Java Web Programming [5/9] : EL, JSTL and Custom Tags

Module 5: EL, JSTL and
Custom Tags

Thanisa Kruawaisayawan
Thanachart Numnonda
www.imcinstitute.com

Objectives

 Expression Language
 JSTL (JSP Standard Tag Library) 1.1
 Custom Tags

2

Expression Language
 EL expressions are ALWAYS within curly braces,
and prefixed with the dollar sign
${firstThing.secondThing}

 firstThing can be
 EL Implicit Object
 Attribute

3

EL Implicit Object and Attribute

EL Implicit Object  Attribute
 param  in page scope
 paramValues
 in request scope
 header  in session scope
 headerValues
 in application scope
 cookie

 initParam

 pageContext

 pageScope
 requestScope
 sessionScope
 applicationScope

4

EL Implicit Objects
Implicit Object Description
param Maps of all the form parameters that were
paramValues passed to your JSP
header Maps of all the request headers
headerValues
cookie A Map of all the cookies passed to your JSP
initParam A Map of the context init parameters
pageScope A Map of all the objects that have page,
requestScope request, session and application scope
sessionScope
applicationScope

5

hello.html
<form action="helloName.jsp" method="post">
Name: <input name="username">
<input type="submit">
</form>

6

param
<%-- helloName.jsp --%>
Hello <%= request.getParameter("username") %><br>
Hello <% out.print(request.getParameter("username"));%><br>
Hello ${param.username}<br>
Hello ${param['username']}<br>
Hello ${param["username"]}<br>

7

header
Host is ${header.host} <br>
Cookie is ${header.cookie}

8

cookie

JSESSIONID = ${cookie.JSESSIONID.value}

9

initParam
//web.xml
<web-app ...>
:
<context-param>
<param-name> driver </param-name>
<param-value> com.mysql.jdbc.Driver </param-value>
</context-param>
:
</web-app>
---------------------------------------------------------------------------
//InitParamEL.jsp
Driver is ${initParam.driver}

10

Person.java

package myBeans;

public class Person {
private String name;
public void setName(String name) {
this.name = name;
}
public String getName() {
return name;
}
}

11

EL and JavaBeans
<jsp:useBean id="personName" class="myBeans.Person" />
<jsp:setProperty name="personName" property="name" value="Thanisa" />

<%-- <jsp:getProperty name="personName" property="name" /> --%>

${personName.name}

12

Disable the EL
 For a single page
<%@ page isELIgnored="true" %>

 For an entire application
<jsp-property-group>
<url-pattern>*.jsp</url-pattern>
<el-enabled>false</el-enabled>
<scripting-invalid>true</scripting-invalid>
</jsp-property-group>

13

The taglib Directive

 Tag libraries come in two different flavors:
 JSTL (JavaServerPages Standard Tag Library)
 Custom Tag Libraries

 The syntax for the taglib directive is as follows:
<%@ taglib uri=“taglibraryURI” prefix=“tagPrefix” %>

14

JSTL 1.1
 The “Core” library  The “SQL” library
 Looping and Iteration  Database access
 <c:forEach>  <sql:query>
 <c:forTokens>  <sql:update>
 <sql:setDataSource>
 Conditional  <sql:param>
 <c:if>  <sql:dateParam>
 <c:choose>
 <c:when>
 <c:otherwise>
 The “Formatting” library
 <fmt:message>
 General-purpose :
 <c:out>
 <c:remove>
 <c:catch>  The “XML” library
 URL related  <x:parse>
 <c:import> :
 <c:url>
 <c:redirect>
 <c:param>

15

Download and copy JSTL Libraries to
Tomcat

16

Check JSTL in Project

17

Core Tag Library
 Looping and Iteration
 Conditional
 General-purpose
 URL related

18

Looping and Iteration
 <c:forEach>
 <c:forTokens>

19

<c:forEach>
<%@taglib uri="http://java.sun.com/jsp/jstl/core" prefix="c" %>

<table border="1" align="center">
<tr bgcolor="orange">
<th>Header Names and Values</th>
</tr>
<c:forEach var="h" items="${header}">
<tr>
<td>${h.value}</td>
</tr>
</c:forEach>
</table>

20

Conditionals

 <c:if>
 <c:choose>, <c:when> and <c:otherwise>

22

poll.html
:
<body>
<h3>Do you agree with the opposition
to boycott the election?</h3>
<form action = "vote.jsp" method = "post">
<input type=radio name=answer value="Yes"> Yes<br>
<input type=radio name=answer value="No"> No<br>
<input type=radio name=answer value="No Comment"> No Comment<br>
<br><input type=submit value="VOTE">
</form>
</body>
:

24

<c:if>
<%@taglib uri="http://java.sun.com/jsp/jstl/core"
prefix="c" %>

<c:if test="${param.answer == 'Yes'}" >
You vote for Yes
</c:if>
<c:if test="${param.answer == 'No'}" >
You vote for No
</c:if>
<c:if test="${param.answer == 'No Comment'}" >
You vote for No Comment
</c:if>

25

<c:choose>, <c:when> and
<c:otherwise>
<%@taglib uri="http://java.sun.com/jsp/jstl/core"
prefix="c" %>

<c:choose>
<c:when test="${param.field == 'Network'}" >
You choose Network
</c:when>
<c:when test="${param.field == 'Database'}" >
You choose Database
</c:when>
<c:otherwise>
You choose Programming
</c:otherwise>
</c:choose>

26

Scoped Variable Manipulation
 <c:out>
 <c:set>
 <c:remove>
 <c:catch>

27

<c:out>
<%@taglib uri="http://java.sun.com/jsp/jstl/core" prefix="c"%>

<c:forEach begin="3" end="15" step="3" var="index" varStatus="num">
<c:out value="${index}" />: <c:out value="${num.count}" /><br>
</c:forEach>

28

<c:set> and <c:remove>

<c:set var="status" scope="request" value="On-line" />
Status is ${status} <br>

<c:remove var="status" scope="request" />
Now, status is ${status}

29

<c:catch>

About to do a risky thing <br>
<c:catch var="myException" >
<% int x = 10/0; %>
</c:catch>
<c:if test="${myException != null}">
There was an exception: ${myException.message} <br>
</c:if>
If you see this, we survived.

