Objectives: 1. Understand MVC and Struts 2 Architecture

2. Analyze Page-centric and Servlet-centric Designs

3. Develop JSP Interactive Interfaces

Struts 2 Architecture and Overview

Topics

Introduction to Struts 2 Model-View-Controller Architecture Struts and MVC Architecting Web Applications Page-centric Design Servlet-centric Design JSP Interactive Interfaces FormBean

Struts Classic Project

Combines JSPs and Servlets Targets a Model-View-Controller (MVC)

Architecture Conceived by Craig McClanahan in May 2000 Support by Application Servers

BEA GlassFish JBoss Apache’s Tomcat

Struts 2

Apache Project Based on OpenSymphony WebWork framework Implements MVC Takes advantage of the lessons learned from

Struts Classic to present a cleaner implementation of MVC

New Features Interceptors Annotation-based Configuration and more…

Other Web ApplicationFrameworks

Stripes Cocoon Echo Nacho Spring MVC JBanana WebWork (now Struts 2) many others…

What is a Web Application Framework?

A web application framework is a piece of structural software that provides automation of common tasks of the domain as well as a built- in architectural solution that can be easily inherited by applications implemented on the framework.

Common Tasks of the Web Application

Binding Request Parameters to Java Types Validating Data Making calls to business logic Making calls to the data layer Rendering presentation layer (HTML, …) Providing internationalization and localization

Struts 2 Project

Keep Presentation Layer Separate from Data Layer

Model-View-Controller Architecture Model (Struts 2: action)• Represents the Data Objects

View (Struts 2: result)• Screen representation of the Model

Controller (Struts 2: FilterDispatcher)• How the user interface reacts to the user’s input

Advantages of MVC

ReliabilityHigh Reuse and AdaptabilityLow Development CostsRapid DeploymentMaintainability

MVC Architecture Goals

View

Controller

Model

Applying MVC to WebApplications

View: HTML form; native Java interface; client-side

script; applet

Controller: Java servlet; session Bean

Model: Entity Bean or other business logic object

Interchangeable Elements

View: HTML form becomes touch-screen

Controller: JSP becomes session bean

Model: Entity Bean

MVC and GUIs

Views and Controllers closely interact (HTML/JSP)

If HTML code is written out entirely through JSP, the Controller and View (conceptually) merge

A Controller-View pair works with one ModelOne Model may have multiple Controller-View

pairs

MVC Advantages

Single point of entry to Model objectMultiple-client supportDesign clarityModularityControlled growthPortable

Struts 2 and MVC

To support MVC, struts uses: JSPs Custom JSP Tags Java Servlets POJOs for Actions

Struts 2 and MVC

View FilterDispatcher(Controller)

request

Struts 2 and MVC

Controller - FilterDispatcher Front Controller pattern Maps Requests to Actions Servlet Filter that inspects each incoming

request to determine which Struts 2 action should handle the request.

Struts 2 and MVC

FilterDispatcher(Controller) Action 1

Action 2

Action 3

Action 4

ActionInvocation

Struts 2 and MVC

Action 1

Action 2

Action 3

Action 4

Models

Struts 2 and MVC

ActionInvocation

Action 1

Action 2

Action 3

Action 4

Struts 2 and MVC

ActionInvocationView

Struts 2 and MVC

The Struts 2 solution to implementing MVC View – JSP Page, Velocity, XSLT, RIA, AJAX Controller – FilterDispatcher in conjunction

with user-defined Action classes Model – Action classes is a locus of data

transfer, a single unit of work that conducts calls to the business logic

Designing Web Applications

High Level Architecture

PresentationLayer

ControlLayer

ApplicationLogic

DataSources

Architectural Approaches

Page-centric Design Model 1 Control and application Logic handled by JSP

Servlet-centric Design Model 2 Intermediate servlet ( or servlets ) manage

control and application logic

Page-Centric Design

Series of interrelated JSP pages JSP page

Perform request processing Communicate with back-end data sources Generate dynamic content elements

Page-centric Program Flow

Role-based Pages

Options.jsp Query.jsp Display.jsp

DataSources

Simple page-centric application

Password.htm

<HTML><BODY><form action="PasswordGen.jsp" method="POST"><H3>Welcome to the Password Generator</H3>First Name: <input type="text" name="firstName"><br>Last Name: <input type="text" name="lastName"><br><p><input type="submit" value="Generate Password"></form></BODY></HTML>

