Spring Boot Actuator provides an /error mapping by default that handles all errors in a sensible way, and it is registered as a “global” error page in the servlet container. For machine clients it will produce a JSON response with details of the error, the HTTP status and the exception message. For browser clients there is a “whitelabel” error view that renders the same data in HTML format (to customize it just add a View that resolves to “error”).

If you want more specific error pages for some conditions, the embedded servlet containers support a uniform Java DSL for customizing the error handling. For example:

@Bean
public EmbeddedServletContainerCustomizer containerCustomizer(){
    return new MyCustomizer();
}

// ...

private static class MyCustomizer implements EmbeddedServletContainerCustomizer {

    @Override
    public void customize(ConfigurableEmbeddedServletContainer factory) {
        factory.addErrorPages(new ErrorPage(HttpStatus.BAD_REQUEST, "/400"));
    }

}

You can also use regular Spring MVC features like @ExceptionHandler methods and @ControllerAdvice.