How to serve a custom html page for 404 errors?

[Anjum Naseer]

Hi,

Background

I am using Dropwizard 1.0.0 and have a YAML file that contains this for the server settings:

server:
  type: simple
  rootPath: /rest
  applicationContextPath: /app
  adminContextPath: /app/admin

  connector:
    type: http
    port: 8084

With this I am able to successfully create and server my REST resources off URL's like this:

http://<host>:8084/app/rest/<my-resource-name>

and my assets (i.e. html, css, js, images, etc) are served off URL's like this:

http://<host>:8084/app/path/to/asset/<asset-name>

where "path" cannot be "rest" as that is where my REST resources are served off.

My Dropwizard Application class overrides the initialize method and registers some bundles like so:

    @Override
    public void initialize(final Bootstrap<AppConfiguration> bootstrap)
    {
        bootstrap.addBundle(new AssetsBundle("/assets/", "/", "index.html", "assets"));
        bootstrap.addBundle(new AssetsBundle("/node_modules/", "/node_modules/", null, "node_modules"));
        ...
    }

and also overrides the run method and registers my REST resources like so:

    @Override
    public void run(final AppConfiguration configuration, final Environment environment)
    {
        environment.jersey().register(new MyRestResource1());
        environment.jersey().register(new MyRestResource2());
        ...
    }

The application itself is built using Maven which produces a shaded JAR.

My assets (i.e. html, css, js, images, etc), however, are not included in this shaded JAR. I have kept them separate and have modified my POM file accordingly by using the maven-jar-plugin to add the folder containing all my assets to the JAR file. For reference this is the POM section that does that:

<plugin>
   <groupId>org.apache.maven.plugins</groupId>
   <artifactId>maven-jar-plugin</artifactId>
   <version>3.0.2</version>
   <configuration>
      <archive>
         <manifest>
            <addDefaultImplementationEntries>true</addDefaultImplementationEntries>
            <addClasspath>true</addClasspath>
         </manifest>
         <manifestEntries>
            <Class-Path>./path/to/where/my/assets/reside/</Class-Path>
         </manifestEntries>
      </archive>
   </configuration>
 </plugin>

Everything is working as expected.

Question

I now want to handle cases where the user either types a URL to an unknown REST request like:

http://<host>:8084/app/rest/some-unknown-REST-resource

or to an unknown asset like either of these:

http://<host>:8084/app/path/to/unknown-asset-folder/<asset-name>

http://<host>:8084/app/path/to/asset/<unknown-asset-name>

In the above cases I want to serve a custom 404 page.

What is the best way of achieving this?

What I've already tried

1. I have registered a custom RuntimeException ExceptionMapper in my applications run method.

This however only seems to kick-in on unknown REST resources. Trying to access unknown assets stills serves the default 404 page.

2. I tried creating a DefaultResource as described here: how-to-view-custom-404-page-in-dropwizard

but that did no seem to work.

3. I found this article: Jetty Custom Error Pages

and I really would like to use the first method described there that makes use of web.xml but am not sure how to use this with Dropwizard.

4. I tried looking in the Dropwizard configuration reference here: Reference

but could not find anything related to my requirements.

[Doug Patriarche]

Hi Anjum,

One way to serve custom pages for HTML errors is to use Jetty's error handler facility. In your Application.run() method add lines like these:

public class MyApplication extends Application<MyConfiguration> {
    // ...
    @Override
    public void run(final MyConfiguration configuration, final Environment environment) {
        // ...

        final ErrorPageErrorHandler epeh = new ErrorPageErrorHandler();
        // 400 - Bad Request, leave alone
        epeh.addErrorPage(401, "/error/general-error");
        epeh.addErrorPage(402, "/error/general-error");
        epeh.addErrorPage(403, "/error/403");
        epeh.addErrorPage(404, "/error/404");
        epeh.addErrorPage(405, 499, "/error/general-error");
        epeh.addErrorPage(500, 599, "/error/general-error");
        environment.getApplicationContext().setErrorHandler(epeh);

        // ...
    }
}

Then define the /error/* handlers like you do for any other Jersey resource.

Regards,

Douglas

[Anjum Naseer]

Douglas - You Sir, are a genius!

I have been rattling my brain for several days trying to solve this - thank you very much indeed for pointing me in the right direction :)

Cheers.