Reasons for 404 error in Spring Boot

• Endpoint URL or HTTP Method Mismatch: We should check that the URL we’re trying to access matches the endpoint URL defined in the controller. Additionally, we need to verify the HTTP methods used for API URLs such as POST, GET, PUT, DELETE, and other methods.
• Controller Mapping Issue: We need to confirm that our controller class is annotated with @RestController or @Controller.
• Spring Boot Configuration Issue: We need to check if our application is running and if there are no other applications running on the same port number. Also, we should verify if we are using a custom server port.
• Path Variable or Request Parameter Mismatch: If we have defined a path variable in the controller, we should ensure it is referenced properly in the API URL.
• Typographical Errors: We need to check for typos in the endpoint mapping and the URL used to access the endpoint.
• Cross-Origin Resource Sharing Issue: If we are accessing the endpoint from a different domain, we should check if CORS is configured appropriately using @CrossOrigin.

Troubleshooting Ways:

• Check Endpoint Definitions
• Verify Application Status
• Examine Logs
• Test with API URLs with Postman tool you want to use other tools also.
• Check Spring Boot Configuration

The Spring Boot framework is one of the most famous in web application development, It can provide a lot of features to make development easy like dependency management, Spring Security, Spring Autoconfiguration, and other features provided by the Spring Framework. In this article, we will learn how a 404 error occurs while accessing the REST Controller on localhost. There are a lot of reasons for this error. We will get to know why this error is and what are the best solutions for this.

A 404 error when trying to access a RestController in Spring Boot can caused by various issues. The Rest Controller is created by using @RestController Annotation in Spring. Here are some reasons and troubleshooting steps to resolve the problem.