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Strut FrameworkBasics

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Agenda

Introduction of MVC pattern Evolution of Web Application design

architectureModel 1Model 2Application frameworks

Apache Struts

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MVC Pattern

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Three Logical Layers in a WebApplication: Model Model (Business process layer)

Models the data and behavior behind the business process

Responsible for actually doing Performing DB queries Calculating the business process Processing orders

Encapsulate of data and behavior which are independent of presentation

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Three Logical Layers in a WebApplication: View View (Presentation layer)Display information according to client

typesDisplay result of business logic (Model)Not concerned with how the information

was obtained, or from where (since that is the responsibility of Model)

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Three Logical Layers in a WebApplication: Controller Controller (Control layer)

Serves as the logical connection between the user's interaction and the business services on the back

Responsible for making decisions among multiple presentations e.g. User's language, locale or access level dictates a

different presentation. A request enters the application through the control

layer it will decide how the request should be handled and what information should be returned

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Evolution of MVC Architecture

No MVC MVC Model 1 (Page-centric) MVC Model 2 (Servlet-centric) Web application frameworks

Struts Standard-based Web application framework

JavaServer Faces (JSR-127)

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Model 1 Architecture (Page-centric)

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Page-centric Architecture

Composed of a series of interrelated JSP pages JSP pages handle all aspects of the application

presentation, control, and business process

Business process logic and control decisions are hard coded inside JSP pages in the form of JavaBeans, scriptlets, expression

Next page selection is determined by A user clicking on a hyper link, e.g. <A HERF="find.jsp> Through the action of submitting a form, e.g. <FORM ACTION="search.jsp">

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Page-centric Architecture

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Page-centric Scenario

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Model 2 Architecture (Servlet-centric)

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Why Model 2 Architecture?

What if you want to present different JSP pages depending on the data you receive? JSP technology alone even with JavaBeans and

custom tags (Model 1) cannot handle it well Solution

Use Servlet and JSP together (Model 2) Servlet handles initial request, partially process the

data, set up beans, then forward the results to one of a number of different JSP pages

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Servlet-centric Architecture

JSP pages are used only for presentation Control and application logic handled by a servlet (or set of

servlets) Servlet serves as a gatekeeper

Provides common services, such as authentication, authorization, login, error handling, and etc

Servlet serves as a central controller Act as a state machine or an event dispatcher to decide upon the

appropriate logic to handle the request Performs redirecting

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Servlet-centric Scenario

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Web Application Frameworks

Based on MVC Model 2 architecture Web-tier applications share common set of

functionalityDispatching HTTP requests Invoking model methodsSelecting and assembling views

Provide classes and interfaces that can be used/extended by developers

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Why Web Application Framework?

Built-in de-coupling of presentation tier and business logic into separate components

Provides a central point of control Provides rich set of features Facilitates unit-testing and maintenance Availability of compatible tools Provides stability Enjoys community-supports Simplifies internationalization Simplifies input validation

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Why Web Application Framework?

Frameworks have evolved with Java Server technologyJSP/Servlets are still hard to use

Frameworks define re-usable components to make this job easier.

A good framework defines how components work to create a usable application.

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Web Application Frameworks

Apache Struts JavaServer Faces (JSR-127)A server side user interface component

framework for JavaTM technology-based web applications

Echo Tapestry

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Apache Struts

Struts is an open source Web application framework developed as Apache Jakarta project http://jakarta.apache.org/struts/

Model-View-Controller (MVC) framework Used for constructing web applications based

Servlets and JSP technologies Struts application is a genuine Web application that

should be able to run on any Sevlet container including all JavaEE compliant App servers

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How Struts Works

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The controller components

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Sample Application Things to doCreating ActionForm object

Input validationCreating Action object

Forwarding at either success or failure through configuration set in struts-config.xml file

You can also build it using NetBeans

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Step by Step1. Create development directory structure2. Write web.xml3. Write struts-config.xml4. Write ActionForm classes5. Write Action classes6. Create ApplicationResource.properties7. Write JSP pages8. Build, deploy, and test the application

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Step 1: Create DevelopmentDirectory Structure Same development directory structure for

any typical Web application Ant build script should be written

accordingly If you are using NetBeans, the

development directory structure is automatically created

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Step 2: Write web.xmlDeployment Descriptor Same structure as any other Web application

ActionServlet is like any other servlet Servlet definition and mapping of ActionServlet

needs to be specified in the web.xml There are several Struts specific

<init-param> elements Location of Struts configuration file

Struts tag libraries could be defined

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Example: web.xml1.<?xml version="1.0" encoding="UTF-8"?>2.<web-app version="2.4" xmlns="http://java.sun.com/xml/ns/j2ee"xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"xsi:schemaLocation="http://java.sun.com/xml/ns/j2eehttp://java.sun.com/xml/ns/j2ee/web-app_2_4.xsd">3. <servlet>4. <servlet-name>action</servlet-name>5. <servlet-class>org.apache.struts.action.ActionServlet</servlet-class>6. <init-param>7. <param-name>config</param-name>8. <param-value>/WEB-INF/struts-config.xml</param-value>9. </init-param>10. ...11. </servlet>12. <servlet-mapping>13. <servlet-name>action</servlet-name>14. <url-pattern>*.do</url-pattern>15. </servlet-mapping>

