Web component Development and JSP technologies session 13

Ver. 1.0 Slide 1 of 25

Web Component Development With Servlet and JSP™ TechnologiesObjectives

In this session, you will learn to:Describe the Java EE job roles involved in web application developmentDesign a web application using custom tagsUse JSTL tags in a JSP page


Web Component Development With Servlet and JSP™ Technologies

The following roles are involved in web application development:

Web designers:Are responsible for creating the views of the application, which are primarily composed of HTML pages.

Web component developers:Are responsible for creating the control elements of the application, which are mostly Java technology code.

Business component developers:Are responsible for creating the model elements of the application, which might reside on the web server or on a remote server.

The Java EE Job Roles Involved in Web Application Development



A custom tag is an XML tag used in a JSP page to represent some dynamic action or the generation of content within the page during runtime.Custom tags are used to eliminate scripting elements in a JSP page.JSTL tags provides the following advantages:

Java technology code is removed from the JSP pageCustom tags are reusable componentsStandard job roles are supported

Designing JSP Pages With Custom Tag Libraries



A custom tag library is a collection of custom tag handlers and the tag library descriptor file. A custom tag library is a web component that is part of the web application.Custom tag handlers uses the pageContext object to:

Access page, request, session, and application attribute scopes.Access all implicit objects in the JSP page.

Custom Tag Library Overview



All the custom tags must follow the following XML rules:Standard tag syntax must conform to the following structure:<prefix:name { attribute={”value”|’value’}}*>body</prefix:name>

For example:<c:forEach var=”message” items=”${errorMsgs}”><li>${message}</li></c:forEach>

Empty tag syntax must conform to the following structure:<prefix:name { attribute={”value”|’value’}}* />

For example:<c:url value=”addLeague.do” />

Custom Tag Syntax Rules



Tag names, attributes, and prefixes are case sensitive.For example:<c:forEach> is different from <c:ForEach><c:forEach> is different from <C:forEach><c:forEach items=”collection”> is different from <c:forEach ITEMS=”collection”>

Tags must follow nesting rules, as shown in the following structure:<tag1> <tag2> </tag2></tag1>

Custom Tag Syntax Rules (Contd.)



The following code is an example of correct nesting:<c:if test=”${not empty errorMsgs}”><c:forEach var=”message” items=”${errorMsgs}”><%-- JSP code showing a single error message--%></c:forEach></c:if>

Custom Tag Syntax Rules (Contd.)



The JSTL core library contains the following tags that reduce the scripting in a JSP page:

seturlout

JSTL Sample Tags



JSTL set Tag:The set tag is used to store a variable in a named scope, or update the property of a JavaBeans instance or Map.The two ways of using the set tag to store a variable are:

<c:set var=”varName” value=”value” [scope=”{page|request|session|application}”]/> </c:set>

<c:set var=”varName” [scope=”{page|request|session|application}”]> value in body </c:set>

JSTL Sample Tags (Contd.)



The following code demonstrates how the set tag is used to create the variable pageTitle, which is later used in an EL expression to specify the title of the JSP page:<%-- Set page title --%><c:set var=”pageTitle”>Duke’s Soccer League: Registration</c:set><%-- Generate the HTML response --%><html><head><title>${pageTitle}</title></head>




The two ways to use the set tag to modify the property of a JavaBeans instance or Map are:

<c:set target=”targetName” property=”propertyName”

value=”value” /> </c:set>

<c:set target=”targetName” property=”propertyName”>

value in body </c:set>




JSTL url Tag:The url tag is used to provide a URL with appropriate rewriting for session management. The syntax of the url tag is:<c:url value=”value” [var=”varName”] [scope=”{page|request|session|application}”] />

The following code demonstrates how the url tag can be used in a JSP page to perform URL-rewriting:<%-- Present the form --%> <form action=’<c:url value=”enter_player.do”/>’ method=’POST’>




JSTL out Tag:The out tag is used to evaluate an expression and write the result to the current JspWriter.The two forms of the out tag are:

<c:out value=”value” [escapeXml=”{true|false}”] [default=”defaultValue”] /> </c:out>

<c:out value=”value” [escapeXml=”{true|false}”]> default value </c:out>

For example, you can use the following code to display the request parameter, email, or the string, no email provided, if the parameter does not exist:

<c:out value=”${param.email}” default=”no email provided” />




The custom tag library is made up of the following two parts: The JAR file of tag handler classes The Tag Library Descriptor (TLD)

The TLD is an XML file that names and declares the structure of each custom tag in the library.A JSP page can use a tag library by directing the JSP technology translator to access the TLD. This is specified using the JSP technology taglib directive.This directive includes the TLD URI and a custom tag prefix.

