“This Application Has No Explicit Mapping For /Error, So You Are Seeing This As A Fallback” is one of the developer’s most annoying error statements. This error occurs when you run your Java-based applications using Springboot.
Spring boot creates a server application that even accepts HTTP requests. It provides production-ready features like health checks, including third-party libraries and other configurations.
We don’t even need to write XML configurations; only some annotations can be used, which increases productivity and reduces the development phase.
It will create an HTML interface for you to test run your applications. But sometimes, you will find an error on your interface. This generic error is also hard to find because the system doesn’t identify it.
Table of Contents
What Causes The Error?
This error can occur due to many reasons, and we will be covering them all one by one below.
Main Application Class Is At Wrong Location
The official documentation manual for the Spring boot application suggests that we should place the main application class above all the other classes.
Problem With Idea Directory Structure
Spring boot uses a text editor or an IDE. All your java applications will be coded in a text editor. The text editor will be connected to your spring boot application so that it can make an interface for you to test run your application. Now, this error can occur when your IDEA directory structure is not right, and the application startup class is at the wrong location. The application startup class contains all the sub-packages, and also the controller package should be in the same class as the startup class, but when we place them in different classes, we will get the same error. Like in the example below:
As you can see, the Demo01 Application is the startup application class, and the controller class is a separate class.
Wrong Controller URL Path Configuration In Main Code
Whitelabel Error Page
How To Fix It
Using Springboot Annotation
@Springbootapplication -> this Annotation must be used at the start of your application then the rest of the classes should be added. This Annotation contains all the required information that the framework needs to process the application. Scanning components is a crucial part of the Spring boot application as it tells how many components the application has, what they do and how to manage them accordingly.
This is the pattern in writing code that will emit this error.
While working with Spring boot, you should remember that your .java file should always have
@springbootapplication annotation on the top.
Hopefully, this will prevent you from receiving the “This Application has no explicit mapping for /error, so you are seeing this as a fallback” error.
Adding Startup Class And Controlling Class In The Same Class
The error can be resolved by adding the controller class and the startup class in the same class.
After this refresh, the page and you should no longer face the “This Application has no explicit mapping for /error, ” so you see this as a fallback problem.
Correct Controller URL Path Configuration
In the startup application code before the public class, we can specify the location of the “Controller”. By doing this, we won’t get any errors, and the system will be able to identify by itself where the controller file is. Like in the following code, we added the line:
This can be used in the main startup application. Another way to do this is by setting the server error Whitelabel enabled to false by using the following command:
This can also be done in the main startup application. The startup application is where the spring boot starts scanning the code, which is an important part because it tells the framework how many packages and sub-packages are there.
It also tells where each of the packages resides and how to manage them in such a way that the application runs smoothly.
That’s why it is important to list the packages in the main startup application so that the framework knows what to do and what not to do.
To accurately define and configure scanning behaviours. These annotations can easily be used in a single shortcut annotation: @SpringBootApplication.
Now this solution raises a question if the error handler is disabled, then how will errors be handled.
The answer to your question is that we will only be disabling the container of Whitelabel error. There are different containers for different types of errors, so the rest of the execution will not be affected.
The rest of the errors will be identified but you still have to be cautious about the controller file being handled by the spring boot application.
To explore this solution, you have to understand what APIs are, what REST APIs are and when they can be considered RESTful APIs.
API stands for Application Programming Interface. It is a set of protocols and rules used to build and integrate an application software.
It’s like a medium between the user and the computer. It helps us communicate with the system and tell it what it should do so that the system can understand and fulfil your requirements.
REST stands for Representational State Transfer, an application programming interface with different architectural constraints, such as URI (uniform resource identifier), request metadata, caching, authorization, cookies, and so much more.
Spring boot consists of different REST APIs for different types of tasks, and different annotations can be used to access those APIs.
By using exceptional handling, we can configure or use such annotations that can emit error messages by making an exception for them. It’s like telling the system that this type of error can be ignored.
Following are some of the commonly used exceptional handlers:
@ContrllerAdvice Annotation:This is a global annotation that can be used to handle errors. It mostly acts as an interceptor of exceptions that the @RequestMapping annotation highlights.
ResponseEntityExceptionalHandler Class: This feature is used within the @ControllerAdvice classes, which allows the developer to specify some templates for ResponseEntity and return values. It’s like redirecting the system towards an answer to the error when the error occurs.
@RESTControllerAdvice Annotation: This feature was introduced in Spring 1.4, which led to easier exception handling as it consisted of both @ControllerAdvice and @Responsebody annotations.
ResponseStatusException Class: This is a new feature introduced in Spring 5. This class supports the application of HTTP status codes to HTTP responses; by delivering the appropriate status code to the client in the response, a RESTful application can let the user know if an HTTP request was successful or unsuccessful.
These are the three main reasons why the “This Application has no explicit mapping for /error, so you are seeing this as a fallback” problem occurs.
You check for these mistakes in your application while using Spring boot; after correcting these mistakes, just reload again, and your application will be able to run correctly.
Conventional methods are easy to use as we try to find the error and remove it, but in non-conventional methods, we try to make exceptional cases using different annotations, or we just disable the Whitelabel error page completely.
With the help of this article, I hope you will be able to resolve your error easily with the method that fits your situation.
Frequently Asked Questions
What is the use of the Spring boot framework?
Spring boot is essentially used to develop apps that can run on their own. Apps created on the spring boot framework do not need external servers to run but rather use embedded servers such s Netty.
Is there a difference between the Spring and Spring boot frameworks?
As the name indicates, yes, there are multiple differences. For example, the Spring framework requires multiple dependencies to create an app, whereas in comparison springbok framework only requires one. Spring boot also provides default configurations, whereas spring framework requires you to manually set up all configurations.
What is the Whitelabel Error page?
The white label error page is a generic error page which is shown when no custom error page is located.