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Step 3: Writestruts-config.xml Identify required input forms and then define

them as <form-bean> elements Identify required Action's and then define them

as <action> elements within <action-mappings>elementmake sure same value of name attribute of <form-

bean> is used as the value of name attribute of <action> element

define if you want input validation Decide view selection logic and specify them as

<forward> element within <action> element

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struts-config.xml: <form-beans>1.<?xml version="1.0" encoding="UTF-8" ?>2.<!DOCTYPE struts-config PUBLIC3."-//Apache Software Foundation//DTD Struts Configuration

1.2//EN"4."http://jakarta.apache.org/struts/dtds/struts-

config_1_2.dtd">

5.<struts-config>6. <form-beans>7. <form-bean name="submitForm"8. type="submit.SubmitForm"/>9. </form-beans>

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struts-config.xml: <action mappings>

10. <!-- ==== Action Mapping Definitions ==============-->11. <action-mappings>12. <action path="/submit"13. type="submit.SubmitAction"14. name="submitForm"15. input="/submit.jsp"16. scope="request"17. validate="true">18. <forward name="success" path="/submit.jsp"/>19. <forward name="failure" path="/submit.jsp"/>20. </action>21. </action-mappings>s

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Step 4: Write ActionForm classes Extend org.apache.struts.action.ActionForm

class Decide set of properties that reflect the input

form Write getter and setter methods for each

property Write validate() method if input validation is

desired

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Write ActionForm class1.package submit;2.import javax.servlet.http.HttpServletRequest;3.import org.apache.struts.action.*;4.public final class SubmitForm extends ActionForm {5. /* Last Name */6. private String lastName = "Hansen"; // default value7. public String getLastName() {8. return (this.lastName);9. }10. public void setLastName(String lastName) {11. this.lastName = lastName;12. }13. /* Address */14. private String address = null;15. public String getAddress() {16. return (this.address);17. }18. public void setAddress(String address) {19. this.address = address;20. }21....

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Write validate() method22. public ActionErrors validate(ActionMapping mapping,23. HttpServletRequest request) {24. // Check for mandatory data25. ActionErrors errors = new ActionErrors();26. if (lastName == null || lastName.equals("")) {27. errors.add("Last Name", new 28. ActionError("error.lastName"));29. }30. if (address == null || address.equals("")) {31. errors.add("Address", new ActionError("error.address"));32. }33. if (sex == null || sex.equals("")) {34. errors.add("Sex", new ActionError("error.sex"));35. }36. if (age == null || age.equals("")) {37. errors.add("Age", new ActionError("error.age"));38. }39. return errors;40. }41. ...

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Step 5: Write Action classes

Extend org.apache.struts.action.Actionclass

Handle the requestDecide what kind of server-side Model objects

(EJB, JDO, etc.) can be invoked

Based on the outcome, select the next view

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Example: Action Class1.package submit;2.import javax.servlet.http.*;3.import org.apache.struts.action.*;4.public final class SubmitAction extends Action {5. public ActionForward execute(ActionMapping mapping,6. ActionForm form,7. HttpServletRequest request,8. HttpServletResponse response) {9. SubmitForm f = (SubmitForm) form; // get the form bean10. // and take the last name value11. String lastName = f.getLastName();12. // Translate the name to upper case13. //and save it in the request object14. request.setAttribute("lastName", lastName.toUpperCase());15.16. // Forward control to the specified success target17. return (mapping.findForward("success"));18. }19.}

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Step 6: CreateApplicationResource.properties and Configure web.xml accordingly

1.errors.header=<h4>Validation Error(s)</h4><ul>2.errors.footer=</ul><hr>3.error.lastName=<li>Enter your last name4.error.address=<li>Enter your address5.error.sex=<li>Enter your sex6.error.age=<li>Enter your age

Example: ApplicationResource.properties

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Step 7: Write JSP pages

Write one JSP page for each view Use Struts tags forHanding HTML input formsWriting out messages

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Example:submit.jsp1. <%@ page language="java" %>2. <%@ taglib uri="/WEB-INF/struts-bean.tld" prefix="bean" %>3. <%@ taglib uri="/WEB-INF/struts-html.tld" prefix="html" %>4. <%@ taglib uri="/WEB-INF/struts-logic.tld" prefix="logic" %>5. <html>6. <head><title>Submit example</title></head>7. <body>8. <h3>Example Submit Page</h3>9. <html:errors/>10. <html:form action="submit.do">11. Last Name: <html:text property="lastName"/><br>12. Address: <html:textarea property="address"/><br>13. Sex: <html:radio property="sex" value="M"/>Male14. <html:radio property="sex" value="F"/>Female<br>15. Married: <html:checkbox property="married"/><br>16. Age: <html:select property="age">17. <html:option value="a">0-19</html:option>18. <html:option value="b">20-49</html:option>19. <html:option value="c">50-</html:option>20. </html:select><br>21. <html:submit/>22.</html:form>

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Example: submit.jsp (cont.)...

23. <logic:present name="lastName" scope="request">24. Hello25. <logic:equal name="submitForm" property="age" value="a">26. young27. </logic:equal>28. <logic:equal name="submitForm" property="age" value="c">29. old30. </logic:equal>31. <bean:write name="lastName" scope="request"/>32.</logic:present>33.</body>34.</html>

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Step 8: Build, Deploy,and Test Application

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Accessing Web Application

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Acknowledgement

Most contents are borrowed from thepresentation slides of Sang Shin, Java™Technology Evangelist, Sun Microsystems,Inc.