Using a Custom Tag Library in JSP Pages



A JSP page may include several tag libraries. The prefix is used to distinguish custom tags from each of these libraries. The prefix is prepended to every custom tag name. Every custom tag from a given library which is used in the JSP page must use the prefix assigned to that library.The TLD file is usually stored in the WEB-INF directory.The JAR file is stored in the WEB-INF/lib directory. The symbolic name can also be specified within the tag library’s JAR file.

Using a Custom Tag Library in JSP Pages (Contd.)



The following table lists the five functional categories of tags in JSTL, their URI values, and the typical prefix used for each.

JSTL Tags

Functional Area

URI Prefix

Core actions http://java.sun.com/jsp/jstl/core c

XML processing actions

http://java.sun.com/jsp/jstl/xml x

Formatting actions

http://java.sun.com/jsp/jstl/fmt fmt

Relational database access

http://java.sun.com/jsp/jstl/sql sql

Function actions

http://java.sun.com/jsp/jstl/functions fn



The following table describes some of the core tag library tags.

JSTL Tags (Contd.)

Tag Purpose

c:out Evaluates an expression and outputs the result tothe current JspWriter

c:set Sets the value of a scoped variable or property

c:remove Removes a scoped variable

c:catch Catches a java.lang.Throwable that occurs in the body of the tag

c:if Evaluates the body of the tag if the expression specified by the test attribute is true



The following table describes some of the xml tag library tags.

JSTL Tags (Contd.)

Tag Purpose

x:parse Parses an XML document

x:out Evaluates the XPath expression and outputs the result to the current JspWriter

x:set Evaluates the XPath expression and stores the result in a scoped variable

x:choose Provides for a mutually exclusive conditional

x:otherwise Provides the final alternative within an x:choose element



The following table describes some of the format tag library tags.

JSTL Tags (Contd.)

Tag Purpose

fmt:setLocale Stores the specified locale in the localeconfiguration variable

fmt:bundle Creates an i18n localization context that is used in the tag body

fmt:setBundle Creates an i18n localization context and stores it in the scoped variable or the localization context configuration variable

fmt:message Finds the localized message in the resource bundle

fmt:param Supplies a parameter for replacement within a fmt:message element



The following table describes some of the database tag library tags.

JSTL Tags (Contd.)

Tag Purpose

sql:query Queries the database, storing the result set in a scoped variable

sql:update Executes an INSERT, DELETE, UPDATE, or SQL DDL statement, storing the result in a scoped variable

sql:transaction Establishes a transaction context for the sql:query and sql:update elements

sql:setDataSource Exports a data source either as a scoped variable or as the data source configuration variable

sql:param Sets the values for parameter markers (used with the sql:query and sql:update elements)



The following table describes some of the standard EL functions.

JSTL Tags (Contd.)

Tag Purpose

fn:contains Performs a case-sensitive test for a specifiedsubstring, returning true or false

fn:containsIgnoreCase Performs a case-insensitive test for aspecified substring, returning true orfalse

fn:endsWith Tests if a string ends with a specified suffix,returning true or false

fn:escapeXml Escapes characters that would beinterpreted as XML markup

fn:indexOf Returns the position of the first occurrenceof a specified substring



Investigate the use of core JSTL tags.

Demo 8-1: Developing JSP Pages Using Custom Tags



Solution:1. Investigate the c:out core tag.2. Investigate the c:remove core tag.

Demo 8-1: Developing JSP Pages Using Custom Tags (Contd.)



In this session, you learned that:Custom tags are fundamentally the same as standard tags, but you can acquire tag libraries from third parties and even build your own application-specific tags.JSTL provides a collection of general purpose tags.A tag library can be added to a JSP pages by using the <%@ taglib %> directive.Custom tags use standard XML tag syntax.Custom tags, standard tags, and EL eliminate all the scriptlet code in the JSP pages.

Summary



The next session covers Lab@Home. In this session, you need to perform exercises given in the following table.

Ensure to take the required input files from the faculty for performing these exercises.

What’s Next?

Chapter Number Exercise NumberChapter 5 (Book 2) Exercise 1Chapter 5 (Book 4) Exercise 1

Technology

Web component Development and JSP technologies session 13