Check Parameter Value and Output Error Message : Form Input « JSTL « Java Tutorial

1. Java Tutorial
2. JSTL
3. Form Input

<%@ 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" />

  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>

  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>


  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">
       Please grow older and try again.
     </font></small>
    </c:when>
  </c:choose>
  </p>

  <input type="submit" value="Sign up" />

</form>

<%@ 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>

24.15.Form Input
	24.15.1.	Use ForEach to List All Form Parameters
	24.15.2.	Set Parameter Value
	24.15.3.	Get Date value from Form
	24.15.4.	Parse input from Form
	24.15.5.	JSTL Form Error Check and Forward
	24.15.6.	Use JSTL to Create URL From Form Input
	24.15.7.	Check Parameter Value and Output Error Message