The JSTL <c:catch> tag is used to catch exceptions that might be thrown during the processing of a JSP page. This tag is part of the JSTL core tag library, and is typically used in conjunction with the <c:if> tag to handle exceptions gracefully.

The basic syntax for the <c:catch> tag is as follows:

<c:catch var="exceptionVariable">
    <!-- JSP code that may throw an exception -->
</c:catch>

The attributes of the <c:catch> tag are as follows:

• var: The name of the variable to store the exception in. This attribute is required.

Here's an example that shows how to use the <c:catch> tag to catch an exception that might be thrown during the processing of a JSP page:

<c:catch var="myException">
    <%
        // This JSP code might throw an exception
        int x = 1 / 0;
    %>
</c:catch>

<c:if test="${not empty myException}">
    An error occurred: ${myException.message}
</c:if>

In this example, the <c:catch> tag is used to catch an exception that might be thrown when dividing the integer 1 by 0, which is an illegal operation. The caught exception is stored in the myException variable.

The <c:if> tag is then used to test whether the myException variable is not empty, which means that an exception was indeed caught. If the myException variable is not empty, an error message is displayed that contains the message of the caught exception.

Note that the <c:catch> tag should be used sparingly, as it can make debugging more difficult by hiding exceptions that might be useful for diagnosing problems. It is generally better to handle exceptions in a more structured way, such as by using try-catch blocks in Java code or by using error pages in JSP.