index.jsp
<%@ taglib prefix="c" uri="http://java.sun.com/jstl/core" %>
<%@ taglib prefix="fmt" uri="http://java.sun.com/jstl/fmt" %>
<h1>Peter's Junk-Mail Service</h1>
<c:if test="${param.submitted}">
<c:if test="${empty param.name}" var="noName" />
<c:if test="${empty param.email}" var="noEmail" />
<c:if test="${empty param.age}" var="noAge" />
<c:catch var="ageError">
<fmt:parseNumber var="parsedAge" value="${param.age}" />
<c:if test="${parsedAge < 13}" var="youngAge" />
</c:catch>
<c:if test="${not empty ageError}" var="badAge" />
<c:if
test="${not (noName or noEmail or noAge or badAge or youngAge)}">
<c:set value="${param.name}" var="name" scope="request"/>
<c:set value="${param.email}" var="email" scope="request"/>
<c:set value="${param.age}" var="age" scope="request"/>
<jsp:forward page="spamFormHandler.jsp" />
</c:if>
</c:if>
<form method="post">
<input type="hidden" name="submitted" value="true" />
<P>
Enter your name:
<input type="text" name="name"
value="<c:out value="${param.name}"/>" />
<br />
<c:if test="${noName}">
<small><font color="red">
Note: you must enter a name
</font></small>
</c:if>
</p>
<P>
Enter your email address:
<input type="text" name="email"
value="<c:out value="${param.email}"/>" />
<br />
<c:if test="${noEmail}">
<small><font color="red">
Note: you must enter an email address
</font></small>
</c:if>
</p>
<P>
Enter your age:
<input type="text" name="age" size="3"
value="<c:out value="${param.age}"/>" />
<br />
<c:choose>
<c:when test="${noAge}">
<small><font color="red">
Note: you must enter your age
</font></small>
</c:when>
<c:when test="${badAge}">
<small><font color="red">
Note: I couldn't decipher the age you typed in
</font></small>
</c:when>
<c:when test="${youngAge}">
<small><font color="red">
Note: You're too young to receive pornographic
junk mail. Please grow older and try again.
</font></small>
</c:when>
</c:choose>
</p>
<input type="submit" value="Sign up" />
</form>
spamFormHandler.jsp
<%@ taglib prefix="c" uri="http://java.sun.com/jstl/core" %>
<h4>
<font face="arial">
Excellent! The information is now correct. (We could save it in a
database or process it further.)
</font>
</h4>
Download: JSTLSetParamValue.zip( 939 k)