How to implement a custom 404 error page on App Engine, Java?

Question

Hi I'm trying to set up a static error page for 404 not found errors on app engine.

According to https://developers.google.com/appengine/docs/java/config/webxml#Error_Handlers: it says 404 cannot be customized.

And according to: https://developers.google.com/appengine/docs/java/config/appconfig#Custom_Error_Responses it don't seem to support 404 too.

However, https://groups.google.com/forum/?fromgroups=#!topic/google-appengine-java/3C-pY5ta2HQ, seems to suggest that 404 error page can be customised. I'm confused right now.

Answer 1

i realised this problem happens when running the app on local dev server. however, when i deploy the app to app engine. i can see the 404 error page that was configured using web.xml. thanks for all your help.

Answer 2

Why don't you use a Java EE <error-page> entry for these purposes?

in your web.xml:

<error-page>
    <error-code>404</error-code>
    <location>/app/error/404</location>
</error-page>
....
<error-page>
    <error-code>500</error-code>
    <location>/app/error/500</location>
</error-page>

You can combine it with Spring and get a general error-controller like:

....   
@Controller
public class ErrorController {

@RequestMapping(value = "/error/{errorCode}")
public final String errorCode(
        @PathVariable("errorCode") final String errorCode,
        final ModelMap modelMap) {
    modelMap.put("statusCode", errorCode);
    return "redirect:/ui/error.htm";
}

and your jsp-like file:

<h2>Error!!!</h2>
....
<h3>Status code: #{param.statusCode}</h3>

Hope this helps.

Answer 3

You are correct, this is not currently available in Java on App Engine. However, there is a workaround for Python. For an example on this, you can take a look at GAE Boilerplate.

Hope this helps.

Answer 4

I've been able to get the 404 errors successfully redirected in App Engine SDK versions 1.6.1 and earlier on my local dev server. However, after updating to GAE SDK 1.7.5 I cannot get it to work locally. I've since read that it's not currently supported for 404's as stated above.

Answer 5

From Google App Engine Standard environment documentation (Aug-19 2018):

In short, you must have a servlet mapping for this URL as follow:

<web-app>
    <servlet>
        <servlet-name>404</servlet-name>
        <jsp-file>/404.jsp</jsp-file>
    </servlet>
    <servlet-mapping>
        <servlet-name>404</servlet-name>
        <url-pattern>/404</url-pattern>
    </servlet-mapping>

    ...

    <error-page>
        <error-code>404</error-code>
        <location>/404</location>
    </error-page>
</web-app>

This configuration works as expected. The error page is shown while trying to get a page that does not exist (eg. www.domain.com/unknownPage).

Answer 6

At app engine version 1.9.48 this is working on the cloud:

[ web.xml ]

<web-app>

    ...    

    <error-page>
        <error-code>404</error-code>
        <location>/static-error.html</location>
    </error-page>
</web-app>

Answer 7

Its official.. it will not be supported: https://cloud.google.com/appengine/docs/flexible/java/configuring-the-web-xml-deployment-descriptor