30

URL Manipulation
 <c:import>
 <c:redirect>
 <c:url>
 <c:param>

31

<c:import>
<%-- Header2.jsp --%>
Information Technology KMITL
-----------------------------------------------------------------
<%-- Test2.jsp --%>
<c:import url="http://localhost:8084/SWP_Topic5/Header2.jsp" />
-----------------------------------------------------------------

 The <c:import> action can also
be used to specify absolute,
relative and FTP URL resources
to provide a lot more functionality
than the standard <jsp:include> action.
 <c:import> can reach OUTSIDE the
web app

32

<c:redirect>
Information Technology KMITL
-----------------------------------------------------------------
<%-- Test3.jsp --%>
<c:redirect url="http://localhost:8084/SWP_Topic5/Header3.jsp" />
-----------------------------------------------------------------

 The <c:redirect> action simply
sends an HTTP redirect to
a client.

33

<c:url> and <c:param>
${param.faculty}
-----------------------------------------------------------------
<%-- Test4.jsp --%>
<c:url value="http://localhost:8084/SWP_Topic5/Header4.jsp " >
<c:param name="faculty" value="Information Technology" />
</c:url>
-----------------------------------------------------------------
 The <c:url> action takes care of the encoding and all the URL rewriting.
http://localhost:8084/JSP2/Header.jsp;jsessionid=543ferew432esd23

34

SQL Tag Library
 <sql:setDataSource>
 <sql:query>
 <sql:update>
 <sql:param> and <sql:dateParam>
 <sql:transaction>

35

BookStore.jsp
<%@taglib uri="http://java.sun.com/jsp/jstl/sql" prefix="sql" %>

<html>
<head><title>ABC Book Store </title></head>
<body>
<center>
<form action="BookStore.jsp">
<h1> ABC Book Store </h1>
<br> Please select a Book and add it to your shopping cart
</p>

<sql:setDataSource var="datasource"
driver="com.mysql.jdbc.Driver"
url="jdbc:mysql:///test" user="root"
password="root" />

<sql:query var="books" dataSource="${datasource}" >
select * from books
</sql:query>

36

BookStore.jsp (cont.)
<table border="1" align="center">
<tr bgcolor="orange">
<td>ISBN</td><td>Title</td>
<td>Author</td><td>Price</td></tr>
<c:forEach var="row" items="${books.rows}">
<tr>
<td>${row.isbn}</td>
<td>${row.title} /></td>
<td>${row.author} /></td>
<td>${row.price} /></td>
<td><input type=submit value="add"></td>
</tr>
</c:forEach>
</table>
</form>
</center>
</body>
</html>

37

Custom Tag Libraries
 The JSP 1.1 specifications introduced the
ability to define new tags called custom tags
 Can be used in any number of JSP files
 A user can define how the tag, its attributes
and its body are to be interpreted, and then
group these tags into collections, called tag
libraries.

39

Simple Tag Files
1. Take an included file (such as “Header.jsp”) and rename it
with a .tag extension
<%-- Header.jsp --%>
<img src="Duke_Cont.png"><br><br>
Welcome to Java World!!
1. Put the tag file (such as “Header.tag”) in a directory named
“tags” inside the “WEB-INF” directory

1. Put a taglib directive (with a tagdir atttribute) in the JSP
(TestTag.jsp)
<%@taglib tagdir="/WEB-INF/tags" prefix="myTags" %>
<myTags:Header/>
40

Components that make up a Tag library
1. The Tag Library Descriptor (TLD) file
2. The Tag Handler class
 Classic
 Simple
1. The JSP file

42

Repeat Tag Implemented as a
Classic JSP 1.2 Tag Extension
<%@ taglib prefix="my"
uri="/mytags" %>
<my:repeat num="3">
Usage

tag body
</my:repeat>

int doStartTag() {
this.count = this.num;
Implementation

return Tag.EVAL_BODY_INCLUDE;
}

int doAfterBody() {
this.count--;
return (this.count > 0) ?
Tag.EVAL_BODY_AGAIN :
Tag.SKIP_BODY; 43
}

Repeat Tag Implemented as a
Simple JSP 2.0 Tag Extension
<%@ taglib prefix="my"
uri="/mytags" %>
Usage

<my:repeat num="3">
tag body
</my:repeat>

void doTag() {
Implementation

for( int i = 0; i < num; i++ ) {
getJspBody().invoke( null );
}
}

44

Create a TLD for the tag

45

Making a Simple Tag Handler

46

JSP File
 Import the tag library
 Specify location of TLD file and define a tag
prefix (namespace)
<%@ taglib uri="myTaglib" prefix="myPrefix" %>
 Use the tags
 <prefix:tagName />
 Prefix comes from taglib directive
 Tag name comes from tag added into TLD file
 Example <myPrefix:myTag />
47

Write a JSP that uses the tag
<%-- UseCustomTag.jsp --%>
<%@taglib uri="TestMyTag1" prefix="my" %>
<my:test1/>

48

Thank you

thananum@gmail.com
www.facebook.com/imcinstitute
www.imcinstitute.com

49

Java Web Programming [5/9] : EL, JSTL and Custom Tags

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