several owners.

A composition is a “made up of” association. The constituent objects generally would not exist alone. This is the strongest association.

PageBook

aggregation

composition

Student

Shelf



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Generalization

Generalization is a special association that consolidates common attributes or behavior among classes.

Subclasses inherit attributes and behavior from their superclasses.

Person

Instructor Student

subclasses

superclass



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Attributes

An attribute is a property of an object. An association with another object is not an attribute.

Attributes are the least stable part of an object model.

Attributes often change or are discovered late. At the beginning, it’s not necessary

for attributes to describe fine details.

Student

gender : {male, female}id : Stringyear : integer

Methods will go here

Attributes

Class name



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System Design

System design is the transformation of your analysis model into a system design model.

This is the design of your entire web application._



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System Design Goal

A model that includes a subsystem decomposition and descriptions of chosen development strategies:

hardware/software strategy persistent data management strategy global control flow access control policy boundary conditions handling

_

CS 160: Software Engineering September 10 Class Meeting Department of Computer Science San Jose State University Fall 2014 Instructor: Ron Mak mak.

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