How to customize error page selection logic in Spring Boot

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Spring Boot provides a comprehensive error handling for web applications and REST services using its BasicErrorController. This class has an important extension point — ErrorViewResolver that allows us to customize the logic of selecting pages for different errors.

In a simple case, if you want to change how the “Whitelabel Error Page” looks like, you can simply create a custom page and put it into a conventional location. E.g. to handle error 404, just put a page named 404.html into resources/public/error folder of your project.

But this may not be enough if your pages are located in a different place or if you want to customize the logic used to select them for a particular error.

Suppose we have the following controller with a /goodpage and a /badpage that for some reason produces an error. We can use the bad page to simulate the server-side error:

@Controller
public class MyController {

    @GetMapping("/goodpage")
    public String goodpage() {
        return "good";
    }

    @GetMapping("/badpage")
    public String badpage() {
        throw new RuntimeException("Bad!");
    }

}

Now we want to show a special view located at resources/public/mycustomfolder/oops.html every time a nasty server-side 5xx error happens and keep the default…