JSP Error Handling

errorPage and isErrorPage Directives

JSP provides two page directives for error handling:

errorPage="url" — Specifies the JSP page to forward to when an unhandled exception occurs on the current page.
isErrorPage="true" — Marks a JSP as an error page, enabling access to the exception implicit object.

When an exception is thrown on a JSP with errorPage set, the container automatically forwards the request to the designated error page, passing the exception as an attribute.

errorPage and isErrorPage Directives

<%-- divide.jsp: page that may throw an exception --%>
<%@ page language="java" contentType="text/html; charset=UTF-8"
         errorPage="error.jsp" %>
<!DOCTYPE html>
<html>
<head><title>Division</title></head>
<body>
    <h2>Division Result</h2>
    <%
        int a = Integer.parseInt(request.getParameter("a"));
        int b = Integer.parseInt(request.getParameter("b"));
        // If b == 0, throws ArithmeticException
        // Container forwards to error.jsp automatically
        int result = a / b;
        out.println("Result: " + result);
    %>
</body>
</html>

<%-- error.jsp: designated error page --%>
<%@ page language="java" contentType="text/html; charset=UTF-8"
         isErrorPage="true" %>
<!DOCTYPE html>
<html>
<head><title>Error</title></head>
<body>
    <h2 style="color:red;">An Error Occurred</h2>
    <%-- 'exception' implicit object is available because isErrorPage="true" --%>
    <p><strong>Error Type:</strong> <%= exception.getClass().getName() %></p>
    <p><strong>Message:</strong> <%= exception.getMessage() %></p>
    <p><a href="javascript:history.back()">Go Back</a></p>
</body>
</html>

web.xml Error Mappings

The web.xml deployment descriptor allows you to define global error pages for the entire web application using <error-page> elements. You can map by HTTP error code or by exception type.

web.xml Error Code and Exception Mappings

<web-app>

    <!-- Map HTTP 404 to a custom JSP page -->
    <error-page>
        <error-code>404</error-code>
        <location>/WEB-INF/views/error-404.jsp</location>
    </error-page>

    <!-- Map HTTP 500 to a custom JSP page -->
    <error-page>
        <error-code>500</error-code>
        <location>/WEB-INF/views/error-500.jsp</location>
    </error-page>

    <!-- Map a specific exception type -->
    <error-page>
        <exception-type>java.lang.ArithmeticException</exception-type>
        <location>/WEB-INF/views/arithmetic-error.jsp</location>
    </error-page>

    <!-- Catch-all for any unhandled exception -->
    <error-page>
        <exception-type>java.lang.Throwable</exception-type>
        <location>/WEB-INF/views/generic-error.jsp</location>
    </error-page>

</web-app>

<%-- WEB-INF/views/error-404.jsp --%>
<%@ page language="java" contentType="text/html; charset=UTF-8" isErrorPage="true" %>
<!DOCTYPE html>
<html>
<head><title>404 - Page Not Found</title></head>
<body style="text-align:center; padding:60px;">
    <h1 style="font-size:80px; color:#e74c3c;">404</h1>
    <h2>Page Not Found</h2>
    <p>The page you are looking for does not exist.</p>
    <%-- Access error attributes set by the container --%>
    <%
        Integer statusCode = (Integer) request.getAttribute("javax.servlet.error.status_code");
        String requestUri  = (String)  request.getAttribute("javax.servlet.error.request_uri");
        if (requestUri != null) {
            out.println("<p>Requested URL: <code>" + requestUri + "</code></p>");
        }
    %>
    <a href="${pageContext.request.contextPath}/">Go to Home</a>
</body>
</html>

Exception Implicit Object and Error Attributes

When a JSP is designated as an error page (isErrorPage="true"), the exception implicit object is available. The servlet container also sets several request attributes you can use:

Attribute	Description
`javax.servlet.error.status_code`	HTTP status code (Integer)
`javax.servlet.error.exception_type`	Class of the exception (Class)
`javax.servlet.error.message`	Exception message (String)
`javax.servlet.error.exception`	The actual exception object (Throwable)
`javax.servlet.error.request_uri`	URI that caused the error (String)
`javax.servlet.error.servlet_name`	Name of the servlet that caused the error

Custom 500 Error Page with Full Details

<%-- WEB-INF/views/error-500.jsp --%>
<%@ page language="java" contentType="text/html; charset=UTF-8" isErrorPage="true" %>
<%@ taglib uri="http://java.sun.com/jsp/jstl/core" prefix="c" %>
<!DOCTYPE html>
<html>
<head><title>500 - Internal Server Error</title></head>
<body style="padding:40px;">
    <h1 style="color:#e74c3c;">500 - Internal Server Error</h1>
    <p>Something went wrong on our end. Please try again later.</p>

    <%-- Show details only in development mode --%>
    <%
        String env = application.getInitParameter("environment");
        if ("development".equals(env) && exception != null) {
    %>
        <div style="background:#f8d7da;padding:15px;border-radius:5px;margin-top:20px;">
            <h4>Debug Info (development only):</h4>
            <p><strong>Exception:</strong> <%= exception.getClass().getName() %></p>
            <p><strong>Message:</strong> <%= exception.getMessage() %></p>
            <p><strong>URI:</strong>
               <%= request.getAttribute("javax.servlet.error.request_uri") %></p>
            <pre style="overflow:auto;"><%
                java.io.StringWriter sw = new java.io.StringWriter();
                exception.printStackTrace(new java.io.PrintWriter(sw));
                out.println(sw.toString());
            %></pre>
        </div>
    <% } %>

    <p><a href="${pageContext.request.contextPath}/">Return to Home</a></p>
</body>
</html>

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JSP Error Handling

errorPage and isErrorPage Directives

web.xml Error Mappings

Exception Implicit Object and Error Attributes

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