Struts Tag Library

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Example2: FovoritesForm Class (ch 03) 1

public final class FavoritesForm extends ActionForm {

2 3 private static String[] javaIdes = new String[] {"Eclipse", "IDEA", "JBuilder", "JDeveloper", "NetBeans"}; 4 private static String[] csharpIdes = new String[] {"SharpDevelop", "Visual Studio"}; 5 6 public FavoritesForm() { 7 webLinks = new ArrayList(); 8 for (int i=0; i<5; i++) webLinks.add(new WebLink()); 9 colors = new String[3]; 10 colors[0]="Black"; 11 colors[1]="Blue"; 12 colors[2]="Red"; 13 } 14 ... 15 public String[] getColors() { 16 return colors; 17 }

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Use it to output the contents of a bean's property The information returned to the page is rendered as a String Use it to encode and unencode information

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Example1: <jsp:useBean id="dvd" class="hansen.playground.DVD" scope="request"/> ... <jsp:getProperty name="dvd" property="title"/> Using Struts you simply use the write tag:

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Example2: submitAction.java 1 public final class SubmitAction extends Action { 2 3 // The execute() method is where you provide your business logic 4 public ActionForward execute(ActionMapping mapping, 5 ActionForm form, 6 HttpServletRequest request, 7 HttpServletResponse response) { 8 9 // Cast ActionForm object to SubmitForm type 10 SubmitForm f = (SubmitForm) form; 11 12 // Retrieve the value of lastname field 13 String lastName = f.getLastName(); 14 15 // Translate the lastname to upper case and save it Request scope 16 request.setAttribute("lastName", lastName.toUpperCase()); 17 18 // Create and return ActionForward object with "success" outcome 19 return (mapping.findForward("success")); 20 } 21 }

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Example2: submit.jsp 1 2 3 4 5 6 7 8 9 10 11 12 13

Hello young old

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Example3: view_favorites.jsp (ch 03) 1

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<script language="JavaScript"> function showMessage() { alert( "Hello, !" ); }

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Looks up a key in the resource file

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Example: index.jsp (ch 03) 1



Struts Chapter 3 Examples



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Get a request parameter Example –



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HTML Tags 25

HTML Tags ●

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Form bridge between JSP view and other components Input forms are important for gathering userentered data Most of the actions of the HTML taglib involve HTML forms Error messages, hyperlinking, internationalization

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HTML Tags ● ● ● ● ● ● ● ● ● ● ●

checkboxes hidden fields password input fields radio buttons reset buttons select lists with embedded option or options items option options submit buttons text input fields textareas 27

HTML Tags ● ● ● ● ● ●



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Simplest way to display error messages –

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It is expected that ActionErrors is created (either in the validate() method of an ActionForm class or in execute() method of an Action class)

Place the tag anywhere on the page you want the list of errors to be displayed Iterates over the errors writing unescaped contents to the page –

Messages need to have HTML tags, which are not desirable 29

Example: submit.jsp 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23

<%@ page language="java" %> <%@ taglib uri="/WEB-INF/struts-bean.tld" prefix="bean" %> <%@ taglib uri="/WEB-INF/struts-html.tld" prefix="html" %> <%@ taglib uri="/WEB-INF/struts-logic.tld" prefix="logic" %>

Example Submit Page

Last Name:
Address:
Sex: Male Female
Married:
Age: 0-19 20-49 50-

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Example: ApplicationResources.properties 1 errors.header=

Validation Error(s)

2 3 error.lastName=
• Enter your last name 4 error.address=
• Enter your address 5 error.sex=
• Enter your sex 6 error.age=
• Enter your age 7 error.birthYear=
• Enter the year you were born between 1900 and 2004 inclusive 8 9 errors.footer=

---



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Corrects the problem of –

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Allows you to keep HTML tags in JSP pages not in the resource file

By default, it looks for error messages stored in the request scope The id attribute defines the name of the scripting variable used to expose the error message text

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Logic Tags 33

Logic Tags ●

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Provides presentation logic tags that eliminate need for scriptlets Value comparisons Include: = != <= >= < >

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Substring matching –

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Presentation logic –

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match, notmatch forward, redirect

Collections –

iterate

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Logic Tags ● ●



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& tags ●

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The body of the tag is evaluated whenever the JavaBean, or its property, is present within the JSP page Attributes for evaluation – – – – –

name parameter cookie header property 36

Example: submit.jsp 1 2 Hello 3 4 young 5 6 7 old 8 9 10 11 12 13

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& tags ● ●

Checks against a specific value in a bean Assumes the bean exists –

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Exception occurs if not

tag compares the bean's toString() value aganst the value property If property attribute is specified, then the value attribute is compared against the bean's property 38

Example: submit.jsp 1 2 Hello 3 4 young 5 6 7 old 8 9 10 11 12 13

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Usage Example: & tags ●

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You want to present different messages or buttons on a page depending upon the type of action you migt perform Example: –

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Depending what a user wants to do (mode) – view, edit, or delete, you want to present different set of buttons View mode: Show only view button Edit mode: Show view and edit buttons Delete mode: Show only delete button 40

Example: subscription.jsp (ch 13) 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15

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Template Tags 42

Template Tags ●

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Templates are JSP pages that include parameterized content Useful for creating dynamic JSP templates for pages that share a common format Functionality provided is similar to what can be achieved using the standard JSP include directive, but these tags allow for dynamic rather than static content

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Template Tags ●

Three template tags work in an interrelated function: –

Get - Gets the content from request scope that was put there by a put tag.

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Insert - Includes a template

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Put - Puts content into request scope

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Template sample (insert/put)



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layout.jsp

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Struts and JSTL 47

When to JSTL in your Struts application? ●

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Developers should evaluate when to use the JSTL Many of the Struts taglib features are now available in the JSTL It’s simple: If the tag exists in the JSTL – use it Continue using the Struts tags where appropriate, they will continue to be supported 48

Interaction with JSTL ●

Struts-el taglibs allow for using expression values instead of just rtexprvalue Runtime: Expression:

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Set of optional taglibs that can be used with the JSTL expression language (EL) Implements many (but not all) of the Struts tags. Located in the contrib folder of the Struts release Container with servlet 2.3 support required

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Struts EL Tag library 50

Struts EL Extension ● ●

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Extension of the Struts tag library Uses the expression evaluation engine in the Jakarta Taglibs implementation of the JSP Standard Tag Library (version 1.0) to evaluate attribute values Some of the Struts tags were not ported to this library –

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their functionality was entirely supplied by the JSTL

Requires the use of the Struts tag library, and the Java Server Pages Standard Tag Library 51

Tag Mapping ●

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Every Struts tag that provides a feature that is not covered by the JSTL (1.0) library is mapped into the Struts-EL library Bean Tag Library Tags NOT Implemented in Struts-EL – –

cookie (in Struts): c:set, EL (in JSTL) define (in Struts), c:set, EL (In JSTL)

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How to use Struts EL ●

Struts –

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Struts EL –



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Best Practice Guidelines 54

Follow Good MVC Practice ●

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JSP pages must “know” as little as possible about the back-end architecture JSP page should only concern itself with rendering the view and not manipulating any data logic

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Passion!

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