Simple page-centric application

Simple page-centric application

PasswordGen.jsp<html><body><% String firstName = request.getParameter("firstName"); String lastName = request. getParameter("lastName"); String password;if( (firstName.length()>=2) && (lastName.length()>=2))

password = lastName.substring(0,2)+firstName.substring(0,2); else password = "NoGo";%><h1>Password Generated!</h1>Your super secret password is <%= password %>.<br><a href="Password.htm">To generate another password.</a></body></html>

Simple page-centric application

Page-centric Strategy

Page-centric approach Benefits Very little abstraction Few components Minimum of layers

Page-centric approach Limitations Maintainability Flow Control

Servlet-centric Design

Servlet handles control and application logic Requests are routed to the JSP pages via the

servlet Servlet can perform the following:

Execution of specific business actions on behalf of a JSP

Deliver data to a JSP Control flow among JSP pages

Command Pattern

Encapsulate each command our servlet can handle into its own class

String cmd = req.getParameter(“cmd”);if (cmd.equals(“buy”)) {BuyCmd bcmd = new BuyCmd();bcmd.buy(); }

if (cmd.equals(“sell”)) {SellCmd scmd = new SellCmd();scmd.sell(); }

Servlet-centric Program Flow

Client Servlet

JSP

DataSources

Simple Servlet-centric application

Password.htm

<HTML><BODY><form action="/webapp/passwordservlet" method="POST"><H3>Welcome to the Password Generator</H3>First Name: <input type="text" name="firstName"><br>Last Name: <input type="text" name="lastName"><br><p><input type="submit" value="Generate Password"></form></BODY></HTML>

Simple Servlet-centric application passwordServlet.java

public void doPost(HttpServletRequest request,

HttpServletResponse response) throws ServletException, IOException {

GenBean gb = new GenBean(); gb.setFirstName(request.getParameter("firstName")); gb.setLastName(request.getParameter("lastName")); gb.generate(); request.setAttribute("gen", gb); RequestDispatcher rd =

getServletContext().getRequestDispatcher("/PasswordGen.jsp");

rd.forward(request, response); }

Simple Servlet-centric application

GenBean.java public class GenBean { private String firstName; private String lastName; private String password = "NoGo"; public String getFirstName(){return firstName;} public void setFirstName(String fn){ firstName = fn;} public String getLastName(){return lastName;} public void setLastName(String ln){ lastName = ln;} public String getPassword(){return password;} public String generate() { if( (firstName.length() >= 2) && (lastName.length() >= 2)) password = lastName.substring(0,2) + firstName.substring(0,2); return password; }}

Simple Servlet-centric applicationPasswordGen.jsp

<html><body><jsp:useBean id = "gen" class = “genpackage.GenBean"

scope="request"/><h1>Password Generated!</h1>Your super secret password is <jsp:getProperty

name="gen" property="password"/><br><a href="Password.htm">To generate another

password.</a></body></html>

Interactive Interfaces using JSP

Creating Web-based applications that exhibit behavior of desktop programs

Must address the stateless nature of Web pages and Form elements

Sticky WidgetsValidation

Dynamically Generated HTML

Use HTML form elements in Web applications State is encoded into the HTML typically as value

attributes or the checked keyword To maintain state

Cookies with JavaScript Dynamically generated HTML with JSP• Create a JSP that combines the form and results on

the same page• Use with Model 1 approach

Sticky Widget Example:Text Fields

Text Field state is defined in the value attribute

<input type=“text” name=“desc”value=“<%= getParam(request, “desc”) %>”>

public String getParam(HttpServletRequest req, String param) {if (req.getParameter(param) == null)

return “”;else

return req.getParameter(param);}

Sticky Widget Example:Radio Buttons

Radio Button state is defined by the checked keyword

<input type=“radio” name=“binary” value=“yes” <%= isChecked(request,“binary”,“yes”) %>>Yes<br>

<input type=“radio” name=“binary” value=“no” <%= isChecked(request,“binary”,“no”) %>>No<br>

public String isChecked(HttpServletRequest req, String param, String testValue) {return testValue.equals(req.getParameter(param)) ? “checked” : “”;

}

Validating Form Data

Client-Side Performed with JavaScript User is prohibited from submitting form until

validated Server-Side

Request data not guaranteed to come from browser

Use JSP sticky widgets to maintain state in case of input error

Performance not as good

Form Bean

More streamlined technique for communicating the state of form data within a specific request

Allows for Model 2 approach

public class FormBean {private String name;

public void setName(String nm) {name = nm; }

public String getName() { return name; }…

}

Review

Introduction to Struts Model-View-Controller Architecture Struts and MVC Architecting Web Applications Page-centric Design Servlet-centric Design JSP Interactive Interfaces FormBean