Rework ErrorController now that getErrorPath() is unused and server.error.path must be used to configure the error path

[brucebrit]

Spring boot: 2.2.2
IDE: Spring Tool Suite

One of the ways to create a custom error page is to create a controller class that implements ErrorController. By overriding the getErrorPath() method and returning /error, I am able to return the expected my custom error page (located at resources/templates/customError.html).

But when I return another path, other than /error, I get the following error:

This localhost page can’t be found. No webpage was found for the web address: http://localhost:8080/bruce

Why is that so.

@Controller
public class MyErrorController implements ErrorController{

 // @RequestMapping("/error")
    @RequestMapping("/error1")
    public String handleError() {
        return "customError";
    }

	@Override
    public String getErrorPath() {

        //return "/error"; 
        return "/error1"; 
    }
}

Interestingly, I have done another experiment. The getErrorPath() returns /error1 , but I change the RequestMapping annotation to @RequestMapping("/error"), and that really return customError.html. This seems to imply that the path return by getErrorPath() is ignored.

[philwebb]

I have a feeling that the interface is unnecessary since Spring Boot 2.0, but I need to double check. I think that setting the server.error.path property is now the only way to customize the actual error path.

If I remember correctly, we used to use ErrorController to allow us to configure security, but we substantially simplified that in Spring Boot 2.0.

[brucebrit]

Hi, thanks for the response.
If that is the case, do we still need to implements ErrorController class, since server.error.path in the properties file is sufficient to achieve what we want.

[philwebb]

I don't think so, but I've not had time to confirm for sure yet.

[wilkinsona]

We don't call getErrorPath() anywhere, however implementing ErrorController is required at the moment to cause the auto-configuration of Boot's BasicErrorController to back off:

spring-boot/spring-boot-project/spring-boot-autoconfigure/src/main/java/org/springframework/boot/autoconfigure/web/servlet/error/ErrorMvcAutoConfiguration.java

Lines 106 to 112 in 2725264

	@Bean
	@ConditionalOnMissingBean(value = ErrorController.class, search = SearchStrategy.CURRENT)
	public BasicErrorController basicErrorController(ErrorAttributes errorAttributes,
	ObjectProvider<ErrorViewResolver> errorViewResolvers) {
	return new BasicErrorController(errorAttributes, this.serverProperties.getError(),
	errorViewResolvers.orderedStream().collect(Collectors.toList()));
	}

I'm not exactly sure what we should do here. An ErrorController marker interface with no methods feels like a bit of a smell, but it does provide a way of identifying the user's error controller and getting the auto-configured one to back off. I can't really think of a better alternative.

[wilkinsona]

For 2.3.x we could deprecate getErrorPath() and make it a default method so that it doesn't have to be implemented.

[scottfrederick]

ErrorController is currently a @FunctionalInterface. We can't add a default implementation for getErrorPath() without removing @FunctionalInterface, which could break backward compatibility if users are creating lambda expressions using ErrorController.