Catching Exceptions

If a particular type of problem frequently shows up in the log files, you may want to fine-tune the error handling and deal more gracefully with the problem. There’s a JSTL action named <c:catch>, described in Table 9-3, that can help you with this.

Table 9-3. Attributes for JSTL <c:catch>

Attribute name

Java type

Dynamic value accepted

Description

var
 
String

No

Optional. The name of the variable to hold the java.lang.Throwable if thrown by elements in the body.

Example 9-13 shows the top part of a modified version of the calc.jsp page that uses <c:catch> to catch divide-by-zero exceptions.

Example 9-13. Catching an exception (calc2.jsp)
<%@ page contentType="text/html" %>
<%@ taglib prefix="c" uri="http://java.sun.com/jsp/jstl/core" %>
<%@ page errorPage="errorpage.jsp?debug=log" %>
  
<html>
  <head>
    <title>Calculator</title>
  </head>
  <body bgcolor="white">
  
    <jsp:useBean id="calc" class="com.ora.jsp.beans.calc.CalcBean">
      <jsp:setProperty name="calc" property="*" />
    </jsp:useBean>
  
    <%-- Calculate the new numbers and state info --%>
    <c:catch var="error">
      <c:set var="currentNumber" value="${calc.currentNumber}" />
    </c:catch>
    <c:if test="${error != null}">
      <c:set var="currentNumber" value="Error" />
      <jsp:setProperty name="calc" property="reset" value="true" />
    </c:if>
    ...

The calc bean’s currentNumber property accessor method is the one that performs the calculation. By placing the <c:set> action with the EL expression that reads this property within the body of ...

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