<error-page> tag in web.xml doesn't catch java.lang.Throwable Exceptions

Question

I have a web-app developed with servlet & JSP. I configured my app to throw an IllegalArgumentException if I insert bad parameters. Then I configured my web.xml file in this way:

<error-page>
    <error-code>404</error-code>
    <location>/error.jsp</location>
</error-page>
<error-page>
    <exception-type>java.lang.Throwable</exception-type>
    <location>/error.jsp</location>
</error-page>

When I rise a 404 error, then it works and calls error.jsp, but when I rise a java.lang.IllegalArgumentException, then it does not work and I've a blank page instead of error.jsp. Why?

The server is Glassfish, and logs show really IllegalArgumentException rised.

Answer 1

You should not catch and suppress it, but just let it go.

I.e. do not do:

@Override
protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
    try {
        doSomethingWhichMayThrowException();
    } catch (IllegalArgumentException e) {
        e.printStackTrace(); // Or something else which totally suppresses the exception.
    }
}

But rather just let it go:

@Override
protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
    doSomethingWhichMayThrowException();
}

Or, if you actually intented to catch it for logging or so (I'd rather use a filter for that, but ala), then rethrow it:

@Override
protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
    try {
        doSomethingWhichMayThrowException();
    } catch (IllegalArgumentException e) {
        e.printStackTrace();
        throw e;
    }
}

Or, if it's not an runtime exception, then rethrow it wrapped in ServletException, it will be automatically unwrapped by the container:

@Override
protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
    try {
        doSomethingWhichMayThrowException();
    } catch (NotARuntimeException e) {
        throw new ServletException(e);
    }
}

See also:

• How does server prioritize which type of web.xml error page to use?
• https://stackoverflow.com/questions/9739472/what-to-do-with-exceptions-why-and-when-does-doget-method-throw-servletexcept/9746657#9746657

Answer 2

I have today the same issue. (JavaEE 7 and Glassfish 4.0)

The problem seems that the framework check it as String instead with the Class.

String based check (the hypothesis)

When a Exception is twrown, e.getClass() is compared with <exception-type> as string. So you can't use inheritance.

Note that nested classes must be pointed as '$' instead '.' (same as getClass() method).

Class based check

The framework create an instance of the class, and <exception-type> text refer to it, and the class.isInstance() is used to check.

This will need reflection and policy file could break it.

I hope that this response solves future issues.