CODEWITHSUNDEEP
tomcatlogging
Stephen Lam
Stephen Lam

Reputation: 65

Log any Tomcat-level exceptions that are handled by error-page in web.xml

I have the following lines in my web.xml that replace the stack trace rendering with a custom user-friendly error page.

<error-page>
  <location>/error.html</location>
</error-page>

What I am wondering is if it is possible to have Tomcat log any exceptions handled by the error-page element to a log file. If I used access logs, I would see 500s but I wouldn't be able to see the stack trace. How can I get the stack trace into a log?

Upvotes: 3

Views: 1221

Answers (1)

Will Keeling
Will Keeling

Reputation: 23054

You could create a dedicated servlet for handling errors.

<servlet>
        <servlet-name>ErrorHandler</servlet-name>
        <servlet-class>ErrorHandler</servlet-class>
</servlet>

<servlet-mapping>
        <servlet-name>ErrorHandler</servlet-name>
        <url-pattern>/ErrorHandler</url-pattern>
</servlet-mapping>

Then reference this in the <location> of the <error-page>:

<error-page>
  <location>/ErrorHandler</location>
</error-page>

And then implement the ErrorHandler servlet so that it logs the original exception before forwarding to the existing user friendly error page. For example:

public class ErrorHandler extends HttpServlet {

    private static final Log LOG = LogFactory.getLog(ErrorHandler.class);

    public void doGet(HttpServletRequest req, HttpServletResponse resp) {

        // Obtain the original exception
        final Throwable throwable = (Throwable) req.getAttribute("javax.servlet.error.exception");

        // Log the exception
        log.error("Caught unhandled exception: " + e, e);

        // Forward to the friendly error page
        RequestDispatcher rd = req.getRequestDispatcher("error.html");
        rd.forward(request, response);

        ...

    }
}

Upvotes: 3

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